bs_bs_banner
Environmental Microbiology Reports (2014) 6(1), 100–105
doi:10.1111/1758-2229.12113
Anaerobic ammonium oxidation with an anode as the
electron acceptor
Bo Qu, Bin Fan,* Shikun Zhu and Yali Zheng
State Key Laboratory of Environmental Aquatic
Chemistry, Research Center for Eco-Environmental
Sciences, Chinese Academy of Sciences, Beijing
100085, China.
Summary
Anaerobic ammonium oxidation with an anode as the
electron acceptor was realized in a dual-chamber
microbial electrolysis cell (MEC). Nitrate was the main
product that accounted for approximately 95% of
ammonium consumed, but nitrite was also detectable. Using 16S ribosomal RNA analysis, we found
that the microbial community attached to the electrode was dominated by Nitrosomonas europaea
(40.3%) and the genus Empedobacter (34.7%), but no
anammox bacteria were detected. Nitrosomonas
europaea was shown to be necessary with an inhibition assay using allylthiourea. Certain soluble
metabolites were found to have an important
effect on the current production. These results show
that there are many ways to oxidize ammonium
biologically.
Introduction
The oxidation of ammonium is a critical step of the biological nitrogen cycle in natural environment, as well as
in various artificial processes for eliminating nitrogen pollutants. There are two accepted pathway responsible for
biological ammonium oxidation. In general, ammonium is
sequentially oxidized to nitrate (NO3−) with molecular
oxygen (O2) as the electron acceptor by specific groups
of bacteria (Kowalchuk and Stephen, 2001) and archaea
(Konneke et al., 2005). In the absence of O2, ammonium
also can be oxidized with nitrite (NO2−) or NO3− as the
electron acceptor to produce dinitrogen (N2) in a process
called anammox (Kuenen, 2008), which catalysed by a
group of bacteria known as anammox bacteria that
belong to the phylum plancomycetes (Strous et al.,
Received 17 February, 2013; revised 13 September, 2013; accepted
26 September, 2013. *For correspondence. E-mail fanbin@
rcees.ac.cn; Tel. (+86) (0)10 62849142; Fax (+86) (0)10 62849142.
© 2013 Society for Applied Microbiology and John Wiley & Sons Ltd
1999; Kartal et al., 2011). However, several
biogeochemical studies have indicated that there may
be more pathways for biological ammonium oxidation.
Clement and colleagues (2005) and Shrestha and
colleagues (2009) reported respectively that ammonium
oxidation was coupled to dissimilatory reduction of iron
to produce NO2− under anaerobic conditions in wetland
soils. More recently, Yang and colleagues (2012) found
that anammox might be coupled to iron reduction. In this
process, N2, NO2− and NO3− were produced in anaerobic
tropical upland soils, and N2 was the dominant product.
The evidence in these studies suggested that some
microorganisms may use Fe (III) as a terminal electron
acceptor for anaerobic ammonium oxidation. Fe (III) primarily exists as insoluble, solid-phase minerals in
circumneutral pH environment (Weber, 2006). Therefore,
the extracellular electron transfer would be a potential
mechanism involved in anaerobic ammonium oxidation
coupled to solid-phase electron acceptors, suggesting
that this reaction may also proceed in bioelectrochemical systems (BESs), in which electrodes
could serve as the terminal electron acceptor.
Extracellular electron transfer results from a need of
respiration (Gralnick and Newman, 2007; Lovley, 2008).
Many microorganisms have evolved mechanisms to
move electrons outside of the cellular membrane to
respire solid surfaces by using bacterial nanowires, outermembrane metalloproteins and/or soluble electron shuttles (Rabaey et al., 2007; Marsili et al., 2008; Logan,
2009). The most BESs reported by far were operated with
organic compounds as substrates (Pant et al., 2010).
Although some researchers speculated that ammonium
could also be used as substrate in BESs due to this
process capable of supplying electrons and energy (Kim
et al., 2008; He et al., 2009), it is not yet well demonstrated experimentally, and little is known about the
mechanisms responsible for this process.
In this study, the possibility of anaerobic ammonium
oxidation with an electrode as the electron acceptor was
investigated by using a dual-chamber MEC with freshwater sediments as original inoculum, and with ammonium as the sole electron donor. The reaction products
and the current were monitored, and the microbial community structure of the enrichment culture on the electrode surface was assessed through 16S ribosomal RNA
(rRNA) gene analysis.
Anaerobic ammonium oxidation with electrode reduction
Fig. 1. Electrical current production with ammonium as electron
donor in a microbial electrolysis cell inoculated with freshwater
sediments.
A. Electrical current production from ammonium (5 mM) after
sediments were inoculated into the anode chamber.
B. Electrical current production from repeated addition of
ammonium (5 mM) with and without medium replacement. Arrows
indicate points at which ammonia was added with and without
medium replacement.
101
inoculum, the growth medium in the anode chamber was
replaced for several times to wash out all the residues of
the inoculum. All manipulations were done under the strict
anaerobic conditions. When ammonium was added
again, current production resumed after a brief lag. The
third addition of ammonium resulted in a higher rate of
current production without any lag and then generated a
peak current of 0.698 mA (Fig. 1B), but subsequent additions typically did not increase current output significantly.
Addition of more ammonium (e.g. 10 mM) also could not
enhance the rate and peak value of current production,
but proportionally prolonged the duration of current production (data not shown).
A representative result of the current production and the
concentrations of ammonium, NO3− and NO2− in the anode
chamber after each addition of ammonium was shown in
Fig. 2. Along with electrical current production, ammonium was consumed with NO3− as the main product. NO2−
was also detected, but its concentration was always
below the level of 0.1 mM. When ammonium was
depleted, the current declined to the background level
(< 0.01 mA), and the cumulative NO3− accounted for
95.4 ± 2.7% (mean ± standard deviation; n = 6) of the
ammonium consumption.
In contrast, there was no loss of ammonium and no
current more than the background level was observed in
the control MEC in which no sediment was inoculated.
Moreover, ammonium consumption as well as NO3− and
NO2− production would not be detected if the anode was
disconnected from the cathode (data not shown). These
results indicated that the ammonium oxidation was mainly
an anaerobic biological process, in which the anode
served as the terminal electron acceptor.
Results and discussion
Electrical currents and reaction products
Experiments were conducted using microbial electrolysis
cells (MECs), with anode and cathode chambers separated by a proton exchange membrane. Polished graphite
plates were used for both anode and cathode. Strict
anaerobic condition was maintained in both chambers by
flushing with high purity helium gas throughout the experiments (details described in supporting information).
Freshwater sediments (20 ml) were inoculated into the
anode chamber (180 ml), and then ammonium sulphate
(5 mM NH4+) was provided as the sole electron donor. In
the start-up period, the currents increased gradually after
a lag of 3–5 days, and then rapidly rose to a peak current
at the 8th day, followed a rapid decline (Fig. 1A) due to the
exhaustion of ammonium (verified by analysis of ammonium). To determine if the current production was facilitated by planktonic cells or by organic components in the
Fig. 2. A representative result of the current, nitrate and nitrite
concentrations in the anode chamber after the addition of 5 mM
ammonium. Inset gives data of nitrite concentration. Arrows indicate
point at which ammonium was added.
© 2013 Society for Applied Microbiology and John Wiley & Sons Ltd, Environmental Microbiology Reports, 6, 100–105
102 B. Qu et al.
Fig. 3. Effect of medium replacement on current production. The
current by a mature culture that produced the stable current for 7
days without medium replacement (closed symbols and black
trace), decline after replacement of fresh medium containing 5 mM
ammonium (open symbols and red trace) and recovery after
replacement of the mature medium (closed symbols and black
trace).
The coulombic efficiency (CE) was calculated to
address the recovery of electron as electrical current from
the oxidation of ammonium to NO3−. In mature cultures,
the CE calculated for a single addition of ammonium was
32.7 ± 7.7% (n = 6). This value is generally lower than
those reported by other MECs studies using acetate as
substrate (Chae et al., 2009; Geelhoed and Stams, 2011).
However, the reported CEs in MEC varied widely, with
values ranging from 23% to 96% (Liu et al., 2010). For an
MEC, the potential causes for a low CE are the loss of
substrate due to methanogenesis (Call and Logan, 2008)
and/or producing other electron sinks, such as secondary
metabolites (Torres et al., 2010) and soluble microbial
products (SMP) (Laspidou and Rittmann, 2002;
Parameswaran et al., 2009). In this study, the possibility of
methanogenesis occurring at the anode can be excluded
because ammonium as substrate cannot support the
growth of methanogens. Thus, the most possible reasons
for the reduced CE would be that the majority of electrons
from ammonium oxidation diverted from electrical current
but into SMP and secondary metabolites. As described
below, the possibilities were supported by the present of
soluble metabolites in the mature culture, and a pronounced enrichment of heterotrophic bacteria accompanied by autotrophic nitrifying bacteria, which suggests
that the SMP was produced by nitrifiers to support
heterotrophic growth.
Effects of soluble metabolites
The colorless medium in the anode chamber gradually
becoming light yellow after several days of running (typically 5–7 days) without the replacement of medium (shown
in supporting information, Fig. S1). In contrast, no color
change was observed in the anode chamber of the control
MEC operated over 2 months. Moreover, we found that
medium replacement caused a slower current increase
(shown in supporting information, Fig. S2). This observation suggested that some microbial metabolites were
involved in electron transfer to the electrode because it had
been shown that medium replacement had no significant
impact on current production if electrode-attached cells
use direct contact as an only mechanism for transfer
electron to the electrode (Bond and Lovley, 2003).
To further investigate whether the potential microbial
metabolites involved in electron transfer, medium replacement was performed with the mature culture that produced a stable current for 7 days without medium
replacement (Fig. 3). Fresh medium caused a sharp
decline in current production from approximately 0.69 mA
to 0.08 mA, but when the mature medium was filtered with
0.22 μm-pore-diameter membrane and then returned into
the anode chamber, current production was immediately
restored to 85% of its original level within 1.5 h. In contrast, if the mature medium was not returned to replace
the fresh medium, the current recovered back to similar
level over 26 h. Repeated rounds of medium replacement
produced similar results (data not shown). Medium
replacement would remove the potential microbial
metabolites as electron shuttle released to the medium
and was frequently used as a method to determine
whether electron shuttle is involved in extracellular electron transfer (Gregory et al., 2004; Marsili et al., 2008).
These results indicated the present of soluble metabolites
in mature medium able to promote electron transfer to the
electrode.
With the present results, it is not possible to determine
whether the color change of medium with current production was the direct result of the production of the soluble
metabolites. Attempts are underway to develop methods
to identify the soluble metabolites and further elucidate its
origin and role in electron transfer to electrodes. Additionally, we cannot exclude the possibility that electrodeattached cells might be able to transfer electrons to the
electrode via direct contact in the absent of electron shuttles. However, the results present clearly indicated the
importance of soluble metabolites involved in electron
transfer to the electrode.
Analysis of the microbial community attached to
the electrode
After the reactor was operated for 2 months, the anode
was removed and the attached biomass was extracted.
The composition of 16S rRNA gene sequences on the
surface of anode was compared with the original
inoculum (Fig. 4). There was a pronounced enrichment of
© 2013 Society for Applied Microbiology and John Wiley & Sons Ltd, Environmental Microbiology Reports, 6, 100–105
Anaerobic ammonium oxidation with electrode reduction
50
Persentage 16S rRNA clones (%)
Sediment
Anode biofilm
40
30
20
10
0
Proteobacteria
Fig. 4. Relative proportions of 16S rRNA gene sequences from
clone libraries of the original inoculum and microbial community
attached on the anodic electrode. Percentages are based on 451
and 375 sequences from clone libraries of the original inoculum
and attached microbial community respectively. The right side of
dashed line indicates relative proportions of sequences most similar
to N. europaea and the genus Empedobacter from clone libraries of
the original inoculum and microbial community attached on the
anodic electrode.
microorganisms belonging to the β-Proteobacteria and
Bacteroidetes, which represented 41.6% and 36.0% of
the total bacteria population respectively. No other microorganisms accounted for more than 8% of the total bacteria population colonizing the electrode. Furthermore,
96.8% of the sequences in β-Proteobacteria were most
similar to Nitrosomonas europaea, and 96.3% of the
sequences in Bacteroidetes were most similar to the
genus Empedobacter (Fig. 4; supporting information,
Table S1). The microorganisms known capable of
extracellular electron transfer, such as some members in
Geobacteraceae, were not found in community attached
to the electrode, although they were present in the original
inoculum and accounted for 2.2% of the total bacteria
population (data not shown). No anammox bacteria were
detected in community on the electrode using qualitative
polymerase chain reaction assays.
It was interesting to find that N. europaea and the genus
Empedobacter were highly enriched and dominated
the microbial community on the anode. Nitrosomonas
europaea is the most commonly investigated nitrifying
bacteria being able to oxidize ammonium to NO2−, with
molecular O2 as the electron acceptor (Bock and Wagner,
2006). Up till now, N. europaea has not been reported to
possess extracellular electron transfer ability. However, the
fact that N. europaea is able to anaerobically oxidize
103
ammonium with NO2− as an electron acceptor (Bock et al.,
1995; Beaumont et al., 2002) suggests that molecular O2 is
not indispensable for its respiration. To further investigate
whether N. europaea was directly related to the ammonium consumption and current production, allylthiourea
(ATU), a specific inhibitor of N. europaea (Juliette et al.,
1993), was added into the anode chamber. The addition of
0.1 mM of ATU caused an immediate decline of the current
production and ammonium consumption (shown in supporting information, Fig. S3), indicating that N. europaea
are indeed indispensable for the anaerobic ammonium
oxidation with anode as electron acceptor.
The genus Empodebacter is a group of chemoheterotrophic bacteria, which is capable of actively secreting the
unidentified yellow pigments (Jooste and Hugo, 1999). It
is known that a phylogenetically and metabolically diverse
heterotrophic community would be supported by
autotrophic growth of nitrifiers via production of SMP
(Furumai and Rittmann, 1992; Kindaichi et al., 2004).
However, 16S rRNA gene sequences analysis demonstrated that only the genus Empedobacter rather than
other heterotrophic bacteria were highly enriched on the
anode. A possible explanation for the specific enrichment
of the genus Empedobacter may be that they were
directly involved in electron transfer to electrode for
anaerobic ammonium oxidation, which in return provided
themselves with a competitive advantage over other
heterotrophs. Previous studies have demonstrated that
Pseudomonas sp. produced metabolites as electron shuttles, which enable other bacteria to achieve extracellular
electron transfer (Rabaey et al., 2005; Pham et al., 2008).
It is possible that the genus Empedobacter use a similar
strategy to enable N. europaea to achieve extracellular
electron transfer for anaerobic ammonium oxidation with
the electrode as the electron acceptor, especially considering that the important effects of certain soluble metabolites on the current production. Clearly, the present
concept is still largely hypothetical, and further research
on the interactions between N. europaea and the genus
Empedobacter and the electrode are necessary.
Nitrate as a main product of the anaerobic ammonium
oxidation with anode as electron acceptor is not an
expected result. It is known that N. europaea cannot
oxidize ammonium to NO3− because of lacking of nitrite
oxidoreductase. However, analysis of 16S rRNA genes
showed that no sequence recovered from the electrode
was closely related to the sequences of known nitriteoxidizing bacteria (shown in supporting information,
Table S1). A study by He and colleagues (2009) reported
that NO3− accounted for 14.4 ± 19.9% of ammonium
consumption in an ammonium-fed MFC. In that study,
nitrite-oxidizing bacteria also could not be found on either
the anode or the cathode. NO2− detected in the low concentration strongly suggested that it was an intermediate of
© 2013 Society for Applied Microbiology and John Wiley & Sons Ltd, Environmental Microbiology Reports, 6, 100–105
104 B. Qu et al.
anaerobic ammonium oxidation. Thus, further studies are
needed to determine the pathway responsible for oxidizing
NO2− to NO3−.
Conclusively, the results presented here demonstrate
for the first time that ammonium can be anaerobically
oxidized to NO3− with an electrode as the terminal electron
acceptor in a MEC. The finding may provide novel insight
into the pathways of biological ammonium oxidation and
have potential application in developing new methods for
eliminating ammonium pollution. To further elucidate the
mechanisms for this process, however, a better understanding of why and how N. europaea and the genus
Empedobacter work together, and the whole process of
the extracellular electron transfer need to be focused on in
future studies.
Acknowledgements
We thank Dr. Guibing Zhu for valuable discussions and comments on the original manuscript, and for help with molecular
experiments. This research is financially supported by the
National Natural Science Foundation of China (No. 51278484
and No. 51308528) and the Major Science and Technology
Program for Water Pollution Control and Treatment of China
(No. 2011ZX07301-003).
References
Beaumont, H.J., Hommes, N.G., Sayavedra-Soto, L.A., Arp,
D.J., Arciero, D.M., Hooper, A.B., et al. (2002) Nitrite
reductase of Nitrosomonas europaea is not essential for
production of gaseous nitrogen oxides and confers tolerance to nitrite. J Bacteriol 184: 2557–2560.
Bock, E., and Wagner, M. (2006) Oxidation of inorganic
nitrogen compounds as an energy source. Prokaryotes 2:
457–495.
Bock, E., Schmidt, I., Striven, R., and Zart, D. (1995) Nitrogen
loss caused by denitrifying Nitrosomonas cells using
ammonium or hydrogen as electron donors and nitrite as
electron acceptor. Arch Microbiol 163: 16–20.
Bond, D.R., and Lovley, D.R. (2003) Electricity production by
Geobacter sulfurreducens attached to electrodes. Appl
Environ Microbiol 69: 1548–1555.
Call, D., and Logan, B.E. (2008) Hydrogen production in a
single chamber microbial electrolysis cell lacking a membrane. Environ Sci Technol 42: 3401–3406.
Chae, K.J., Choi, M.J., Kim, K.Y., Ajaye, F.F., Chang, I.S., and
Kim, A.I.S. (2009) A solar-powered microbial electrolysis
cell with a platinum catalyst-free cathode to produce hydrogen. Environ Sci Technol 43: 9525–9530.
Clement, J.C., Shrestha, J., Ehrenfeld, J.G., and Jaffe, P.R.
(2005) Ammonium oxidation coupled to dissimilatory
reduction of iron under anaerobic conditions in wetland
soils. Soil Biol Biochem 37: 2323–2328.
Furumai, H., and Rittmann, B.E. (1992) Advanced modeling
of mixed populations of heterotrophs and nitrifiers
considering the formation and exchange of soluble microbial products. Water Sci Technol 26: 493–502.
Geelhoed, J.S., and Stams, A.J.M. (2011) Electricity-assisted
biological hydrogen production from acetate by Geobacter
sulfurreducens. Environ Sci Technol 45: 815–820.
Gralnick, J.A., and Newman, D.K. (2007) Extracellular respiration. Mol Microbiol 65: 1–11.
Gregory, K.B., Bond, D.R., and Lovley, D.R. (2004) Graphite
electrodes as electron donors for anaerobic respiration.
Environ Microbiol 6: 596–604.
He, Z., Kan, J., Wang, Y., Huang, Y., Mansfeld, F., and
Nealson, K.H. (2009) Electricity production coupled to
ammonium in a microbial fuel cell. Environ Sci Technol 43:
3391–3397.
Jooste, P.J., and Hugo, C.J. (1999) The taxonomy, ecology
and cultivation of bacterial genera belonging to the family
Flavobacteriaceae. Int J Food Microbiol 53: 81–94.
Juliette, L.Y., Hyman, M.R., and Arp, D.J. (1993) Inhibition of
ammonia oxidation in Nitrosomonas europaea by sulfur
compounds: thioethers are oxidized to sulfoxides by
ammonia monooxygenase. Appl Environ Microbiol 59:
3718–3727.
Kartal, B., Maalcke, W.J., de Almeida, N.M., Cirpus, I.,
Gloerich, J., Geerts, W., et al. (2011) Molecular mechanism
of anaerobic ammonium oxidation. Nature 479: 127–130.
Kim, J.R., Zuo, Y., Regan, J.M., and Logan, B.E. (2008)
Analysis of ammonia loss mechanisms in microbial fuel
cells treating animal wastewater. Biotechnol Bioeng 99:
1120–1127.
Kindaichi, T., Ito, T., and Okabe, S. (2004) Ecophysiological
interaction between nitrifying bacteria and heterotrophic
bacteria in autotrophic nitrifying biofilms as determined by
microautoradiography-fluorescence in situ hybridization.
Appl Environ Microbiol 70: 1641–1650.
Konneke, M., Bernhard, A.E., de la Torre, J.R., Walker, C.B.,
Waterbury, J.B., and Stahl, D.A. (2005) Isolation of an
autotrophic ammonia-oxidizing marine archaeon. Nature
437: 543–546.
Kowalchuk, G.A., and Stephen, J.R. (2001) Ammoniaoxidizing bacteria: a model for molecular microbial ecology.
Annu Rev Microbiol 55: 485–529.
Kuenen, J.G. (2008) Anammox bacteria: from discovery to
application. Nature Rev Microbial 6: 320–326.
Laspidou, C.S., and Rittmann, B.E. (2002) A unified theory for
extracellular polymeric substances, soluble microbial
products, and active and inert biomass. Water Res 36:
2711–2720.
Liu, H., Hu, H., Chignell, J., and Fan, Y. (2010) Microbial
electrolysis: novel technology for hydrogen production from
biomass. Biofuels 1: 129–142.
Logan, B.E. (2009) Exoelectrogenic bacteria that power
microbial fuel cells. Nat Rev Microbiol 7: 375–381.
Lovley, D.R. (2008) Extracellular electron transfer: wires,
capacitors, iron lungs, and more. Geobiology 6: 225–231.
Marsili, E., Baron, D.B., Shikhare, I.D., Coursolle, D.,
Gralnick, J.A., and Bond, D.R. (2008) Shewanella secretes
flavins that mediate extracellular electron transfer. Proc
Natl Acad Sci U S A 105: 3968–3973.
Pant, D., Van Bogaert, G., Diels, L., and Vanbroekhoven, K.
(2010) A review of the substrates used in microbial fuel
© 2013 Society for Applied Microbiology and John Wiley & Sons Ltd, Environmental Microbiology Reports, 6, 100–105
Anaerobic ammonium oxidation with electrode reduction
cells (MFCs) for sustainable energy production. Bioresour
Technol 101: 1533–1543.
Parameswaran, P., Torres, C.T., Lee, H., Krajmalnik-Brown,
B., and Rittmann, B.E. (2009) Syntrophic interactions
among anode respiring bacteria (ARB) and non-ARB in a
biofilm anode. Biotechnol Bioeng 103: 513–523.
Pham, T.H., Boon, N., Aelterman, P., Clauwaert, P.,
De Schamphelaire, L., Vanhaecke, L., et al. (2008)
Metabolites produced by Pseudomonas sp. enable a
Grampositive bacterium to achieve extracellular electron
transfer. Appl Microbiol Biotechnol 77: 1119–1129.
Rabaey, K., Boon, N., Hofte, M., and Verstraete, W. (2005)
Microbial phenazine production enhances electron transfer
in biofuel cells. Environ Sci Technol 39: 3401–3408.
Rabaey, K., Rodriguez, J., Blackall, L.L., Keller, J., Gross, P.,
Batstone, D., et al. (2007) Microbial ecology meets electrochemistry: electricity-driven and driving communities.
ISME J 1: 9–18.
Shrestha, J., Rich, J., Ehrenfeld, J., and Jaffe, P. (2009)
Oxidation of ammonium to nitrite under iron-reducing
conditions in wetland soils: laboratory, field demonstrations, and push-pull rate determination. Soil Sci 174: 156–
164.
Strous, M., Fuerst, J.A., Kramer, E.H.M., Logemann, S.,
Muyzer, G., van de Pas-Schoonen, K., et al. (1999)
Missing lithotroph identified as new planctomycete. Nature
400: 446–449.
Torres, C.I., Marcus, A.K., Lee, H.S., Parameswaran, P.,
Krajmalnik-Brown, R., and Rittmann, B.E. (2010) A kinetic
105
perspective on extracellular electron transfer by anoderespiring bacteria. FEMS Microbiol Rev 34: 3–17.
Weber, K.A. (2006) Microbes pumping iron: anaerobic microbial iron oxidation and reduction. Nat Rev Microbiol 4:
752–764.
Yang, W.H., Weber, K.A., and Silver, W.H. (2012) Nitrogen
loss from soil through anaerobic ammonium oxidation
coupled to iron reduction. Nat Geosci 5: 538–541.
Supporting information
Additional Supporting Information may be found in the online
version of this article at the publisher’s web-site:
Fig. S1. Color change of the medium in the anode chamber
as current production.
A. Medium from the anodic chamber of the MEC operated for
7 days without medium replacement.
B. Fresh medium.
Fig. S2. Effect of medium replacement on current production.
Arrows indicate point at which ammonium was added.
Fig. S3. Effect of the addition of allylthiourea (ATU) on current
production and ammonium consumption. Arrow indicates the
point at which 0.1 mM of ATU was added.
Table S1. Phylogenetic affiliation of clone sequences of bacterial 16S rRNA genes recovered from the microbial community attached to the anodic electrode.
Appendix S1. Experimental procedures.
Appendix S2. References.
© 2013 Society for Applied Microbiology and John Wiley & Sons Ltd, Environmental Microbiology Reports, 6, 100–105