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Chapter 15 (1)
Bacteria:The Proteobacteria
I. The Phylogeny of Bacteria
15.1 Phylogenetic Overview of Bacteria
Major Lineages (Phyla) of Bacteria
15.1 Phylogenetic Overview of Bacteria
Proteobacteria
A major lineage (phyla) of Bacteria
Includes many of the most commonly encountered bacteria
Most metabolically diverse of all Bacteria
e.g., chemolithotrophy, chemoorganotrophy, phototrophy
Morphologically diverse
Divided into five classes
Alpha-, Beta-, Delta-, Gamma-, Epsilon-
Major Genera of Proteobacteria
Major Genera of Proteobacteria
II. Phototrophs, Chemolithotrophs, and Methanotrophs
15.2 Purple Phototrophic Bacteria
15.3 The Nitrifying Bacteria
15.4 Sulfur- and Iron-Oxidizing Bacteria
15.5 Hydrogen-Oxidizing Bacteria
15.6 Methanotrophs and Methylotrophs
15.2 Purple Phototrophic Bacteria
Purple Phototrophic Bacteria
Carry out anoxygenic photosynthesis; no O2 evolved
Morphologically diverse group
Genera fall within the Alpha-, Beta-, or
Gammaproteobacteria
Contain bacteriochlorophylls and carotenoid pigments
Produce intracytoplasmic photosynthetic membranes
with varying morphologies
- allow the bacteria to increase pigment content
- originate from invaginations of cytoplasmic membrane
Liquid Cultures of Phototrophic Purple Bacteria
Carotenoidless mutant
Rhodospirillum rubrum Rhodobacter sphaeroides
Lacks one of the carotenoids
Rhodopila globiformis
Membrane Systems of Phototrophic Purple Bacteria
Ectothiorhodospira mobilis
Allochromatium vinosum
Purple Sulfur Bacteria
Use hydrogen sulfide (H2S) as an electron donor for
CO2 reduction in photosynthesis
Sulfide oxidized to elemental sulfur (So) that is stored
as globules either inside or outside cells
Sulfur later disappears as it is oxidized to sulfate (SO42-)
Photomicrographs of Purple Sulfur Bacteria
Chromatium okenii Thiospirillum jenense
Thiopedia rosea Ectothiorhodospira mobilis
Purple Sulfur Bacteria (cont’d)
Many can also use other reduced sulfur compounds,
such as thiosulfate (S2O32-)
All are Gammaproteobacteria
Found in illuminated anoxic zones of lakes and other
aquatic habitats where H2S accumulates, as well as
sulfur springs
Genera and Characteristics of Purple Sulfur Bacteria
Genera and Characteristics of Purple Sulfur Bacteria
Genera and Characteristics of Purple Sulfur Bacteria
Blooms of Purple Sulfur Bacteria
Lamprocystis roseopersicina Algae (Spirogyra)
Chromatium sp.
Thiocystis sp.
Purple Nonsulfur Bacteria
Originally thought organisms were unable to use sulfide as
an electron donor for CO2 reduction, now know most can
Most can grow aerobically in the dark as
chemoorganotrophs
Some can also grow anaerobically in the dark using
fermentative or anaerobic respiration
Most can grow photoheterotrophically using light as an
energy source and organic compounds as a carbon source
All in Alpha- and Betaproteobacteria
Representatives of Purple Nonsulfur Bacteria
Phaeospirillum fulvum Rhodoblastus acidophilus Rhodobacter sphaeoides
Representatives of Purple Nonsulfur Bacteria
Rhodopila globiformis Rhodocyclus purpureus Rhodomicrobium vannielii
Genera and Characteristics of Purple Nonsulfur Bacteria
Genera and Characteristics of Purple Nonsulfur Bacteria
15.3 The Nitrifying Bacteria
Nitrifying Bacteria
Able to grow chemolithotrophically at the expense of
reduced inorganic nitrogen compounds
Found in Alpha-, Beta-, Gamma-, and Deltaproteobacteria
Nitrification (oxidation of ammonia to nitrate) occurs as two
separate reactions by different groups of bacteria
Ammonia oxidizers (nitrosifyers) (e.g., Nitrosococcus)
Nitrite oxidizer (e.g., Nitrobacter)
Photomicrographs of Nitrosifyer Nitrosococcus oceani
Phase-contrast micrograph Electron micrograph
Photomicrographs of the Nitrifyer Nitrobacter winogradskyi
Phase-contrast micrograph Electron micrograph
Nitrifying Bacteria (cont’d)
Many species have internal membrane systems that
house key enzymes in nitrification
Ammonia monooxygenase: oxidizes NH3 to NH2OH
Nitrite oxidase: oxidizes NO2- to NO3
-
* Hydroxylamine oxidoreductase
- oxidizes NH2OH to NO2-
- attached to the periplasmic face of cytoplasmic
membrane
Nitrifying Bacteria (cont’d)
Widespread in soil and water
Highest numbers in habitats with large amounts of
ammonia
i.e., sites with extensive protein decomposition and sewage
treatment facilities
Most are obligate chemolithotrophs and aerobes
One exception is anammox organisms, which oxidize
ammonia anaerobically (NH4+ + NO2
- → N2 + 2H2O)
Characteristics of the Nitrifying Bacteria
15.4 Sulfur- and Iron-Oxidizing Bacteria
Sulfur-Oxidizing Bacteria
Grow chemolithotrophically on reduced sulfur
compounds
Two broad classes
Neutrophiles
Acidophiles
Some acidophiles able to use ferrous iron (Fe2+)
Sulfur-Oxidizing Bacteria (cont’d)
Thiobacillus and close relatives are best studied
Rod-shaped
Sulfur compounds most commonly used as electron
donors are H2S, So, S2O32-; generates sulfuric acid
Achromatium
Common in freshwater sediments
Spherical cells
Pylogenetically related to purple bacteria Chromatium
* Some obligate chemolithotrophs possess special
structures that house Calvin cycle enyzmes
(carboxysomes)
Nonfilamentous Sulfur Chemolithotrophs
Halothiobacillus neapolitanus
Achromatium sp.
carboxysomes
Elemental sulfur
Calcium carbonate(CaCO3)
Sulfur-Oxidizing Bacteria (cont’d)
Beggiatoa
Filamentous, gliding bacteria
Found in habitats rich in H2S
e.g., sulfur springs, decaying seaweed beds, mud layers
of lakes, sewage polluted waters, and hydrothermal vents
Most grow mixotrophically
with reduced sulfur compounds as electron donors
and organic compounds as carbon sources ( lack ∵
Calvin cycle enzymes)
Filamentous Sulfur-Oxidizing Bacteria
Beggiatoa sp.
Sulfur-Oxidizing Bacteria (cont’d)
Thioploca
Large, filamentous sulfur-oxidizing bacteria that form cell
bundles surrounded by a common sheath
Thick mats found on ocean floor off Chile and Peru
Couple anoxic oxidation of H2S with reduction of NO3- to
NH4+
Cells of a Large Marine Thioploca Species
Thioploca sp.
Sulfur-Oxidizing Bacteria (cont’d)
Thiothrix
Filamentous sulfur-oxidizing bacteria in which filaments
group together at their ends by a holdfast to form
cellular arrangements called rosettes
Obligate aerobic mixotrophs
Thiothrix
Physiological Characteristics of Sulfur Oxidizers
15.5 Hydrogen-Oxidizing Bacteria
Hydrogen-Oxidizing Bacteria:
Most can grow autotrophically with H2 as sole electron
donor and O2 as electron acceptor (“knallgas” reaction)
Both gram-negative and gram-positive representatives
known
Contain one or more hydrogenase enzymes that
function to bind H2 and use it to either produce ATP or
for reducing power for autotrophic growth
Hydrogen-Oxidizing Bacteria (cont’d)
Most are facultative chemolithotrophs and can grow
chemoorganotrophically
Some can grow on carbon monoxide (CO) as electron
donor (carboxydotrophs; carboxydobacteria)
Hydrogen Bacteria
Ralstonia eutropha
Characteristics of Common Hydrogen-Oxidizing Bacteria
15.6 Methanotrophs and Methylotrophs
Methylotrophs
Organisms that can grow using carbon compounds
that lack C-C bonds
Most are also methanotrophs
Methanotrophs
Use CH4 and a few other one-carbon (C1) compounds
as electron donors and source of carbon
Widespread in soil and water
Obligate aerobes
Morphologically diverse
Substrates Used by Methylotrophic Bacteria
C1 metabolism of methanotrophs
Methane monooxygenase
Incorporates an atom of oxygen from O2 into methane to
produce methanol
Methanotrophs contain large amounts of sterols
Classification of methanotrophs
Two major groups
Type I
Type II
Contain extensive internal membrane systems for
methane oxidation
Electron Micrographs of Methanotrophs
Methylosinus sp. (type II) Methylococcus capsulatus (type I)
Type I methanotrophs
Assimilate C1 compounds via the ribulose
monophosphate cycle
Gammaproteobacteria
Membranes arranged as bundles of disc-shaped
vesicles
Lack complete citric acid cycle
Obligate methylotrophs
Type II methanotrophs
Assimilate C1 compounds via the serine pathway
Alphaproteobacteria
Paired membranes that run along periphery of cell
Some Characteristics of Methanotrophic Bacteria
Ecolony and Isolation of Methanotrophs
Widespread in aquatic and terrestrial environments
Methane monooxygenase also oxidizes ammonia;
competitive interaction between substrates
Certain marine mussels have symbiotic relationships
with methanotrophs
Methanotrophic Symbionts of Marine Mussels
III. Aerobic and Facultatively Aerobic Chemoorganotrophs
15.7 Pseudomonas and the Pseudomonads
15.8 Acetic Acid Bacteria
15.9 Free-Living Aerobic Nitrogen-Fixing Bacteria
15.10 Neisseria, Chromobacterium, and Relatives
15.11 Enteric Bacteria
15.12 Vibrio, Alivibrio, and Photobacterium
15.13 Rickettsias
15.7 Pseudomonas and the Pseudomonads
All genera within the pseudomonad group are
Straight or curved rods with polar flagella
Chemoorganotrophs
Obligate aerobes
Typical Pseudomonad Colonies and Cell Morphology
Burkholderia cepacia
Typical Pseudomonad Colonies and Cell Morphology
Pseudomonas sp.
Characteristics of Pseudomonads
Species of the genus Pseudomonas and related
genera can be defined on the basis of phylogeny and
physiological characteristics
Subgroups and Characteristics of Pseudomonads
Pseudomonads
Nutritionally versatile
Ecologically important organisms in water and soil
Some species are pathogenic
Includes human opportunistic pathogens and plant
pathogens
Pathogenic Pseudomonads
Zymomonas
Genus of large, gram-negative rods that carry out
vigorous fermentation of sugars to ethanol
Used in production of fermented beverages
Sugar metabolism: Entner-Doudoroff pathway
15.8 Acetic Acid Bacteria
Acetic Acid Bacteria
Organisms that carry out incomplete oxidation of
alcohols and sugars
Leads to the accumulation of organic acids as end
products
Motile rods
Aerobic
High tolerance to acidic conditions
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Acetic Acid Bacteria (cont’d)
Commonly found in alcoholic juices
Used in production of vinegar
Some can synthesize cellulose (Acetobacter xylinum)
Colonies can be identified on CaCO3 agar plates
containing ethanol
Acetobacter: peritrichously flagellated, overoxidizer
Gluconobacter: polarly flagellated, underoxidized
Colonies of Acetobacter aceti on Calcium Carbonate Agar
15.9 Free-Living Aerobic Nitrogen-Fixing Bacteria
A variety of soil microbes are capable of fixing N2
aerobically
Genera of Free-Living Aerobic Nitrogen-Fixing Bacteria
Genera of Free-Living Aerobic Nitrogen-Fixing Bacteria
Genera of Free-Living Aerobic Nitrogen-Fixing Bacteria
The major genera of bacteria capable of fixing N2
nonsymbiotically are Azotobacter, Azospirillium,
and Beijerinckia
Azotobacter are large, obligately aerobic rods; can
form resting structures (cysts)
All genera produce extensive capsules or slime layers;
believed to be important in protecting nitrogenase from
O2
Azotobacter vinelandii
Vegitive cells Cysts
Examples of Slime Production by Nitrogen2-fixing Bacteria
Derxia gummosa
Examples of Slime Production by Nitrogen2-fixing Bacteria
Beijerinckia sp.
Additional genera of free-living N2 fixers include
acid-tolerant microbes
e.g., Beijerinckia and Derxia
Two Genera of Acid-Tolerant, Nitrogen2-fixing Bacteria
Beijerinckia indica Derxia gummosa
Contain a large globules of poly-β-hydroxybutyrate at each end
15.10 Neisseria, Chromobacterium, and Relatives
Neisseria, Chromobacterium, and their relatives can
be isolated from animals, and some species of this
group are pathogenic
Characteristics of the Genera of Gram-Negative Cocci
Chromobacterium and Neisseria
Chromobacterium violaceum Violacein
Neisseria gonorrhoeae
15.11 Enteric Bacteria
Enteric Bacteria
Relatively homogeneous phylogenetic group within the
Gammaproteobacteria
Facultative aerobes
Motile or non-motile, nonsporulating rods
Possess relatively simple nutritional requirements
Ferment sugars to a variety of end products
Defining Characteristics of the Enteric Bacteria
Enteric bacteria can be separated into two broad
groups by the type and proportion of fermentation
products generated by anaerobic fermentation of
glucose
Mixed-acid fermentators
2,3-butanediol fermentators
Enteric Fermentations
Enteric Fermentations
Butanediol-Producing Bacterium
Erwinia carotovora
Diagnostic tests and differential media are often
used to identify various genera of enteric bacteria
Key Diagnostic Reactions Used to Separate Enteric Bacteria
Key Diagnostic Reactions Used to Separate Enteric Bacteria
A Simple Key to the Main Genera of Enteric Bacteria
Escherichia
Universal inhabitants of intestinal tract of humans and
warm-blooded animals
Synthesize vitamins for host
Some strains are pathogenic (O157:H7)
Salmonella and Shigella
Closely related to Escherichia
Usually pathogenic
Salmonella characterized immunologically by surface
antigens
Proteus
Genus containing rapidly motile cells; capable of
swarming
Frequent cause of urinary tract infections in humans
Swarming in Proteus
Proteus mirabilis with as bundle of peritrichous flagella
A swarming concentric colony of Proteus mirabilis
Butanediol fermentators are a closely related group
of organisms
Some capable of pigment production
Reactions Used to Separate 2,3-Butanediol Producers
Colonies of Serretia marcescens
Red-orange pigmentation of Serratia marcescens due to the pyrrole-containing “prodigiosin”