Toward understanding long-distance extracellular electron transport in an electroautotrophic microbial community

Abstract

Here we show that long-distance extracellular electron transport occurs in a cathodic biofilm capable of CO2 fixation and O2 respiration.

Metatranscriptomics Supports the Mechanism for Biocathode Electroautotrophy by “CandidatusTenderia electrophaga”

“…Replicate S2A took 2 days longer. The midpoint potential (E M ) of each BES measured by CV once steady-state current was achieved was similar to that previously reported (9, 10, 13, 19) at ca. 440 mV versus SHE (Table 1).…”

“…Our characterization of the biocathode-MCL community activity by metatranscriptomics supports previous metaproteomic and 16S rRNA amplicon characterizations of biocathode-MCL indicating that there is substantial variability in the abundance of specific bacteria, even between seemingly identical reactors inoculated on the same day with the same inoculum (10, 19). However, the major constituents that are present have been stable for over 6 years, as measured by several methods, including the use of 16S clone libraries, metagenomics, proteomics, 16S amplicon sequencing, and fluorescence in situ hybridization microscopy (9, 10, 13, 19, 20), allowing us to use the previously generated metagenome sequencing data to align the metatranscriptomics data.…”

“…Tenderia electrophaga” (9, 10); therefore, we searched the metatranscriptome for evidence of an EET conduit whose expression might be affected by the change in electrode potential (Table S1). The cyc 2 homolog in “ Ca.…”

“…However, the major constituents that are present have been stable for over 6 years, as measured by several methods, including the use of 16S clone libraries, metagenomics, proteomics, 16S amplicon sequencing, and fluorescence in situ hybridization microscopy (9, 10, 13, 19, 20), allowing us to use the previously generated metagenome sequencing data to align the metatranscriptomics data. This is important for studies where only limited biomass can be recovered from the electrode surface.…”

“…It is proposed that MCL reduces O 2 with electrons supplied solely by the cathode, directing a portion of the acquired energy and electrons for autotrophy. Cyclic voltammetry (CV) revealed a sigmoid-shaped dependency for current associated with catalytic O 2 reduction (turnover current) dependent upon electrode potential (10). It is proposed that this dependency reflects Nernstian behavior of the heterogeneous electron transfer reaction (across the biofilm/electrode interface) that is mediated by a redox cofactor, which is fast, reversible, and not the rate-limiting step in direct electron uptake from the cathode by the biofilm (9, 11, 12).…”