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Looking for syntrophic acetogen/methanogen interactions
Caroline Van Steendam
Final Report
Course Directors: Dr. Jared Leadbetter and dr. Dianne Newman
Microbial Diversity Course 2015
Caroline Van Steendam – Looking for syntrophic acetogen/methanogen interactions
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1 Introduction Many natural environments (e.g., soil sediments) and engineered systems (e.g., rice paddy soils and
wastewater treatment) are known to produce methane when anaerobically degrading organic matter.
Uncontrolled release of methane in natural environments should be minimized as methane is 23 times
more potent at retaining heat in the atmosphere than CO2. In contrast, methane production is often
maximized in engineered systems because of its high calorific value and therefore its suitability as an
(alternative) energy source. Even though the anaerobic degradation process of organic matter has been
studied in detail for decades, new discoveries are still made.
Fermenter acetogens and methanogens work together to convert intermediate degradation products, i.e.,
volatile fatty acids (VFAs), into methane. The fermentative conversion of VFAs is thermodynamically
unfavorable under standard conditions (1 M concentration, or 105 Pa for gases) and requires a continuous
removal of its reaction products by methanogens to overcome this energy barrier. On top of the well-
known syntrophic interactions including interspecies H2, formate, and acetate transfer, it has recently
been discovered that electrons can also be exchanged directly between the fermenter acetogen and
methanogen (direct interspecies electron transfer, DIET) (Chen et al., 2014; Liu et al., 2012; Nagarajan et
al., 2013; Shrestha et al., 2014; Shrestha et al., 2013; Summers et al., 2010; Zhao et al., 2015).
The goal of this miniproject is to isolate different types of methanogens from Cedar Swamp and to identify
what syntrophic interactions they are capable of. The first stage of the project consists of setting up
different culture enrichments with inoculum from Cedar Swamp, to select for (i) hydrogenotrophic
(utilizing H2 and CO2) and aceticlastic (utilizing acetate) methanogens, (ii) butyrate fermenting acetogens,
and (iii) co-cultures of such acetogens and methanogens. Two bench-scale microbial fuel cells (MFCs),
inoculated with a sample from Cedar Swamp, are set-up in parallel to select for acetogens and
methanogens that are capable of directly exchanging electrons. A potentiostat is used in the final stage of
the project to study the DIET capabilities of an enriched methanogenic culture.
2 Methods
2.1 Anaerobic Culturing A total of seven bottles were inoculated with Cedar Swamp samples, all of which containing the same basic
liquid media (see Appendix A) but varying in gaseous headspace and acetate, butyrate, and bicarb
concentrations (see Figure 1, liquid volume of 25 mL, gaseous volume of 132 mL). Table 1 shows the
reactions related to the different types of metabolism targeted in these bottles (Dong et al., 1994).
Table 1: Different reactions expected in cultures
Aceticlastic methanogenesis
𝐶𝐻3𝐶𝑂𝑂− + 𝐻2𝑂 ↔ 𝐻𝐶𝑂3− + 𝐶𝐻4 Reaction 1
Hydrogenotrophic methanogenesis
𝐶𝑂2 + 4𝐻2 ↔ 𝐶𝐻4 + 2𝐻2𝑂 Reaction 2
Butyrate fermentation (1)
𝐶4𝐻7𝑂2− + 2 𝐻𝐶𝑂3
− ↔ 2𝐶𝐻3𝐶𝑂𝑂− + 𝐻+ + 2 𝐻𝐶𝑂𝑂− Reaction 3
Butyrate fermentation (2)
𝐶4𝐻7𝑂2− + 2𝐻2𝑂 ↔ 2𝐶𝐻3𝐶𝑂𝑂− + 𝐻+ + 2 𝐻2 Reaction 4
Caroline Van Steendam – Looking for syntrophic acetogen/methanogen interactions
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The first bottle was given a 100% N2 headspace and was supplemented with 2 mM acetate, in order to
enrich for Methanosaeta, an aceticlastic methanogen (Reaction 1). The second bottle also had 100% N2 as
headspace but contained a higher acetate concentration for the more copiotrophic Methanosarcina, an
aceticlastic methanogen often dominating in systems with an acetate concentration above 4 mM (Conklin
et al., 2006). The third and fourth bottle had a headspace of 80% H2 and 20% CO2 to enrich for
hydrogenotrophic methanogens (Reaction 2), while only the third contained 1 mM bicarbonate (in case
some of the methanogens are heterotrophs and need an additional carbon source). A co-culture of a
butyrate degrader and an aceticlastic methanogen was enriched for in the 5th bottle by adding 2 mM
butyrate, 1 mM bicarb, and 0.01 mM acetate to the basic medium while supplying 100% N2 in the
headspace (optimal thermodynamic concentration of acetate, as shown in Figure 2, and the relevant
reactions are Reaction 1 and Reaction 3). The 6th bottle aimed at enriching a co-culture of a butyrate
degrader and a hydrogenotrophic methanogen, by only supplying 2 mM butyrate (Reaction 2 and Reaction
4). Glass slides were also added to bottles #5 and 6 to promote biofilm growth and give the acetogens and
methanogens the possibility to grow closer together. A butyrate fermenter was targeted in the last bottle,
by supplying 2 mM butyrate and a 100% N2 headspace.
Figure 1: Different cultures. 1,2: aceticlastic methanogens, 3, 4: hydrogenotrophic methanogens, 5: coculture of butyrate fermenter / aceticlastic methanogen, 6: coculture butyrate fermenter/hydrogenotrophic methanogen, 7: butyrate fermenter.
2.2 Microbial fuel cells Two MFCs were built using available lab equipment, by connection two glass jars (referred to as chambers
in the rest of the text) with a salt bridge for proton transfer and a copper wire for electron transfer (see
Figure 3). All four chambers were inoculated with Cedar Swamp sample and had a headspace of 100% N2,
however, different electron donors were supplied (total liquid volume of 50 mL). Both acetogenic
chambers were supplemented with 2 mM butyrate, while one methanogenic chamber just consisted of
Figure 2: Input (lefthand side) and output (righthand side) for thermodynamic excel sheet
Caroline Van Steendam – Looking for syntrophic acetogen/methanogen interactions
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the basic methanogenic medium and the other methanogenic chamber had an additional 0.01 mM of
acetate and 69 mM bicarb. Each chamber contained a submerged graphene rod attached to a wire with a
resistor (470 kΩ) in the middle, allowing for electron transport. The connection of both chambers via a salt
bridge, made by hardening a hot solution containing 2% agar and 1M KCl into a non-gas-permeable tube,
allowed for proton transport between both chambers. Finally, some sampling ports were added and the
chambers were connected to a N2-filled bottle to enhance the ability of the system to cope with pressure
increase.
Figure 3: Set-up of a microbial fuel cell
2.3 Potentiostat Another methanogenic chamber, containing the hyphomicrobium medium (see Appendix B) and a 100%
N2 headspace, was inoculated with a culture enriched in methylotrophic methanosarcina (see Figure 4).
Two graphene rods connected to the working and auxiliary electrode of a potentiostat were submerged
in the chamber, as well as a reference electrode. The potentiostat was set-up in such a manner that the
voltage through the working electrode equaled -0.5V vs standard hydrogen electrode. The chamber was,
just as with the microbial fuel cells, connected to a N2-filled bottle to prevent gas leakage by providing
more flexibility towards increased system pressure.
Figure 4: Set-up of chamber connected to the potentiostat
Caroline Van Steendam – Looking for syntrophic acetogen/methanogen interactions
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2.4 Chemical analyses The methane production in each bottle was quantified using a gas chromatograph (GC) connected to a
flame ionization detector. A gas-tight syringe was flushed with N2 before it was used to inject 250 µL of
sample into the GC. N2 was used as a carrier gas. A 12.7% methane standard was made by adding 20 ml
of CH4 to a N2-flushed vial of 157 ml, and 17 ml was added to a 69.56 ml vial to obtain a 24.44% standard
Both standards and a blank were run each time samples were analyzed, and all samples were run in
triplicates.
The acetate and butyrate concentrations were measured using a high pressure liquid chromatography
(HPLC) connected to a UV detector. Butyrate standards, ranging from 20, 10, 5, 2.5, to 1.25 mM, were run
once and used for the calibration of all samples. HPLC samples were prepared by centrifuging 900 µL of a
sample together with 100 µL of a 5N H2SO4 solution, and adding 550 µL of the supernatant to a HPLC vial.
2.5 Molecular analyses Two attempts at creating a clone library were made. In the first try the genomic DNA was obtained by
boiling the samples in ALP reagent (in order to take a sample from the liquid cultures, 750 µL of each
sample was centrifuged and the pellet was picked with a toothpick) after which PCR amplification was
performed with a mastermix solution (25 µL of GoTag green, 1 µL fwd primer, 1 µL rev primer 1341R, 20
µL NF H2O, 3 µL of the boiled template) and controlled with a gel extraction (1x TAE, 1% agarose LE, over
120 V). The PCR products were cloned into a plasmid vector (according to the pGEM T-easy cloning
procedure) and then transformed into E. coli (utilizing the transformation procedure) and plated onto LB
plates with ampicillin/IPTG/X-Gal.
The second attempt included using a DNA extraction kit (‘Wizard Genomic DNA Purification Kit’) instead
of performing boiling in an ALP solution. PCR amplification was performed with the same mastermix
solution, after which the PCR products were extracted with a gel.
2.6 Microscopy The available Zeiss microscope was used to visualize liquid mounts with a 100X objective while applying
phase contrast, while the measured excitation when transmitting Lucifer Yellow light was used to identify
methanogens.
The cultured samples were analyzed with CARD-FISH once, in order to identify and/or determine the
relative abundance of the present microorganisms. After fixing these planktonic cells on a filter using a 2%
PFA solution, the microorganisms were embedded with 0.1% agarose, and permeabilized using both a 1
mg/mL lysozyme solution and a fresh 15 µg/mL proteinase K solution. The endogenous peroxidases were
inactivated using a 0.01 M HCl solution (3% H2O2) and the samples were hybridized using a hybridization
buffer of the correct formamide concentration (e.g., probes ARCH 915 requires 35% formamide). The
filters were washed and the final CARD protocol was performed according to the manual (a detailed
rendition of these protocols can be found in Appendix C). The probes ARCH 915, NON338, EUB338 I-III,
MSMX860, and LGC354a were applied to stain Archaea, nothing (negative control), Bacteria,
Methanosarcinales, Firmicutes. The ZEIS microscope was used to visualize the fluorescence.
Mono-FISH was performed afterwards, where the fixed cells are directly hybridized after fixation using the
protocol shown in Appendix D. The ZEIS microscope was used to visualize the fluorescence.
Caroline Van Steendam – Looking for syntrophic acetogen/methanogen interactions
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3 Results and discussion
3.1 No methane production After setting up the seven cultures, the methane production and substrate removal was monitored using
GC and HPLC. Figure 5 shows the final GC results (the areas outputted by the program are converted to
moles using a standard calibration curves). Although distinct methane peaks can be seen on the GC, these
do not translate to large amounts of methane due to the steep slope of the standard calibration curves.
None of the cultures is, over the entire time period, capable of producing enough methane to surpass the
blank. As the maximum amount of methane that can be produced for, e.g., the 2 mM Acetate culture is
50 mmoles (>> the blank), the absence of methane in the chromatographs is not related to a too high
detection limit of the GC. Even though the outputted methane productions always fall below the employed
calibration curve (12.7 and 24.44% CH4), the expected amount is higher (as can be seen on the right hand
side of Figure 5). The low amounts of methane are thus also not caused by an extrapolation error.
As the low production of methane persisted, the somewhat turbid cultures (i.e., 1mM Ac, 2mM Ac, and
0mM Ac) were re-passaged on the 7th day of the experiment (now called P1 1mM Ac, P1 2mM Ac, and P1
0mM Ac respectively). These cultures showed a similar methane production trend. In a last attempt to
spike the methane production, each culture is re-inoculated with 2ml of the supernatant of Trunk River
sediment sample on the 14th day, again followed by no apparent increase in methane production.
Figure 5: (Left hand side) summary of GC data over entire culturing period, (right hand side) plot of the standard calibration values together with the actual and maximum methane production of the 2mM Acetate methanogenic culture on 8/16/2015
3.2 Variable trends in acetate concentrations and slight butyrate degradation The HPLC data of the methanogenic cultures, as shown in Figure 6.a, shows varying acetate concentration
trends. The 2mM Ac and 10 mM Ac bottles, for instance, show a small decrease in acetate concentration.
The decrease from 10 mM acetate to 8.145 mM acetate should have resulted in the production of 0.0464
moles of methane, which is about two orders of magnitude higher than the measured value (0.00025 mol).
It is not clear what the acetate was converted into, neither the HPLC nor the GC picked up increasing
concentrations of other organics. Based on the low increase in turbidity it can be excluded that the
organics were used for anabolic growth. The P1 1mM Ac and P1 2mM Ac bottles did not show any change
in acetate concentration, while an increase in acetate concentrations is observed in the 1mM Ac, 0mMAc,
and P1 0mM Ac bottles. These bottles were supplied with H2 and CO2 as a headspace, which are both
substrates for homoacetogens (4 𝐻2 + 2 𝐶𝑂2 ↔ 𝐶𝐻3𝐶𝑂𝑂𝐻 + 2 𝐻2𝑂). Even though homoacetogenesis is
0 2 4 6 8 10 12 14 160
1
2
3
4
5
6x 10
-4
Time [days]
Me
tha
ne
Pro
du
ctio
n [m
ol]
Methanogens
Blank
1mM Acetate
P1 1mM Acetate
2 mM Acetate
P1 2mM Acetate
10mM Acetate
0mM Acetate
P1 0mM Acetate
Acetogen
Coculture 0.01 mM Acetate
Coculture 0mM Acetate
10-7
10-6
10-5
10-4
105
106
107
108
109
1010
Amount of Methane [Mol]
Are
a [/]
Standard and Samples on day 16
Standard day 16
2 mMAc day 16
Maximum for 2mMAc
Caroline Van Steendam – Looking for syntrophic acetogen/methanogen interactions
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thermodynamically more unfavorable than hydrogenotrophic methanogesis, biological reasons can cause
the homoacetogens to dominate (e.g., faster growth). Re-inoculation of the bottles on the 14th day of the
experiment, caused the acetate trend to invert in the P1 0mM Ac bottle and resulted in a decreasing
acetate concentration. Since the experiment was stopped on the 16th day, however, this is just a
preliminary observation.
Figure 6.b shows that, even though the culture remained non-turbid throughout the experiment,
the butyrate concentration did decrease from 2 mM to 1.522 mM while the acetate concentration only
increased with 0.118 mM. The variable formate concentration, combined with the fact that this culture
never produced any gas, illustrates that butyrate was mostly degraded via Reaction 3. Given the low
thermodynamic favorability of butyrate degradation, it would have been better to replenish the medium
daily to keep the concentrations of the reaction products low and that of the reactants high. The addition
of Trunk River inoculum on the 14th day did not result in an extra decrease of butyrate concentration,
although a decreasing formate concentration is observed.
Figure 6.c and d show an initial decrease in butyrate concentration, and again this decrease is not
accompanied by a stoichiometrically correct increase in formate/acetate. The acetate and formate
concentrations, however, are seen to decrease after being accumulated for a couple of days, illustrating
that there are some formate and acetate consumers present that grow slower than the butyrate
degraders. To restore the butyrate concentration in the 0.01mM Ac co-culture and to decrease the amount
of acetate accumulated in the 0mM Ac co-culture, the medium is replenished on the 10th day of the
experiment. Both the replenishment of the medium and the addition of Trunk River inoculum on the 14th
day did not result in an extra decrease of butyrate concentration.
0 2 4 6 8 10 12 14 160
0.0625
0.125
0.1875
0.25
0.3125
0.375
0.4375
0.5
Time [days]
Ace
tate
/fo
rma
te c
on
ce
ntr
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n [m
M]
Coculture 0mM Acetate, 2mM Butyrate
0 2 4 6 8 10 12 14 160
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
Bu
tyra
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ntr
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M]
Acetate
Formate
Butyrate
0 2 4 6 8 10 12 14 160
0.0625
0.125
0.1875
0.25
0.3125
0.375
0.4375
0.5
Time [days]
Ace
tate
/fo
rma
te c
on
ce
ntr
atio
n [m
M]
Coculture 0.01mM Acetate, 2mM Butyrate
0 2 4 6 8 10 12 14 160
0.5
1
1.5
2
2.5
3
3.5
4
Bu
tyra
te c
on
ce
ntr
atio
n [m
M]
Acetate
Formate
Butyrate
0 2 4 6 8 10 12 14 160
0.125
0.25
0.375
0.5
0.625
0.75
0.875
1
Time [days]
Ace
tate
/fo
rma
te c
on
ce
ntr
atio
n [m
M]
Acetogen, 2mM Butyrate
0 2 4 6 8 10 12 14 160
0.5
1
1.5
2
2.5
3
3.5
4
Bu
tyra
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M]
Acetate
Formate
Butyrate
0 2 4 6 8 10 12 14 160
1
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7
8
9
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11
Time [days]
Ace
tate
co
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ntr
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M]
Methanogens
1mM Acetate
P1 1mM Acetate
2 mM Acetate
P1 2mM Acetate
10mM Acetate
0mM Acetate
P1 0mM Acetate
a. b.
c. d.
Figure 6: (a) Acetate concentrations in methanogenic cultures over entire culturing period, (b) Acetate and butyrate concentrations in acetogenic culture over entire culturing period, (c) Acetate and butyrate concentrations in co-culture supplemented with 0.01 mM Ac over entire culturing period, and (d) Acetate and butyrate concentrations in co-culture (no acetate) over entire culturing period
Caroline Van Steendam – Looking for syntrophic acetogen/methanogen interactions
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3.3 No direct electron transfer observed The microbial fuel cell did not produce any biogas nor was there any current/voltage measured along the
copper wires. Fu et al. (2015) noticed enhanced methane production as soon as a culture previously
enriched for DIET capabilities was entered in a potentiostat (-0.5V vs standard hydrogen electrode), with
a 6-fold increase over 160 hours. DIET in a coculture of G. metallireducens and G. sulfurreducens,
furthermore, was stimulated within two days upon addition of a conductive carbon cloth (Chen et al.,
2014). Although these results are promising, the examples started with microorganisms already capable
of DIET which can explain for the difficult start-up of the microbial fuel cells inoculated with a Cedar Swamp
sample. In order to facilitate DIET in the MFCs, it would have been desirable to re-inoculate the MFC-
chambers with a growing acetogenic and methanogenic culture.
A potentiostat consisting of a methanogenic chamber was employed to test the DIET capabilities of a
methanogenic culture. Several groups in the Microbial Diversity Course had been able to grow some
hydrogenotrophic methanogens, while one culture with a methylotrophic Methanosarcina was available.
As it is known that some Methanosarcina strains are capable of DIET (Rotaru et al., 2014), it would be
interesting to see if our specific strain was as well. The methylotrophic Methanosarcina was enriched in a
hyphomicrobium medium (a simple medium containing methanol and nitrate), and its identification was
solely based on microscopy images. Figure 7 shows autofluorescence with Lucifer Yellow fluorescence,
pointing towards the presence of methanogens (the autofluorescent cofactor F420 is a signature for
methanogens, (Solera et al., 2001)). The distinct tetrade structure of these methanogens, furthermore, is
typical for Methanosarcina species (Domingues et al., 2002). And finally, as the culture is growing on
methanol, it is known that there are methylotrophic Methanosarcina present.
In contrast to the set-up of the MFC, methanol was added as an electron donor to the potentiostat in order
to give the Methanosarcina some time to adjust its metabolisms towards favoring of DIET. After growing
for 5 days, no current was observed in the working electrode. It would have been desirable to measure
the methanol concentration over time in the system to see if at least the methanol was being utilized.
However, with the available GC and HPLC set-ups, this was impossible. The absence of current in the
working electrode could be caused by the slow adaptation of the present Methanosarcina species, or the
microorganisms might have been too comfortable with the readily available methanol in the medium.
Furthermore, it was not clear if an anaerobic atmosphere was maintained at all times.
A future revenue for isolating acetogens/methanogens capable of DIET in the future, might be to select
for microorganisms containing the required genetic material (e.g. cytochromes).
Figure 7: Autofluorescence with Lucifer Yellow fluorescence of (?) methylotrophic Methanosarcinas
Caroline Van Steendam – Looking for syntrophic acetogen/methanogen interactions
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3.4 Identification of microorganisms in cultures The same technique as described above with the methylotrophic Methanosarcina was successfully utilized
to detect the presence of methanogens in the cultures. In addition to normal microscopy, two attempts
were made to create a clone library of the cultures. Both attempts, of which the procedure is explained in
the Methods section, were unsuccessful. The first attempt resulted in no E. Coli growth, whereas the
second did not render any bands when checking the PCR products on a gel. Thirdly, one attempt at utilizing
CARD-FISH to identify and determine the relative abundance of Bacteria, Archaea, Methanosarcinales, and
Firmicutes failed. No fluorescence was discernible in the final result, which was probably due to failing of
the permeabilization step. This step often needs to be optimized for a specific sample, while there was not
enough time to do this at the end of the experiment. A final try at identification was performed with mono-
FISH, this time not with a Methanosarcinales probe as there was no mono-FISH probe available. The
resulting slides showed fluorescence for each of the probes (but not for the none probe), and provided
further confirmation of the presence of Archaea in the growing cultures (see Figure 8). There was not
enough time to study the amount of images necessary for a statistically correct relative abundance
quantification.
Figure 8: A dapi stained (left hand side) and Archaeal probe stained (right hand side) image of a sample of the 0.01 mM Ac co-culture.
Caroline Van Steendam – Looking for syntrophic acetogen/methanogen interactions
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4 Conclusion The goal of this miniproject was to isolate different types of methanogens from Cedar Swamp and to
identify what syntrophic interactions they are capable of. Isolation of methanogens proved to be difficult
(none of the ‘enriched’ cultures produced methane), although mono-FISH confirmed the presence of
Archaea in the bottles while microscopic analysis with Lucifer Yellow autofluorescence confirmed the
presence of methanogens. The addition of new inoculum from Trunk River did not result in enhanced
methanogenesis (over the course of two days). Homoacetogens were found in the bottles with a H2/CO2
headspace, as the acetate concentration was shown to increase over time. Acetate consumption was
observed in two bottles (fed with 2mM Ac and 10mM Ac), however, it was not clear what the carbon was
converted into. As these microorganisms degraded acetate, they would have been capable of
syntrophically interacting with a fermenter acetogen by exchanging acetate. The degradation of butyrate
and the production and consumption of acetate and formate in the bottles enriching for an
acetogenic/methanogenic co-culture illustrated the presence of a co-culture that syntrophically
transferred H2 and formate.
In contrast to acetate, H2, and formate interspecies transfer, no DIET was observed using the MFC and
potentiostat set-up. It is unclear, however, if this is due to biological reasons (e.g., more time might be
needed for the environmental sample to adapt its metabolism) or engineering problems (e.g., occasional
O2 leaks). It would have been informative to test the MFC/potentiostat set-up with a (co-) culture known
to exchange/accept electrons. Without proof of concept of the set-up itself, it is difficult to make
conclusions regarding the biology.
5 Acknowledgments Given the short amount of time for conceptualizing the idea for these experiments, building and
troubleshooting the set-ups employed, performing the actual experiments and the subsequent data
analysis, to finally writing and preparing a presentation and this report (three weeks), it is obvious that this
accomplishment involved the aid of many people. I want to thank Lina and Sebastian for their help with
anything anaerobic, which basically means for help with every step of this miniproject (e.g.,
MFC/potentiostat set-ups and GC/HPLC analysis). Thank you Kurt H., for your help with thinking about the
thermodynamics of my cultures. I owe Scott and Srijak gratitude for aiding with both attempts at creating
a clone library (and for their general kind-heartedness and ability to bring a smile to my face), and Emil for
his concise instructions regarding preparing and analyzing CARD and mono FISH samples. Thank you
Cristian for dealing with all the unhappy people and for allowing all lab-operations to go smoothly, as well
as Kristina and Rachel for their continuous help in making media/plates and finding random stuff. On a
different note, I am very thankful for Becky’s and Dave’s presence at the hospital after my unfortunate
collision with an impulsive 5 year old who definitely should be kept on a leash at all times. I want to thank
the construction engineers and architects of the LOEB building for providing us with such a great
conference room by day and epic movie theater by night (the FishBowl will never be forgotten).
A special call out to Dianne and Jared for creating such an enthusiastic and inspiring environment that
enabled us all to continuously push ourselves and to search for excellence in every aspect of our lives at
Woods Hole (although it seems fair to say that excellence was not reached, our quality of life in pursuit of
this goal was phenomenal). In conclusion, I want to thank all students, staff, and visitors for creating the
great atmosphere throughout the last 7 weeks that allowed us all to work hard while playing hard at the
same time.
Caroline Van Steendam – Looking for syntrophic acetogen/methanogen interactions
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6 References Chen, S., Rotaru, A.-E., Liu, F., Philips, J., Woodard, T.L., Nevin, K.P., and Lovley, D.R. (2014). Carbon cloth
stimulates direct interspecies electron transfer in syntrophic co-cultures. Bioresource Technology, 173(0), 82-86. doi: http://dx.doi.org/10.1016/j.biortech.2014.09.009
Conklin, A., Stensel, H.D., and Ferguson, J. (2006). Growth Kinetics and Competition between Methanosarcina and Methanosaeta in Mesophilic Anaerobic Digestion. Water Environment Research, 78(5), 486-496. doi: 10.2307/25053536
Domingues, M.R., Araujo, J.C., Varesche, M.B.A., and Vazoller, R.F. (2002). Evaluation of thermophilic anaerobic microbial consortia using fluorescence in situ hybridization (FISH). Water Science and Technology, 45(10), 27-33.
Dong, X., Cheng, G., and Stams, A.J.M. (1994). Butyrate oxidation by Syntrophospora bryantii in co-culture with different methanogens and in pure culture with pentenoate as electron acceptor. Applied Microbiology and Biotechnology, 42(4), 647-652. doi: 10.1007/BF00173934
Fu, Q., Kuramochi, Y., Fukushima, N., Maeda, H., Sato, K., and Kobayashi, H. (2015). Bioelectrochemical Analyses of the Development of a Thermophilic Biocathode Catalyzing Electromethanogenesis. Environmental Science & Technology, 49(2), 1225-1232. doi: 10.1021/es5052233
Liu, F., Rotaru, A.-E., Shrestha, P.M., Malvankar, N.S., Nevin, K.P., and Lovley, D.R. (2012). Promoting direct interspecies electron transfer with activated carbon. Energy and Environmental Science, 5, 8982-8989.
Nagarajan, H., Embree, M., Rotaru, A.-E., Shrestha, P.M., Feist, A.M., Palsson, B.Ø., Lovley, D.R., and Zengler, K. (2013). Characterization and modelling of interspecies electron transfer mechanisms and microbial community dynamics of a syntrophic association. Nat Commun, 4. doi: 10.1038/ncomms3809
Rotaru, A.-E., Shrestha, P.M., Liu, F., Shrestha, M., Shrestha, D., Embree, M., Zengler, K., Wardman, C., Nevin, K.P., and Lovley, D.R. (2014). A new model for electron flow during anaerobic digestion - DIET to Methanosaeta for the reduction of carbon dioxide to methane. Energy and Environmental Science, 7, 408-415.
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Appendix A – Media preparation (2015 Microbial Diversity Course
Manual) Use fresh-water mineral media, with, for 1 liter:
100X FW-Base 10 ml
1 M NH4Cl solution 5 ml
100 mM K phos, pH 7.2 10 ml
1 M MOPS buffer, pH 7.2 5 ml
Trace elements 1 ml
1% Resazurin 100 µl
Boil this mixture for 10 minutes in 3 L flasks under N2/CO2 (80/20 v%). Cool under stream of N2/CO2 gas
Multivitamin solution 1 ml
Sodium bicarbonate, 1 M 69 ml
Medium should become pink. Stopper round the bottom flask and bring into the anaerobic chamber. Add 1 mL per liter of 1 M sodium sulfide and stopper the flask. Wait for the color to become clear. Dispense 25 ml each each to all bottles and stopper. Crimp the bottles outside the anaerobic chamber and autoclave such that the bottles have an autoclave bin covering the top to minimize harm caused in case of an explosion. Once out of the autoclave, wait to remove the top auctoclave bin till they are cool to touch. Slight precipitation might occur post-autoclaving. This will disappear once the medium is cool. Store in dark.
Make 100X FW-base (for 100 X stock)
Component Amount MW (g/mol) 100X conc (stock) Final conc (1X)
NaCl 100 g 58.44 1711 mM 17.1 mM
MgCl2.6H2O 40 g 203.30 197 mM 1.97 mM
CaCl2.2H2O 10 g 147.02 68 mM 0.68 mM
KCl 50 g 74.56 671 mM 6.71 mM
Make 100X/100 mM K phoshate, pH 7.2 (for 100 X stock)
Component Amount MW (g/mol) 100X conc (stock) Final conc (1X)
KH2PO4/K2HPO4 4.0/12.7 g 136.1/714.2 100 mM 1 mM
Make MOPS buffer (per liter)
Component Amount MW (g/mol) 100X conc (stock) Final conc (1X)
MOPS free acid 209.26 g 209.26 1000 mM 5-20 mM
5M NaOH 100 ml 500 mM
Dissolve MOPS in 750 ml H2O, add 100 ml NaOH. The pKa of MOPS is 7.2, so 0.5 M NaOH should put it spot on pH 7.2, but do confirm and adjust the pH to 7.2 with dilute HCl or dilute NaOH as needed, and then adjust volume to 1000 ml.
Note that some aerobic organisms can use MOPS as C and/or S source, this is rare, but in rate cases ‘negative controls’ that are otherwise C and N free will yield growth
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Filter sterilize concentrated stock and keep out of light
Add to base media before autoclaving unless otherwise stated
Make 1000X HCl-Dissolved trace elements stock solution (per liter)
Component Amount MW (g/mol) 100X conc (stock) Final conc (1X)
20 mM HCl 1.7 ml conc HCl Na 20 mM 20 µM
FeSO4.7H2O 2100 mg 278.01 197 mM 1.97 mM
H3BO3 30 mg 61.83 0.48 mM 0.48 µM
MnCl2.6H2O 100 mg 197.91 0.5 mM 0.5 µM
CoCl2.6H2O 190 mg 237.93 6.8 mM 6.8 µM
NiCl2.6H2O 24 mg 237.69 1.0 mM 1.0 µM
CuCl2.2H2O 2 mg 170.48 12 µM 12 nM
ZnSO4.7H2O 144 mg 287.56 0.5 mM 0.5 µM
Na2MoO4.2H2O 36 mg 241.95 0.15 mM 0.15 µM
NaVO3 3 mg 121.93 25 µM 25 nM
Na2WO4.2H2O 3 mg 329.85 9 µM 9 nM
Na2SeO3.5H2O 6 mg 263.01 23 µM 23 nM
Make multivitamin solution
Component Amount 1000X conc. Final conc.
10 mM MOPS, pH 7.2 1000 ml 10 mM 10 µM
Riboflavin 100 mg 0.1 mg/ml 0.1 µg/ml
Biotin 30 mg 0.03 mg/ml 0.03 µg/ml
Thiamine HCl 100 mg 0.1 mg/ml 0.1 µg/ml
L-Ascorbic acid 100 mg 0.1 mg/ml 0.1 µg/ml
d-Ca-pantothenate 100 mg 0.1 mg/ml 0.1 µg/ml
Folic acid 100 mg 0.1 mg/ml 0.1 µg/ml
Nicotinic acid 100 mg 0.1 mg/ml 0.1 µg/ml
4-aminobenzoic acid 100 mg 0.1 mg/ml 0.1 µg/ml
Pyridoxine HCl 100 mg 0.1 mg/ml 0.1 µg/ml
Lipoic acid 100 mg 0.1 mg/ml 0.1 µg/ml
NAD 100 mg 0.1 mg/ml 0.1 µg/ml
Thiamine pyrophosphate
100 mg 0.1 mg/ml 0.1 µg/ml
Cyanocobalamin 10 mg 0.01 mg/ml 0.01 µg/ml
Titrate with 5 M NaOH (5-10 drops) until dissolved.
Filter sterilize (0.2 µm filter) and regriferate in the dark in 10 ml aliquote
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Appendix B: Hyphomicrobium medium (2015 Microbial Diversity Course
Manual)
Appendix C: CARD-FISH protocols (2015 Microbial Diversity Course
Manual) Fixation of planktonic samples
Embedding
Permeabilization
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Inactivation of endogenous peroxidases
Hybridization
Washing
CARD
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Appendix D: Mono-FISH protocols (2015 Microbial Diversity Course
Manual) Hybridization
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