Review Article Cyanobacteria: Photoautotrophic …downloads.hindawi.com/journals/bmri/2015/754934.pdfReview Article Cyanobacteria: Photoautotrophic Microbial Factories for the Sustainable

Review ArticleCyanobacteria Photoautotrophic Microbial Factories forthe Sustainable Synthesis of Industrial Products

Nyok-Sean Lau1 Minami Matsui2 and Amirul Al-Ashraf Abdullah13

1Centre for Chemical Biology Universiti Sains Malaysia 11900 Bayan Lepas Penang Malaysia2Synthetic Genomics Research Team RIKEN Centre for Sustainable Resource Science Biomass Engineering Research DivisionYokohama Kanagawa 230-0045 Japan3School of Biological Sciences Universiti Sains Malaysia 11800 Penang Malaysia

Correspondence should be addressed to Amirul Al-Ashraf Abdullah amirulusmmy

Received 3 April 2015 Accepted 16 June 2015

Academic Editor Zongbao K Zhao

Copyright copy 2015 Nyok-Sean Lau et alThis is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Cyanobacteria are widely distributed Gram-negative bacteria with a long evolutionary history and the only prokaryotes thatperform plant-like oxygenic photosynthesis Cyanobacteria possess several advantages as hosts for biotechnological applicationsincluding simple growth requirements ease of genetic manipulation and attractive platforms for carbon neutral productionprocess The use of photosynthetic cyanobacteria to directly convert carbon dioxide to biofuels is an emerging area of interestEquipped with the ability to degrade environmental pollutants and remove heavy metals cyanobacteria are promising tools forbioremediation and wastewater treatment Cyanobacteria are characterized by the ability to produce a spectrum of bioactivecompoundswith antibacterial antifungal antiviral and antialgal properties that are of pharmaceutical and agricultural significanceSeveral strains of cyanobacteria are also sources of high-value chemicals for example pigments vitamins and enzymes Recentadvances in biotechnological approaches have facilitated researches directed towards maximizing the production of desiredproducts in cyanobacteria and realizing the potential of these bacteria for various industrial applications In this review the potentialof cyanobacteria as sources of energy bioactive compounds high-value chemicals and tools for aquatic bioremediation and recentprogress in engineering cyanobacteria for these bioindustrial applications are discussed

1 Introduction

Cyanobacteria also referred to as blue-green algae are theoldest photosynthetic organisms on earth that originatedapproximately 26ndash35 billion years ago [1] Indeed the originof photosynthetic organelle in eukaryotes is thought to havepossibly arisen by the process of endosymbiosis between aphagotrophic host and a cyanobacterium [2] Cyanobacteriaare morphologically diverse and exist in different formsincluding unicellular filamentous planktonic or benthic andcolonial (coccoid) ones [3 4] They are by far the mostwidespread occurring photosynthetic organisms They canthrive in a wide range of ecological habitats ranging frommarine freshwater to terrestrial environments Cyanobacte-ria are also well known for their ability to perform differentmodes of metabolism and the capacity to switch rapidlyfrom one mode to another [5] All cyanobacteria are capable

of oxygenic photosynthesis but some cyanobacterial speciescan switch to sulfide-dependent anoxygenic photosynthesis[6] In dark or under anoxic conditions cyanobacteria canperform fermentations for energy generation [7] Some fila-mentous cyanobacteria have evolved specialized cells knownas heterocysts to carry out nitrogen fixation [8]

At present many bioindustrial processes rely on thefermentations of heterotrophic bacteria to produce variousfine chemicals such as vitamins enzymes and amino acidsNevertheless the economic viability of these productionschemes is limited by the cost of carbon substrates used in thefermentation processes Cyanobacteria endowed with pho-tosynthesis system to fix carbon dioxide into reduced formare ideal biosynthetic machinery for sustainable productionof various chemicals and biofuels Unlike heterotrophicbacteria cyanobacteria require only sunlight carbon dioxidewater andminimal nutrients for growth eliminating the cost

Hindawi Publishing CorporationBioMed Research InternationalVolume 2015 Article ID 754934 9 pageshttpdxdoiorg1011552015754934

2 BioMed Research International

of carbon sources and complex growth media Sunlight is themost readily available and inexpensive resource on earth andthe use of cyanobacteria for the production of fine chemicalsand biofuels from solar energy offers a greener path for thesynthesis process Equipped with superior photosynthesiscapabilities cyanobacteria have higher photosynthesis andbiomass production rates compared to plants and can convertup to 3ndash9 of the solar energy into biomass compared tole025ndash3 achieved by crops for example corn sugar cane[9] They also require less land area for cultivation thanterrestrial plant reducing the competition for arable landwith crops intended for human consumption Cyanobacteriautilize carbon dioxide a type of greenhouse gases duringphotosynthesis and help to achieve a carbon neutral pro-duction process Being prokaryotes cyanobacteria possessrelatively simple genetic background that eases manipulation[10] In addition the residual cyanobacteria biomasses thatare left over after high-value products extraction can be usedas animal feed or converted into organic fertilizer

Considering the aforementioned inherent merits ofcyanobacteria they are one of the attractive candidates foruse in diverse biotechnological application With the recentadvances in genetic and metabolic engineering technologiesand the availability of more than 300 cyanobacterial genomesequences there is significant progress in research directedtowards realizing the full potential of these photosyntheticbacteria Cyanobacteria have gained considerable attention inrecent years for their possible use in agriculture nutraceu-ticals effluent treatment and the production of biofuelsvarious secondary metabolites including vitamins toxinsand enzymes In this paper the recent progress in developingcyanobacteria for various potential applications in biotech-nology is discussed

2 Potential Applications of Cyanobacteria asEnergy Sources

Anticipation of depletion of fossil fuel resources and globalwarming have spurred vigorous research initiatives aimedat developing carbon neutral alternatives to supplement orreplace fossil fuels Several alternatives to current fossil fuelshave been proposed and they include ethanol 1-butanolisobutanol hydrogen gas and alkanes

The production of ethanol via biological route hasreceived widespread attention in recent years Traditionallya two-step route to first collect plant-derived biomass andsubsequent conversion of the biomass to fuels by microbialfermentation is employed [30] This indirect productionscheme is inefficient in the conversion of biomass to fuels[31] and thus there are increasing interests in the use ofphotosynthetic microbes to directly convert carbon dioxideto fuels Although some cyanobacterial strains naturallyproduce low level of ethanol as a byproduct of naturalfermentation it is necessary to enhance the production effi-ciency of cyanobacteria to reach an economically viable levelAn attempt to introduce the pyruvate decarboxylase (pdc)and alcohol dehydrogenase II (adh) genes from Zymomonasmobilis into the chromosome of Synechocystis sp PCC 6803was reported [11] (Figure 1) Photosynthetic production of

up to 550mgL ethanol was achieved in the engineeredSynechocystis sp [32] Further engineering of Synechocystissp by overexpressing endogenous alcohol dehydrogenaseand disrupting polyhydroxyalkanoate biosynthetic pathwayincreased ethanol production up to 5500mgL [12] (Table 1)Isobutanol and 1-butanol are considered as better substitutesfor gasoline compared to ethanol as they have greater energydensity being less corrosive and less volatile [33] Using asimilar genetic modification approach direct photosyntheticproduction of isobutanol in cyanobacteria is also feasibleTheintroduction of an artificial isobutanol biosynthesis pathwayinto Synechococcus elongatus PCC 7942 had resulted in theproduction of isobutyraldehyde and isobutanol up to 1100 and450mgL respectively [13]

More than 14 genera of cyanobacteria are known toproduce hydrogen under various culture conditions and theyinclude Anabaena Aphanocapsa CalothrixMicrocystisNos-toc andOscillatoria [15 34ndash36] In heterocystous or filamen-tous cyanobacteria hydrogen gas is produced as a byproductof nitrogen fixation under nitrogen limiting growth con-ditions In cyanobacteria the production of hydrogen gasis also facilitated by the reversible activity of hydrogenasesenzymes Two distinct types of hydrogenases are present indifferent cyanobacterial species uptake hydrogenases thatoxidize oxygen bidirectional or reversible hydrogenases thatcan both take up or produce hydrogen [37] The efficiencyof hydrogen production in some cyanobacteria is limitedby the extreme oxygen sensitivity of hydrogenases and thetendency for [NiFe] hydrogenases to thermodynamicallyfavor hydrogen uptake [38] Increased production of hydro-gen is achievable by blocking pathways that compete forreductant consumption with hydrogenases The disruptionof ldhA gene that is responsible for NADH consumptionin lactate production in Synechococcus sp PCC 7002 hadresulted in a significant increase in the NADHNAD+ ratioand a concomitant fivefold increase in hydrogen produc-tion by the native bidirectional [NiFe] hydrogenase [39]In another example enhanced hydrogen production in Selongatus PCC 7942 was obtained through heterologousexpression of exogenous [FeFe] hydrogenases (HydA) fromClostridium acetobutylicum [16] The expression of [FeFe]hydrogenases that thermodynamically favor hydrogen pro-duction relative to [NiFe] hydrogenase can modulate redoxflux in the heterologous host resulting in higher hydrogenproduction Metabolic engineering of cyanobacteria by redi-recting glycogen catabolism through the oxidative pentosepathway was found to enhance intracellular NADPH con-centrations and consequently improve the hydrogen yieldIn the glyceraldehyde-3-phosphate (gap1) gene deletion andNAD+-glyceraldehyde-3-phosphate (GAPDH-1) overexpres-sion strains of Synechococcus sp PCC 7002 23-fold and3-fold increase in hydrogen production respectively wereobtained compared to the wild type [40]

Some cyanobacteria are known to synthesize alkanesor alkenes that have desirable properties for combustionStudies on the alkane biosynthetic pathways in cyanobacteriarevealed that the two important enzymes acyl-acyl carrierprotein reductase and aldehyde decarbonylase are responsi-ble for the conversion of fatty acid metabolism intermediates

BioMed Research International 3

3-PGA

G3P

F6P

RuBP Calvin cycle

PEP

Pyruvate

DXP

HMBPP DMAPP

Acetaldehyde

2-Ketoisovalerate Isobutyraldehyde

Acetyl-CoA

Fatty acids Fatty aldehyde

Isoprene

Ethanol

Isobutanol

PHB

Alkanesaar adc

adh

kivd

ispS

alsS ilvC ilvD

NADPH

FNR

FdHydrogen gashydA

PSII PSI

Light Light

adh

pdc

eminus

H+H2O

Ctb6f

CO2

2H++ 12O2

Figure 1 A schematic representation of biochemical pathways for various industrial products synthesis in cyanobacteria 3-PGA 3-phosphoglycerate aar aldehyde decarbonylase adc alcohol dehydrogenase alsS acetolactate synthase F6P fructose-6-phosphate FNRferredoxin NADP+ reductase G6P glucose-6-phosphate HydA [FeFe] hydrogenase ilvD dihydroxy-acid dehydratase ilvC acetohydroxyacid isomeroreductase pdc pyruvate decarboxylase PEP phosphoenolpyruvate PHB polyhydroxybutyrate

Table 1 Biofuels production in cyanobacteria

Cyanobacteria Compound Production ReferencesSynechococcus elongatus PCC 7942 Ethanol 230mgL [11]Synechocystis sp PCC 6803 Ethanol 5500mgL [12]Synechococcus elongatus PCC 7942 Isobutanol 450mgL [13]Synechococcus elongatus PCC 7942 Isobutyraldehyde 1100mgL [13]Synechococcus elongatus PCC 7942 1-Butanol 299mgL [14]Anabaena sp PCC 7120 Hydrogen 26 120583molmgminus1 chl a hminus1 [15]Anabaena cylindrica IAMM-1 Hydrogen 21 120583molmgminus1 chl a hminus1 [15]Nostoc commune IAMM-13 Hydrogen 025 120583molmgminus1 chl a hminus1 [15]Synechococcus elongatus PCC 7942 Hydrogen 28 120583molmgminus1 chl a hminus1 [16]Synechococcus sp PCC 7002 n-Alkanes 5 dry cell weight [17]Synechocystis sp PCC 6903 Fatty acids 197mgL [18]

to alkanes or alkenes [41 42] Heterologous expression ofgenes encoding these two enzymes had conferred the abilityto produce and secrete alkane in Escherichia coli [43] Inaddition the expression of acyl-acyl carrier protein reductaseand aldehyde decarboxylase genes from S elongatus PCC7942 in Synechococcus sp PCC 7002 was found to increasealkane production in the heterologous host [17] In anotherexample the overexpression of both acyl-acyl carrier pro-tein reductase and aldehyde-deformylating oxygenase fromseveral cyanobacterial strains was shown to increase alka-nesalkenes yield by twofold [44] The production of various

biofuel precursors including alkanes fatty acids and waxesters from fatty aldehydes was achievable in Synechocystissp PCC 6803 through pathway engineering Overexpressionof acyl-ACP reductase the enzyme that converts the endproduct of fatty acid biosynthesis into acyl aldehyde resultedin a significant improvement in fatty acids production inSynechocystis sp in addition to alkane production [45] Inanother study the coproduction of alkanes and 120572-olefins wasobserved in Synechococcus sp NKBG15041c by expressing theacyl-acyl carrier protein reductasealdehyde-deformylatingoxygenase pathway genes from S elongatus PCC 7942 [46]


Table 2 Potential uses of cyanobacteria in bioremediation of wastewater

Cyanobacteria Types of wastewater Compounds removed ReferencesPhormidium bohneri Industrial effluent (cheese factory) NO

3

minus and PO4

3minus [19]Phormidium bohneri Swine manure effluent NH

4

+ and PO4

3minus [20]Oscillatoria sp Activated sludge effluent NO

3

minus and PO4

3minus [21]Schizothrix calcicola Phormidium subfuscumPhormidium tenue and Oscillatoria sp Synthetic wastewater NO

3

minus and PO4

3minus

Spirulina indica Spirulina maxima and Spirulinaplatensis Synthetic heavy metal solution Nickel and zinc [22]

Anabaena doliolum Chlorella vulgaris Synthetic wastewater Copper iron NH4

+ andNO3

minus[23]

Nostoc sp PCC 7936 Industrial wastewater [chromium(VI) plating industry] Chromium (VI) [24]

Anabaena oryzae Anabaena variabilis andTolypothrix ceytonica

Mixed domestic-industrialwastewater

Organic matter copper andzinc [25]

Synechocystis sp PUPCCC 64 Synthetic insecticide solution Chlorpyrifos [26]Westiellopsis prolifica Nostoc hatei andAnabaena sphaerica Synthetic insecticide solution Carbofuran chlorpyrifos and

endosulfan [27]

Synechocystis sp PUPCCC 64 Synthetic herbicide solution Anilofos [28]Anabaena oryzae Nostoc muscorum andSpirulina platensis Synthetic pesticide solution Malathion [29]

3 Role of Cyanobacteria inAquatic Bioremediation

In recent years biological waste treatment systems in par-ticular the use of cyanobacteria in wastewater treatmenthave attracted considerable scientific and technical interestCyanobacteria are characterized by the ability to oxidize oilcomponents complex organic compounds and accumulatemetal ions for example Zn Co andCu [47]Thus cyanobac-teria are promising tool for the secondary treatment of urbanagricultural or industrial effluents (Table 2)

The potentials of cyanobacteria in the removal of nutri-ents from wastewater rich in nitrogenous and phospho-rus compounds have been demonstrated The ability toremove nitrogenous and phosphate ions fromwastewater wasobserved in cyanobacteria such as Oscillatoria PhormidiumAphanocapsa and Westiellopsis [19ndash21 48] The biomassof Spirulina strains contains different functional groupsfor example carboxyl hydroxyl sulfate and other chargedgroups that are important for metal binding They have greatpotentials in metal pollution control and the biosorptionof zinc and nickel by several strains of Spirulina namelySpirulina indica Spirulina maxima and Spirulina platensiswas investigated recently [22] Pesticide application is knownto have negative impacts on soil ecology and cyanobacte-ria have been reported to accumulate and detoxify thesepesticides Previous studies demonstrated that Synechocystissp PUPCCC 64 Westiellopsis prolifica Nostoc hatei andAnabaena sphaerica are able to degrade organophosphorusor organochlorine insecticides in the aquatic environment[26 27]

One of the drawbacks that limit the practical applicationsof cyanobacteria in wastewater treatment is the difficulty inthe separationofbiomass fromtheeffluentbefore discharge [49]

The use of immobilization to entrap cyanobacteria in matri-ces (agarose carrageenan chitson alginate andpolyurethanefoam) can help to solve the harvesting problem In additionimmobilized cyanobacteria showhigher efficiency in nutrientor metal removal compared to their free-living counterpartImmobilization of Anabaena doliolumwas shown to increaseits copper and iron ions removal capacity in the order of45 and 23 higher than its free-living counterpart [23]Similarly the efficiency to take up nitrogenous and phospho-rus compounds was enhanced in immobilized Chlorella andAnabaena [23]

In natural environment many cyanobacteria form sym-biotic associations with other aerobic or anaerobic microor-ganisms It is interesting to note that cyanobacterial matsincluding Oscillatoria Synechocystis and Pleurocapsa havebeen shown to aid in the degradation of hydrocarbons presentin oil Although cyanobacteria are not directly responsiblefor the degradation of hydrocarbons they facilitated thedegradation process by providing oxygen and nutrients to theassociated oil-degrading bacteria [50] A consortium com-prising Phormidium Oscillatoria Chroococcus and the oil-degrading bacterium Burkholderia cepacia was successfullydeveloped and employed on a rotating biological contactor toefficiently degrade petroleum compounds [51]

4 Cyanobacteria as Potential BioactiveCompounds Sources

Cyanobacteria have been identified as sources of bioac-tive compounds with interesting biological activities forexample antibacterial antifungal antiviral antialgal anti-cancer anti-inflammatory and so forth These bioactivecompounds include lipopeptides (40) amino acids (56)fatty acids (42) macrolides (42) and amides (9) [4]


The excretion of bioactive compounds by cyanobacteria intothe aquatic environments is possible allelopathy strategyused by cyanobacteria to outcompete other microorgan-isms within the same ecosystem [52] These allelopathiccompounds include alkaloids cyclic peptides terpenes andvolatile organic compounds Cyanobacterial allelochemicalsare found to exhibit inhibitory effects toward the growthphotosynthesis respiration carbon uptake and enzymaticactivity of algae as well as induce oxidative stress in algae[53] To date several allelochemicals from cyanobacteria havebeen identified and they include cyanobacterin produced byScytonema hofmanni enediyne-containing photosystem IIinhibitor synthesized by Fischerella muscicola hapalindolesthat are isolated from Hapalosiphon and Fischerella spp andnostocyclamides from Nostoc sp These antialgal compoundssynthesized by cyanobacteria can be developed as alternativeto synthetic algicides that are used to control harmful algalblooms

Extensive screenings are presently undergoing to searchfor new antibacterial compounds from cyanobacterialextracts that can be potentially developed as new drugs orantibiotics It has been reported that cyanobacterial extractsof Westiellopsis prolifica ARM 365 Hapalosiphon hibernicusARM 178 Nostoc muscorum ARM 221 Fischerella sp ARM354 and Scytonema sp showed antibacterial activity againstPseudomonas striata Bacillus subtilis E coli and Bradyrhizo-bium sp [54] In another study Anabaena sp was shown toexhibit antibacterial activity against Staphylococcus aureusE coli Pseudomonas aeruginosa Salmonella typhi and Kleb-siella pneumonia [55] Noscomin a diterpenoid compoundisolated from Nostoc commune showed antibacterial activityagainst Bacillus cereus Staphylococcus epidermidis and E coliat MIC values comparable with those obtained for standarddrugs [56] Additionally cyanobacteria produce a broadspectrum of compounds with antifungal activity For exam-ple nostofungicide isolated from N commune is effectiveagainst Aspergillus candidus norharmane from Nostoc insu-lare and 441015840-dihydroxybiphenyl from Nodularia harveyanashowed potent antifungal activity against Candida albicans[57 58] Antiviral activity of extracts or compounds isolatedfrom cyanobacteria has also been reported Cyanovirin-Nscytovirin N and sulfoglycolipid isolated from Nostocellipsosporum Scytonema varium and Scytonema sprespectively are shown to exhibit potent antiviral activityagainst human immunodeficiency virus (HIV) [59ndash61]

5 Cyanobacteria as Sources ofValue-Added Products

51 Pigments Vitamins and Enzymes Cyanobacteria areknown to produce various fine chemicals and there areconsiderable interests in the production of these chemicalsfrom cyanobacteria on a commercially viable scale Twoimportant cyanobacterial pigments phycobiliproteins andcarotenoids are extensively used in bioindustry and havehigh commercial value Phycobilisomes are the major light-harvesting complexes present in cyanobacteria and theyconsist mainly of phycobiliproteins such as phycocyaninallophycocyanin and phycoerythrin On the other hand

the major carotenoids accumulated by cyanobacteria arebeta-carotene zeaxanthin nostoxanthin echinenone andcanthaxanthin These pigments are commonly used as foodcolorants food additives and supplements for human andanimal feeds Carotenoids are well known for their antioxi-dant properties and their possible role in the prevention andcontrol of human health and disease conditions for examplecancer cardiovascular problems cataracts and musculardystrophy has been reported [62]

Some marine cyanobacteria are valuable sources of vita-mins and they are being used for the large-scale production ofvitamins of commercial interest such as vitamins B and E Forexample Spirulina (Arthrospira) is known to be a rich sourceof vitamin B12 beta-carotene thiamine and riboflavin Itis marketed in the form of powder granules tablets orcapsules and commercially available Spirulina tablets containup to 244 120583g of vitamin B12 per dry weight [63] Cyanobac-teria are found to secrete a broad spectrum of enzymesthat can be exploited for commercial applications Theseindustrially important enzymes include protease amylaseand phosphatases Proteases are predominantly used for foodprocessing industries alpha-amylases are extensively used instarch industries and phosphatases and acid phosphatases arewidely used as diagnostic markers [64]

52 Isoprene Isoprene is an energy rich hydrocarbon thatis potentially a biofuel and an important feedstock in thesynthetic chemistry industry It is used industrially as thestarting material to make synthetic rubber Although iso-prene is naturally synthesized and released by many herba-ceous deciduous and conifer plants into the surroundingenvironments it is impractical to harvest isoprene from plantin large-scale The production of isoprene by photosyntheticcyanobacteria through heterologous expression of isoprenesynthase (IspS) from Pueraria montana was demonstrated[65] The accumulation of sim50120583g isoprene per g dry cellweight per day was achievable in recombinant Synechocys-tis sp PCC 6803 transformed with codon optimized IspSgene In recent work the introduction of isoprene synthasetogether with themevalonic acid pathway genes was found toincrease photosynthetic isoprene production yield to approx-imately 25-fold compared with cyanobacteria transformedwith IspS gene only [66]

53 Biopolymers Polyhydroxyalkanoate (PHA) is a typeof biodegradable polymer that can serve as substitute forpetroleum-based plastics and a biocompatible material thathas promising applications in biomedical or pharmaceuticalfield Several cyanobacteria including Aphanothece sp [67]Oscillatoria limosa [68] some species of the genus Spirulina[69 70] and the thermophilic strain Synechococcus spMA19 [71] are natural producers of PHA However thePHA yield obtained from direct photosynthetic productionin cyanobacteria is low (lt10) Nutrient-limiting cultureconditions and carbon feedstocks addition were found toenhance PHAaccumulationThe applications of phosphorus-deficiency gas-exchange limitation culture conditions as wellas fructose and acetate addition had resulted in remarkableincreases in PHA accumulation up to 38 of the dry cell


weight in Synechocystis sp PCC 6803 [72] In another attemptto enhance photosynthetic PHA production in Synechocystissp PCC 6803 the introduction of an acetoacetyl-CoA syn-thase that catalyzes the irreversible condensation of acetyl-CoA and malonyl-CoA to acetoacetyl-CoA was found tohave a positive impact on PHA production [73] The highestPHA production obtained from photosynthetic cultures ofgenetically Synechocystis sp was 14wt High PHA accu-mulation of up to 52 dry cell weight was demonstratedin marine cyanobacterium Synechococcus sp PCC 7002 TheSynechococcus sp was transformed with plasmid carryingCupriavidus necator PHAbiosynthetic genes using recA com-plementation as selection pressure for plasmid stability [74]Interestingly the ability of (S)- and (R)-3-hydroxybutyratemolecules synthesis and secretion from genetically engi-neered Synechocystis sp PCC 6803 cells was also reported[75]

6 Challenges and Outlook

Considering the great potentials of cyanobacteria in diversebiotechnological applications it would be of scientific tech-nological and industrial interests to translate theses photo-synthetic biological systemsrsquo potential into realizable large-scale production Although a broad spectrum of naturalproducts synthesized by cyanobacteria has potential bioin-dustrial applications the underlying challenge in commer-cialization is to achieve production yields that meet realisticscalable production

The potential uses of cyanobacteria as hosts for the pro-duction of various carbon-containing industrial products forexample ethanol isobutanol hydrogen gas and alkanes havebeen extensively explored for the past ten years [13 16 17 3233 39] In this productionmodel the cyanobacterial cells canbe seen as photosynthetic microbial cell factories that harvestsolar energy to fix carbon dioxide into products of interest Asthe carbon content of the synthesized compound originatesfrom the carbon dioxide fixed during photosynthesis theproductivity of the system depends on the efficiency ofcarbon dioxide fixation On the other hand photosyntheticefficiencies are affected by the efficiency of solar photoncapture and the conversion of captured photon to chemicallystored energy [33] Although cyanobacteria are equippedwith photosynthetic machineries that are two- to threefoldmore efficient in solar energy conversion than that of cropplants the efficiencies are still low with yield less than 10[9] Genetic engineering approaches aiming at improvingthe photosynthetic efficiencies of cyanobacteria that willultimately result in higher final product yield are beingexplored RuBisCo is an essential enzyme that catalyzes thefirstmajor step of carbon fixation However it is a notoriouslyinefficient enzyme that has slow catalytic rate and is subjectto competitive inhibition by O

2 RuBisCo is suggested to be

the rate-limiting enzyme in carbon fixation and a potentialtarget for genetic manipulation to improve photosyntheticefficiency [76] Overexpression of Synechococcus sp PCC6301 RuBisCo operon in S elongatus PCC 7942 was found toenhance CO

2fixation and boost isobutanol production levels

by approximately twofold in the genetically engineered strain[77]

Light availability plays pivotal role in determining thegrowth of photoautotrophs thus selective pressure hasfavored adaptations that maximize light capture in photosyn-thetic biological systems to compete for sunlight Howeverunder high light conditions the excessive capture of photonsby cells in the surface layer of cyanobacterial cultures islost through thermal dissipation limiting the availabilityof light to cells underneath To address this issue attemptto artificially reduce the light-harvesting antenna size wascarried out This strategy is designed to enable cells at theculture surface to capture only the amount of light thatthey require and allow greater penetration of excess lightinto the culture In a phycocyanin-deficient Synechocystisstrain a substantial improvement in photosynthetic activ-ity and biomass production was obtained relative to theirwild-type counterparts [78] As oxygenic photosynthesis incyanobacteria effectively utilizes photons in the waveband of400ndash700 nm the remainder of the energy is lost as heat Inaddition the photosystems in most photosynthetic organ-isms compete for solar radiation with the same wavelengthsreducing the overall energy conversion efficiency One of theinteresting strategies to increase photosynthetic efficienciessuggests the engineering of one of the two photosystems toextend the absorption maxima to sim1100 nm [79]

While biotechnological production potentials ofcyanobacteria have attracted considerable interest highyield synthesis of industrial products from cyanobacteriaremains challenging In biofuels synthesis the productionability of cyanobacteria is likely limited by the low level ofcells tolerance to biofuel RNA-sequencing was carried outto determine the transcriptome profile of Synechocystis spPCC6803 cultivated under different concentrations of exoge-nous n-butanol The study revealed that the overexpressionof several candidate proteins particularly the small heatshock protein HspA improved the tolerance of Synechocystissp to butanol [80] To understand the metabolomics changesrelated to butanol stress metabolomics profile of Synechocys-tis sp PCC 6803 cultivated under gradual increase of butanolconcentration was determinedThe identification of metabo-lites that were differentially regulated during the evolutionprocess provides metabolomics basis for further engineeringof cyanobacteria to improve their product tolerance [81]

Although most strategies implemented to engineercyanobacteria as microbial cell factories for various high-value products synthesis focus on local pathway optimizationsystem biology approaches (eg transcriptomes proteomicsand metabolomics) would enhance our understanding ofcyanobacterial biochemistry For example recent transcrip-tomes studies on genetically engineered Synechocystis spPCC 6803 provide insights into understanding the effects ofoverexpressing PHA biosynthetic genes on photoautotrophicbiopolymer production [73] Constraint-based models ofmetabolism can be used to evaluate the effects of geneticmanipulation or environmental perturbations on biomassyield andmetabolic flux distribution Based onmathematicalmodels the optimal intracellular metabolic flux profile tomaximize the value of the selected objective function can


be predicted This in silico modeling approach provides amean to design an optimal metabolic network to maximizethe synthesis of any product of interest A comprehensivegenome-scale metabolic model for Synechocystis sp PCC6803 was reconstructed and analyzed to understand the pho-tosynthetic process in cyanobacteria in mechanistic detailInterestingly the metabolic model revealed that the regula-tion of photosynthetic activity in Synechocystis sp is rathercomplex and a high degree of cooperativity between ninealternative electron flow pathways is important for optimalphotoautotrophic metabolism [82]

7 Conclusion

Owing to their simple growth requirements ease of geneticmanipulation and ability to capture solar energy and fixatmospheric carbon dioxide directly into industrial productsthe potentials of cyanobacteria for various biotechnologicalapplications have been well recognized However the appli-cation of cyanobacterial cultures for large-scale synthesisof products of interest is technologically challenging Effi-cient and cost-effective photosynthetic bioreactors need tobe developed to achieve maximum productivity in large-scale cyanobacterial cultures with minimum operation costsWith the advances in genetic and metabolic engineeringapproaches as well as development of suitable cultivationsystems we can harness the photosynthetic efficiency ofcyanobacteria to provide green paths for the synthesis ofindustrial products

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The research of the first author on cyanobacteria has beensupported by research grant (1002PCCB910206) from Uni-versiti Sains Malaysia N-S Lau gratefully acknowledges thepostdoctoral fellowship by Universiti Sains Malaysia

References

[1] S B Hedges H Chen S Kumar D Y Wang A S Thompsonand HWatanabe ldquoA genomic timescale for the origin of eukar-yotesrdquoBMCEvolutionary Biology vol 1 article 4 10 pages 2001

[2] W Loffelhardt and H Bohnert ldquoMolecular biology of cyan-ellesrdquo inTheMolecular Biology of Cyanobacteria D Bryant Edpp 65ndash89 Springer Amsterdam The Netherlands 2004

[3] BAWhitton andM Potts ldquoIntroduction to the cyanobacteriardquoin The Ecology of Cyanobacteria Their Diversity in Time andSpace B A Whitton and M Potts Eds pp 1ndash11 KluwerAcademic Dordrecht The Netherlands 2000

[4] A M Burja B Banaigs E Abou-Mansour J Grant Burgessand P C Wright ldquoMarine cyanobacteriamdasha prolific source ofnatural productsrdquo Tetrahedron vol 57 no 46 pp 9347ndash93772001

[5] L J Stal ldquoPhysiological ecology of cyanobacteria in microbialmats and other communitiesrdquo New Phytologist vol 131 no 1pp 1ndash32 1995

[6] Y Cohen B B Jorgensen N P Revsbech and R PoplawskildquoAdaptation to hydrogen sulfide of oxygenic and anoxygenicphotosynthesis among cyanobacteriardquo Applied and Environ-mental Microbiology vol 51 no 2 pp 398ndash407 1986

[7] L J Stal and R Moezelaar ldquoFermentation in cyanobacteriardquoFEMS Microbiology Reviews vol 21 no 2 pp 179ndash211 1997

[8] D G Capone J A Burns J PMontoya et al ldquoNitrogen fixationby Trichodesmium spp an important source of new nitrogen tothe tropical and subtropical North Atlantic Oceanrdquo GlobalBiogeochemical Cycles vol 19 no 2 Article IDGB2024 pp 1ndash172005

[9] G C Dismukes D Carrieri N Bennette G M Ananyev andM C Posewitz ldquoAquatic phototrophs efficient alternatives toland-based crops for biofuelsrdquo Current Opinion in Biotechnol-ogy vol 19 no 3 pp 235ndash240 2008

[10] O Koksharova and C Wolk ldquoGenetic tools for cyanobacteriardquoApplied Microbiology and Biotechnology vol 58 no 2 pp 123ndash137 2002

[11] M-D Deng and J R Coleman ldquoEthanol synthesis by geneticengineering in cyanobacteriardquo Applied and EnvironmentalMicrobiology vol 65 no 2 pp 523ndash528 1999

[12] Z Gao H Zhao Z Li X Tan and X Lu ldquoPhotosyntheticproduction of ethanol from carbon dioxide in genetically engi-neered cyanobacteriardquo Energy amp Environmental Science vol 5no 12 pp 9857ndash9865 2012

[13] S Atsumi T Hanai and J C Liao ldquoNon-fermentative pathwaysfor synthesis of branched-chain higher alcohols as biofuelsrdquoNature vol 451 no 7174 pp 86ndash89 2008

[14] E I Lan and J C Liao ldquoATP drives direct photosyntheticproduction of 1-butanol in cyanobacteriardquo Proceedings of theNational Academy of Sciences of the United States of Americavol 109 no 16 pp 6018ndash6023 2012

[15] H Masukawa K Nakamura M Mochimaru and H SakuraildquoPhotobiological hydrogen production and nitrogenase activityin some heterocystous cyanobacteriardquo in Biohydrogen II JMiyake T Matsunaga and A San Pietro Eds pp 63ndash66Elsevier Oxford UK 2001

[16] D C Ducat G Sachdeva and P A Silver ldquoRewiring hydro-genase-dependent redox circuits in cyanobacteriardquo Proceedingsof the National Academy of Sciences of the United States ofAmerica vol 108 no 10 pp 3941ndash3946 2011

[17] N B Reppas and C P RidleyMethods and Compositions for theRecombinant Biosynthesis of n-Alkanes Joule Unlimited 2010

[18] X Liu J Sheng and R Curtiss III ldquoFatty acid production ingenetically modified cyanobacteriardquo Proceedings of the NationalAcademy of Sciences of the United States of America vol 108 no17 pp 6899ndash6904 2011

[19] R Blier G Laliberte and J de la Noue ldquoTertiary treatment ofcheese factory anaerobic effluent with Phormidium bohneri andMicractinumpusillumrdquoBioresource Technology vol 52 no 2 pp151ndash155 1995

[20] J de la Noue and A Basseres ldquoBiotreatment of anaerobicallydigested swine manure with microalgaerdquo Biological Wastes vol29 no 1 pp 17ndash31 1989

[21] S Hashimoto and K Furukawa ldquoNutrient removal from sec-ondary effluent by filamentous algaerdquo Journal of Fermentationand Bioengineering vol 67 no 1 pp 62ndash69 1989


[22] S Balaji T Kalaivani and C Rajasekaran ldquoBiosorption of zincand nickel and its effect on growth of different Spirulina strainsrdquoCLEANmdashSoil Air Water vol 42 no 4 pp 507ndash512 2014

[23] L C Rai and N Mallick ldquoRemoval and assessment of toxicityof Cu and Fe toAnabaena doliolum and Chlorella vulgaris usingfree and immobilized cellsrdquo World Journal of Microbiology ampBiotechnology vol 8 no 2 pp 110ndash114 1992

[24] G Colica P C Mecarozzi and R De Philippis ldquoTreatmentof Cr(VI)-containing wastewaters with exopolysaccharide-producing cyanobacteria in pilot flow through and batchsystemsrdquo Applied Microbiology and Biotechnology vol 87 no 5pp 1953ndash1961 2010

[25] E El-Bestawy ldquoTreatment of mixed domestic-industrial waste-water using cyanobacteriardquo Journal of Industrial Microbiologyand Biotechnology vol 35 no 11 pp 1503ndash1516 2008

[26] M N Jha and S K Mishra ldquoBiological responses of cyanobac-teria to insecticides and their insecticide degrading potentialrdquoBulletin of Environmental Contamination and Toxicology vol75 no 2 pp 374ndash381 2005

[27] D P Singh J I S Khattar J Nadda et al ldquoChlorpyrifosdegradation by the cyanobacterium Synechocystis sp strainPUPCCC 64rdquo Environmental Science and Pollution Researchvol 18 no 8 pp 1351ndash1359 2011

[28] D P Singh J I S Khattar M Kaur G Kaur M Gupta andY Singh ldquoAnilofos tolerance and its mineralization by thecyanobacterium Synechocystis sp strain PUPCCC 64rdquo PLoSONE vol 8 no 1 Article ID e53445 2013

[29] WM IbrahimMA Karam RM El-Shahat andA A AdwayldquoBiodegradation and utilization of organophosphorus pesticidemalathion by cyanobacteriardquo BioMed Research Internationalvol 2014 Article ID 392682 6 pages 2014

[30] G Stephanopoulos ldquoChallenges in engineering microbes forbiofuels productionrdquo Science vol 315 no 5813 pp 801ndash8042007

[31] GW Huber S Iborra and A Corma ldquoSynthesis of transporta-tion fuels from biomass chemistry catalysts and engineeringrdquoChemical Reviews vol 106 no 9 pp 4044ndash4098 2006

[32] J Dexter and P Fu ldquoMetabolic engineering of cyanobacteria forethanol productionrdquoEnergyampEnvironmental Science vol 2 no8 pp 857ndash864 2009

[33] D C Ducat J C Way and P A Silver ldquoEngineering cyanobac-teria to generate high-value productsrdquo Trends in Biotechnologyvol 29 no 2 pp 95ndash103 2011

[34] G R Lambert andGD Smith ldquoHydrogen formation bymarineblue-green algaerdquo FEBS Letters vol 83 no 1 pp 159ndash162 1977

[35] M Chen J Li L Zhang et al ldquoAuto-flotation of hetero-cyst enables the efficient production of renewable energy incyanobacteriardquo Scientific Reports vol 4 Article ID 03998 2014

[36] H Leino S Shunmugam J Isojarvi et al ldquoCharacterization oftenH

2producing cyanobacteria isolated from theBaltic Sea and

Finnish lakesrdquo International Journal of Hydrogen Energy vol 39no 17 pp 8983ndash8991 2014

[37] P Tamagnini R Axelsson P Lindberg F Oxelfelt RWunschi-ers and P Lindblad ldquoHydrogenases and hydrogen metabolismof cyanobacteriardquoMicrobiology and Molecular Biology Reviewsvol 66 no 1 pp 1ndash20 2002

[38] M L Ghirardi M C Posewitz P-C Maness A Dubini J YuandM Seibert ldquoHydrogenases and hydrogen photoproductionin oxygenic photosynthetic organismsrdquo Annual Review of PlantBiology vol 58 pp 71ndash91 2007

[39] K McNeely Y Xu N Bennette D A Bryant and G C Dis-mukes ldquoRedirecting reductant flux into hydrogen productionvia metabolic engineering of fermentative carbon metabolismin a cyanobacteriumrdquoApplied and Environmental Microbiologyvol 76 no 15 pp 5032ndash5038 2010

[40] G K Kumaraswamy T Guerra X Qian S Zhang D A Bryantand G C Dismukes ldquoReprogramming the glycolytic pathwayfor increased hydrogen production in cyanobacteria Metabolicengineering of NAD+-dependent GAPDHrdquo Energy amp Environ-mental Science vol 6 no 12 pp 3722ndash3731 2013

[41] D Mendez-Perez M B Begemann and B F Pfleger ldquoModularsynthase-encoding gene involved in 120572-olefin biosynthesis inSynechococcus sp strain pcC 7002rdquo Applied and EnvironmentalMicrobiology vol 77 no 12 pp 4264ndash4267 2011

[42] E J Steen Y Kang G Bokinsky et al ldquoMicrobial productionof fatty-acid-derived fuels and chemicals from plant biomassrdquoNature vol 463 no 7280 pp 559ndash562 2010

[43] A Schirmer M A Rude X Li E Popova and S B delCardayre ldquoMicrobial biosynthesis of alkanesrdquo Science vol 329no 5991 pp 559ndash562 2010

[44] W Wang X Liu and X Lu ldquoEngineering cyanobacteria toimprove photosynthetic production of alka(e)nesrdquo Biotechnol-ogy for Biofuels vol 6 no 1 article 69 2013

[45] B K Kaiser M Carleton J W Hickman et al ldquoFatty aldehydesin cyanobacteria are a metabolically flexible precursor for adiversity of biofuel productsrdquo PLoS ONE vol 8 no 3 ArticleID e58307 2013

[46] T Yoshino Y Liang D Arai et al ldquoAlkane production by themarine cyanobacterium Synechococcus sp NKBG15041c pos-sessing the120572-olefin biosynthesis pathwayrdquoAppliedMicrobiologyand Biotechnology vol 99 no 3 pp 1521ndash1529 2015

[47] H Mohapatra and R Gupta ldquoConcurrent sorption of Zn(II)Cu(II) and Co(II) by Oscillatoria angustissima as a functionof pH in binary and ternary metal solutionsrdquo BioresourceTechnology vol 96 no 12 pp 1387ndash1398 2005

[48] Y Pouliot G Buelna C Racine and J de la Noue ldquoCulture ofcyanobacteria for tertiary wastewater treatment and biomassproductionrdquo Biological Wastes vol 29 no 2 pp 81ndash91 1989

[49] S Vijayakumar ldquoPotential applications of cyanobacteria inindustrial effluentsmdasha reviewrdquo Journal of Bioremediation ampBiodegradation vol 3 no 6 p 154 2012

[50] R M M Abed S Dobretsov and K Sudesh ldquoApplications ofcyanobacteria in biotechnologyrdquo Journal of Applied Microbiol-ogy vol 106 no 1 pp 1ndash12 2009

[51] R M M Abed and J Koster ldquoThe direct role of aerobicheterotrophic bacteria associated with cyanobacteria in thedegradation of oil compoundsrdquo International Biodeteriorationand Biodegradation vol 55 no 1 pp 29ndash37 2005

[52] E M Gross ldquoAllelopathy of aquatic autotrophsrdquo CriticalReviews in Plant Sciences vol 22 no 3-4 pp 313ndash339 2003

[53] H-U Dahms X Ying and C Pfeiffer ldquoAntifouling potential ofcyanobacteria a mini-reviewrdquo Biofouling vol 22 no 5 pp 317ndash327 2006

[54] R Tyagi B D Kaushik and J Kumar ldquoAntimicrobial activity ofsome cyanobacteriardquo in Microbial Diversity and Biotechnologyin Food Security R N Kharwar R S Upadhyay N K Dubeyand R Raghuwanshi Eds pp 463ndash470 Springer New DelhiIndia 2014

[55] A Chauhan G Chauhan P C Gupta P Goyal and P KaushikldquoIn vitro antibacterial evaluation ofAnabaena sp against severalclinically significantmicroflora andHPTLCanalysis of its active


crude extractsrdquo Indian Journal of Pharmacology vol 42 no 2pp 105ndash107 2010

[56] B Jaki J Orjala and O Sticher ldquoA novel extracellular diter-penoid with antibacterial activity from the cyanobacteriumNostoc communerdquo Journal of Natural Products vol 62 no 3 pp502ndash503 1999

[57] S-I Kajiyama H Kanzaki K Kawazu and A KobayashildquoNostofungicidine an antifungal lipopeptide from the field-grown terrestrial blue-green algaNostoc communerdquoTetrahedronLetters vol 39 no 22 pp 3737ndash3740 1998

[58] R-B Volk ldquoScreening of microalgal culture media for the pres-ence of algicidal compounds and isolation and identificationof two bioactive metabolites excreted by the cyanobacteriaNostoc insulare and Nodularia harveyanardquo Journal of AppliedPhycology vol 17 no 4 pp 339ndash347 2005

[59] M R Boyd K R Gustafson J B McMahon et al ldquoDiscoveryof cyanovirin-N a novel human immunodeficiency virus-inactivating protein that binds viral surface envelope glycopro-tein gp120 potential applications to microbicide developmentrdquoAntimicrobial Agents and Chemotherapy vol 41 no 7 pp 1521ndash1530 1997

[60] H R Bokesch B R OrsquoKeefe T C McKee et al ldquoA potent novelanti-HIV protein from the cultured cyanobacterium Scytonemavariumrdquo Biochemistry vol 42 no 9 pp 2578ndash2584 2003

[61] S Loya V Reshef E Mizrachi et al ldquoThe inhibition of thereverse transcriptase of HIV-1 by the natural sulfoglycolipidsfrom cyanobacteria contribution of different moieties to theirhigh potencyrdquo Journal of Natural Products vol 61 no 7 pp 891ndash895 1998

[62] A C Guedes H M Amaro and F X Malcata ldquoMicroalgae assources of carotenoidsrdquoMarineDrugs vol 9 no 4 pp 625ndash6442011

[63] F Watanabe H Katsura S Takenaka et al ldquoPseudovitamin B12

is the predominant cobamide of an algal health food spirulinatabletsrdquo Journal of Agricultural and Food Chemistry vol 47 no11 pp 4736ndash4741 1999

[64] V Padmapriya and N Anand ldquoEvaluation of some industriallyimportant enzymes in filamentous cyanobacteriardquo ARPN Jour-nal of Agricultural and Biological Science vol 5 no 5 pp 86ndash972010

[65] P Lindberg S Park and A Melis ldquoEngineering a platform forphotosynthetic isoprene production in cyanobacteria usingSynechocystis as the model organismrdquo Metabolic Engineeringvol 12 no 1 pp 70ndash79 2010

[66] F K Bentley A Zurbriggen and A Melis ldquoHeterologousexpression of the mevalonic acid pathway in cyanobacteriaenhances endogenous carbon partitioning to isoprenerdquoMolec-ular Plant vol 7 no 1 pp 71ndash86 2014

[67] R J Capon R W Dunlop E L Ghisalberti and P R JefferiesldquoPoly-3-hydroxyalkanoates from marine and freshwatercyanobacteriardquo Phytochemistry vol 22 no 5 pp 1181ndash11841983

[68] L J Stal H Heyer and G Jacobs ldquoOccurrence and roleof poly-hydroxy-alkanoate in the cyanobacterium Oscillatorialimosardquo in Novel Biodegradable Microbial Polymers pp 435ndash438 Springer 1990

[69] J Campbell III S E Stevens Jr and D L Balkwill ldquoAccumula-tion of poly-120573-hydroxybutyrate in Spirulina platensisrdquo Journalof Bacteriology vol 149 no 1 pp 361ndash363 1982

[70] M Vincenzini C Sili R de Philippis A Ena and R MaterassildquoOccurrence of poly-120573-hydroxybutyrate in Spirulina speciesrdquoJournal of Bacteriology vol 172 no 5 pp 2791ndash2792 1990

[71] M Miyake M Erata and Y Asada ldquoA thermophilic cyanobac-terium Synechococcus sp MA19 capable of accumulating poly-120573-hydroxybutyraterdquo Journal of Fermentation and Bioengineer-ing vol 82 no 5 pp 512ndash514 1996

[72] B Panda and N Mallick ldquoEnhanced poly-120573-hydroxybutyrateaccumulation in a unicellular cyanobacterium Synechocystis spPCC 6803rdquo Letters in Applied Microbiology vol 44 no 2 pp194ndash198 2007

[73] N-S Lau C P Foong Y Kurihara K Sudesh and MMatsui ldquoRNA-seq Analysis provides insights for understandingphotoautotrophic polyhydroxyalkanoate production in recom-binant Synechocystis sprdquo PLoS ONE vol 9 no 1 Article IDe86368 2014

[74] H Akiyama H Okuhata T Onizuka et al ldquoAntibiotics-freestable polyhydroxyalkanoate (PHA) production from carbondioxide by recombinant cyanobacteriardquo Bioresource Technologyvol 102 no 23 pp 11039ndash11042 2011

[75] BWang S Pugh D R Nielsen W Zhang and D R MeldrumldquoEngineering cyanobacteria for photosynthetic production of 3-hydroxybutyrate directly fromCO

2rdquoMetabolic Engineering vol

16 no 1 pp 68ndash77 2013[76] R J Spreitzer andM E Salvucci ldquoRubisco structure regulatory

interactions and possibilities for a better enzymerdquo AnnualReview of Plant Biology vol 53 pp 449ndash475 2002

[77] S Atsumi W Higashide and J C Liao ldquoDirect photosyn-thetic recycling of carbon dioxide to isobutyraldehyderdquo NatureBiotechnology vol 27 no 12 pp 1177ndash1180 2009

[78] H Kirst C Formighieri and A Melis ldquoMaximizing photosyn-thetic efficiency and culture productivity in cyanobacteria uponminimizing the phycobilisome light-harvesting antenna sizerdquoBiochimica et Biophysica ActamdashBioenergetics vol 1837 no 10pp 1653ndash1664 2014

[79] R E Blankenship D M Tiede J Barber et al ldquoComparingphotosynthetic and photovoltaic efficiencies and recognizingthe potential for improvementrdquo Science vol 332 no 6031 pp805ndash809 2011

[80] J Anfelt B Hallstrom J Nielsen M Uhlen and E P Hud-son ldquoUsing transcriptomics to improve butanol tolerance ofSynechocystis sp strain PCC 6803rdquo Applied and EnvironmentalMicrobiology vol 79 no 23 pp 7419ndash7427 2013

[81] Y Wang M Shi X Niu et al ldquoMetabolomic basis of laboratoryevolution of butanol tolerance in photosynthetic Synechocystissp PCC 6803rdquoMicrobial Cell Factories vol 13 article 151 2014

[82] J Nogales S Gudmundsson E M Knight B O Palssonand I Thiele ldquoDetailing the optimality of photosynthesis incyanobacteria through systems biology analysisrdquo Proceedings ofthe National Academy of Sciences of the United States of Americavol 109 no 7 pp 2678ndash2683 2012

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Anatomy Research International

PeptidesInternational Journal of


Hindawi Publishing Corporation httpwwwhindawicom

International Journal of

Volume 2014

Zoology


Molecular Biology International

GenomicsInternational Journal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


BioinformaticsAdvances in

Marine BiologyJournal of



Signal TransductionJournal of


BioMed Research International

Evolutionary BiologyInternational Journal of



Biochemistry Research International

ArchaeaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014


Genetics Research International


Advances in

Virolog y

Hindawi Publishing Corporationhttpwwwhindawicom

Nucleic AcidsJournal of

Volume 2014

Stem CellsInternational



Enzyme Research



Microbiology


of carbon sources and complex growth media Sunlight is themost readily available and inexpensive resource on earth andthe use of cyanobacteria for the production of fine chemicalsand biofuels from solar energy offers a greener path for thesynthesis process Equipped with superior photosynthesiscapabilities cyanobacteria have higher photosynthesis andbiomass production rates compared to plants and can convertup to 3ndash9 of the solar energy into biomass compared tole025ndash3 achieved by crops for example corn sugar cane[9] They also require less land area for cultivation thanterrestrial plant reducing the competition for arable landwith crops intended for human consumption Cyanobacteriautilize carbon dioxide a type of greenhouse gases duringphotosynthesis and help to achieve a carbon neutral pro-duction process Being prokaryotes cyanobacteria possessrelatively simple genetic background that eases manipulation[10] In addition the residual cyanobacteria biomasses thatare left over after high-value products extraction can be usedas animal feed or converted into organic fertilizer

Considering the aforementioned inherent merits ofcyanobacteria they are one of the attractive candidates foruse in diverse biotechnological application With the recentadvances in genetic and metabolic engineering technologiesand the availability of more than 300 cyanobacterial genomesequences there is significant progress in research directedtowards realizing the full potential of these photosyntheticbacteria Cyanobacteria have gained considerable attention inrecent years for their possible use in agriculture nutraceu-ticals effluent treatment and the production of biofuelsvarious secondary metabolites including vitamins toxinsand enzymes In this paper the recent progress in developingcyanobacteria for various potential applications in biotech-nology is discussed

2 Potential Applications of Cyanobacteria asEnergy Sources

Anticipation of depletion of fossil fuel resources and globalwarming have spurred vigorous research initiatives aimedat developing carbon neutral alternatives to supplement orreplace fossil fuels Several alternatives to current fossil fuelshave been proposed and they include ethanol 1-butanolisobutanol hydrogen gas and alkanes

The production of ethanol via biological route hasreceived widespread attention in recent years Traditionallya two-step route to first collect plant-derived biomass andsubsequent conversion of the biomass to fuels by microbialfermentation is employed [30] This indirect productionscheme is inefficient in the conversion of biomass to fuels[31] and thus there are increasing interests in the use ofphotosynthetic microbes to directly convert carbon dioxideto fuels Although some cyanobacterial strains naturallyproduce low level of ethanol as a byproduct of naturalfermentation it is necessary to enhance the production effi-ciency of cyanobacteria to reach an economically viable levelAn attempt to introduce the pyruvate decarboxylase (pdc)and alcohol dehydrogenase II (adh) genes from Zymomonasmobilis into the chromosome of Synechocystis sp PCC 6803was reported [11] (Figure 1) Photosynthetic production of

up to 550mgL ethanol was achieved in the engineeredSynechocystis sp [32] Further engineering of Synechocystissp by overexpressing endogenous alcohol dehydrogenaseand disrupting polyhydroxyalkanoate biosynthetic pathwayincreased ethanol production up to 5500mgL [12] (Table 1)Isobutanol and 1-butanol are considered as better substitutesfor gasoline compared to ethanol as they have greater energydensity being less corrosive and less volatile [33] Using asimilar genetic modification approach direct photosyntheticproduction of isobutanol in cyanobacteria is also feasibleTheintroduction of an artificial isobutanol biosynthesis pathwayinto Synechococcus elongatus PCC 7942 had resulted in theproduction of isobutyraldehyde and isobutanol up to 1100 and450mgL respectively [13]

More than 14 genera of cyanobacteria are known toproduce hydrogen under various culture conditions and theyinclude Anabaena Aphanocapsa CalothrixMicrocystisNos-toc andOscillatoria [15 34ndash36] In heterocystous or filamen-tous cyanobacteria hydrogen gas is produced as a byproductof nitrogen fixation under nitrogen limiting growth con-ditions In cyanobacteria the production of hydrogen gasis also facilitated by the reversible activity of hydrogenasesenzymes Two distinct types of hydrogenases are present indifferent cyanobacterial species uptake hydrogenases thatoxidize oxygen bidirectional or reversible hydrogenases thatcan both take up or produce hydrogen [37] The efficiencyof hydrogen production in some cyanobacteria is limitedby the extreme oxygen sensitivity of hydrogenases and thetendency for [NiFe] hydrogenases to thermodynamicallyfavor hydrogen uptake [38] Increased production of hydro-gen is achievable by blocking pathways that compete forreductant consumption with hydrogenases The disruptionof ldhA gene that is responsible for NADH consumptionin lactate production in Synechococcus sp PCC 7002 hadresulted in a significant increase in the NADHNAD+ ratioand a concomitant fivefold increase in hydrogen produc-tion by the native bidirectional [NiFe] hydrogenase [39]In another example enhanced hydrogen production in Selongatus PCC 7942 was obtained through heterologousexpression of exogenous [FeFe] hydrogenases (HydA) fromClostridium acetobutylicum [16] The expression of [FeFe]hydrogenases that thermodynamically favor hydrogen pro-duction relative to [NiFe] hydrogenase can modulate redoxflux in the heterologous host resulting in higher hydrogenproduction Metabolic engineering of cyanobacteria by redi-recting glycogen catabolism through the oxidative pentosepathway was found to enhance intracellular NADPH con-centrations and consequently improve the hydrogen yieldIn the glyceraldehyde-3-phosphate (gap1) gene deletion andNAD+-glyceraldehyde-3-phosphate (GAPDH-1) overexpres-sion strains of Synechococcus sp PCC 7002 23-fold and3-fold increase in hydrogen production respectively wereobtained compared to the wild type [40]

Some cyanobacteria are known to synthesize alkanesor alkenes that have desirable properties for combustionStudies on the alkane biosynthetic pathways in cyanobacteriarevealed that the two important enzymes acyl-acyl carrierprotein reductase and aldehyde decarbonylase are responsi-ble for the conversion of fatty acid metabolism intermediates


3-PGA

G3P

F6P

RuBP Calvin cycle

PEP

Pyruvate

DXP

HMBPP DMAPP

Acetaldehyde


Acetyl-CoA


Isoprene

Ethanol

Isobutanol

PHB

Alkanesaar adc

adh

kivd

ispS

alsS ilvC ilvD

NADPH

FNR

FdHydrogen gashydA

PSII PSI

Light Light

adh

pdc

eminus

H+H2O

Ctb6f

CO2

2H++ 12O2









3

minus and PO4


4

+ and PO4


3

minus and PO4


3

minus and PO4

3minus



+ andNO3

minus[23]






endosulfan [27]

































7 Conclusion




Acknowledgments


References


































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology


3-PGA

G3P

F6P

RuBP Calvin cycle

PEP

Pyruvate

DXP

HMBPP DMAPP

Acetaldehyde


Acetyl-CoA


Isoprene

Ethanol

Isobutanol

PHB

Alkanesaar adc

adh

kivd

ispS

alsS ilvC ilvD

NADPH

FNR

FdHydrogen gashydA

PSII PSI

Light Light

adh

pdc

eminus

H+H2O

Ctb6f

CO2

2H++ 12O2









3

minus and PO4


4

+ and PO4


3

minus and PO4


3

minus and PO4

3minus



+ andNO3

minus[23]






endosulfan [27]

































7 Conclusion




Acknowledgments


References


































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology




3

minus and PO4


4

+ and PO4


3

minus and PO4


3

minus and PO4

3minus



+ andNO3

minus[23]






endosulfan [27]

































7 Conclusion




Acknowledgments


References


































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology
























7 Conclusion




Acknowledgments


References


































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology















7 Conclusion




Acknowledgments


References


































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology



7 Conclusion




Acknowledgments


References


































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology













































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology








































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology








Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology

Documents

Review Article Cyanobacteria: Photoautotrophic …downloads.hindawi.com/journals/bmri/2015/754934.pdfReview Article Cyanobacteria: Photoautotrophic Microbial Factories for the Sustainable