|Wang, Zheng - Naval Research Laboratory|
|Leary, D - Naval Research Laboratory|
|Malanoski, A - Naval Research Laboratory|
|Hervey, W - Naval Research Laboratory|
|Eddie, B - Naval Research Laboratory|
|Vora, G - Naval Research Laboratory|
|Tender, L - Naval Research Laboratory|
|Lin, B - Naval Research Laboratory|
|Strycharz-glaven, S - Naval Research Laboratory|
Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/5/2014
Publication Date: 11/14/2014
Citation: Wang, Z., Leary, D.H., Malanoski, A., Li, R.W., Hervey, W.J., Eddie, B., Vora, G.J., Tender, L.M., Lin, B.C., Strycharz-Glaven, S.M. 2014. A previously uncharacterized, nonphotosynthetic member of the chromatiaceae is the primary CO2-fixing constituent in a self-regenerating biocathode. Applied and Environmental Microbiology. 81:699–712. DOI:10.1128/AEM.02947-14.
Interpretive Summary: The term ‘biocathode’ refers to a biofilm, constituted by a single organism or microbial consortium formed on the cathode of a bioelectrochemical system that consumes electrons. Biocathodes play a key role in microbial fuel cells, a unique type of biofuel cell that produces electric power by utilizing microorganisms. Biocathodes have considerable application potentials, such as in bioenergy production. Although biocathodes hold great potential as a stable electron source to drive microbial metabolism, little is known about the underlying microbial electron transfer (ET) pathways. In this study, we used novel metagenomics and metaproteomics technologies to investigate ET transfer pathways in an autotrophic biocathode biofilm. Our findings demonstrate that microbes in the family Chromatiaceae serve as the primary autotroph while other biofilm constituents, including Marinobacter and Labrenzia, support biofilm ET and carbon cycling. These findings represent the first description of putative ET mechanisms in a multispecies, electrode-grown biofilm and provide potential targets for engineering biocathode biofilms.
Technical Abstract: Cell-electrode electron transfer (ET) in bioelectrochemical systems is thought to occur through mechanisms similar or analogous to metal-reducing or metal-oxidizing bacteria. Such ET processes are desirable for a number of applications, including improving microbially-mediated O2 reduction in microbial fuel cells and bioelectrosynthesis. In this study, we present a metagenomic and metaproteomic chacterization of a stable, autotrophic multispecies biocathode biofilm consuming electricity from an electrode (+310 mV vs. SHE) and fixing CO2 from seawater. Metagenomic analyses identified at least 16 distinct organisms, 15 of which could definitively be assigned to a cluster genome at the family or genus level. A total of 644 proteins were identified from shotgun metaproteomic analysis of the biocathode biofilm, and the data have been deposited to the ProteomeXchange with identifier PXD001045. Cluster genomes could be used to predict the origin of 599 identified proteins, with Marinobacter, Chromatiaceae, Labrenzia, and Kordiimonas being the most represented (177, 137, 59, and 44 proteins respectively). While members of the family Alcanivoraceae are predicted to be the most abundant biofilm constituents, proteomics analysis and RT-PCR confirm an unknown member of the family Chromatiaceae as the most active in relation to biocathode ET and CO2 fixation. 32 key Calvin-Benson-Bassham cycle genes and accessory genes were identified in the biocathode metagenome almost exclusively from the Chromatiaceae cluster genome and 11 of these were confirmed by proteomics. Proteins were also identified from the Chromatiaceae genome cluster with synteny to those suggested as part of an iron oxidation pathway in Zetaproteobacteria, and expression of multiple c-type cytochromes was observed by RT-PCR. Combined, these findings represent the first description of putative ET mechanisms in a multispecies, electrode-grown biofilm and provide potential targets for engineering biocathode biofilms.