Long-term Operation of Microbial Electrosynthesis Systems Improves Acetate Production by Autotrophic Microbiomes

Abstract

Microbial electrosynthesis is the biocathode-driven production of chemicals from CO2 and has the promise to be a sustainable, carbon-consuming technology. To date, microbial electrosynthesis of acetate, the first step in order to generate liquid fuels from CO2, has been characterized by low rates and yields. To improve performance, a previously established acetogenic biocathode was operated in semi-batch mode at a poised potential of -590 mV vs SHE for over 150 days beyond its initial development. Rates of acetate production reached a maximum of 17.25 mM day(-1) (1.04 g L(-1) d(-1)) with accumulation to 175 mM (10.5 g L(-1)) over 20 days. Hydrogen was also produced at high rates by the biocathode, reaching 100 mM d(-1) (0.2 g L(-1) d(-1)) and a total accumulation of 1164 mM (2.4 g L(-1)) over 20 days. Phylogenetic analysis of the active electrosynthetic microbiome revealed a similar community structure to what was observed during an earlier stage of development of the electroacetogenic microbiome. Acetobacterium spp. dominated the active microbial population on the cathodes. Also prevalent were Sulfurospirillum spp. and an unclassified Rhodobacteraceae. Taken together, these results demonstrate the stability, resilience, and improved performance of electrosynthetic biocathodes following long-term operation. Furthermore, sustained product formation at faster rates by a carbon-capturing microbiome is a key milestone addressed in this study that advances microbial electrosynthesis systems toward commercialization.

A Previously Uncharacterized, Nonphotosynthetic Member of the Chromatiaceae Is the Primary CO 2 -Fixing Constituent in a Self-Regenerating Biocathode

“…Proteins prevalent among all the cluster genomes included structural proteins for motility and biofilm formation, such as flagella, type IV pili, fimbria, and chemotaxis. Members of the order Rhodobacterales, which includes Phaeobacter, Labrenzia, and Hyphomonas spp., have been reported to be ubiquitous and dominant primary surface colonizers of biocorroding communities in temperate coastal waters (72) and deep-sea environments (23) and to be significantly abundant in acetogenic multispecies biocathodes (16). The Kordiimonas genome cluster was highly represented among the Alphaproteobacteria; however, the role of the organism within the biocathode community is also not clear.…”

“…Little effort has been put into developing microbial consortia as biocathode catalysts, even though they have been shown to outperform homogeneous bacterial populations in terms of current density (15). Marshall et al (3,16) have demonstrated long-term biocommodity production using an acetogenic biocathode consortium but have not yet reported on the underlying EET pathways. Attempts to cultivate isolates from biocathode environmental enrichments typically result in loss of the electrochemical phenotype (4), as individual biofilm constituents may lack some essential cofactor provided by life in a consortium, such as vitamins or amino acids.…”

Enhanced microbial electrosynthesis by using defined co-cultures

“…Often, sulfate reducers such as Desulfovibrio sp. are also present in these enrichments (Marshall et al, 2013;LaBelle et al, 2014;Patil et al, 2015), suggesting that hydrogen produced by the sulfate reducers might have a role in these biofilms. However, the role of individual strains in mixed communities and the molecular mechanism of microbial electron uptake from the cathode is unclear in most cases.…”

Enrichment of a High-Current Density Denitrifying Microbial Biocathode

“…5,6,[10][11][12] Little is known about the underlying EET mechanisms of biocathodes because cultivation of cathode microorganisms is challenging and typically requires complicating modifications to nutrients and reactor conditions to enable biofilm formation and catalysis that are not required by microbial bioanodes. 13 Only recently has an organism been identified (Mariprofundus ferrooxydans) that can grow on a cathode without such manipulation from pure culture, 13 potentially providing a model system for study analogous to Geobacter sulfurreducens for microbial bioanodes.…”