Electrosynthesis of Commodity Chemicals by an Autotrophic Microbial Community

Abstract

A microbial community originating from brewery waste produced methane, acetate, and hydrogen when selected on a granular graphite cathode poised at ؊590 mV versus the standard hydrogen electrode (SHE) with CO 2 as the only carbon source. This is the first report on the simultaneous electrosynthesis of these commodity chemicals and the first description of electroacetogenesis by a microbial community. Deep sequencing of the active community 16S rRNA revealed a dynamic microbial community composed of an invariant Archaea population of Methanobacterium spp. and a shifting Bacteria population. Acetobacterium spp. were the most abundant Bacteria on the cathode when acetogenesis dominated. Methane was generally the dominant product with rates increasing from <1 to 7 mM day ؊1 (per cathode liquid volume) and was concomitantly produced with acetate and hydrogen. Acetogenesis increased to >4 mM day ؊1 (accumulated to 28.5 mM over 12 days), and methanogenesis ceased following the addition of 2-bromoethanesulfonic acid. Traces of hydrogen accumulated during initial selection and subsequently accelerated to >11 mM day ؊1 (versus 0.045 mM day ؊1 abiotic production). The hypothesis of electrosynthetic biocatalysis occurring at the microbe-electrode interface was supported by a catalytic wave (midpoint potential of ؊460 mV versus SHE) in cyclic voltammetry scans of the biocathode, the lack of redox active components in the medium, and the generation of comparatively high amounts of products (even after medium exchange). In addition, the volumetric production rates of these three commodity chemicals are marked improvements for electrosynthesis, advancing the process toward economic feasibility. T he U.S. economy is heavily reliant on the use of fossil-based carbon to produce many commodity chemicals and fuels. However, due to supply difficulties, the inevitable decline of these resources, increased world demand, and environmental concerns, a shift away from coal and oil to alternative energy sources such as natural gas, solar, and wind is occurring. However, most of these energy sources are either limited by fluctuations in price and availability or are nonrenewable, as in the case of natural gas. These factors have encouraged research into the development of renewable energy technologies powered by microbes. Of particular interest are microorganisms that can capture the global greenhouse gas CO 2 and convert it to a valuable commodity such as a fuel.Bioelectrochemical systems (BESs) include microbial fuel cells (MFCs), microbial electrolysis cells (MECs), and electrosynthetic biocathodes (4,17,18,27). Of these, the bioanodes of MFCs and MECs have been the most intensively investigated. The newest and arguably most promising of these technologies is the generation of valuable chemicals by electrosynthesis. Microbial electrosynthesis requires microorganisms to catalyze the reduction of CO 2 by consuming electrons on a cathode in a BES.The purpose of the present study was to establish a sustainable biocathode from a mixed microbi...

Production of Acetate from Carbon Dioxide in Bioelectrochemical Systems Based on Autotrophic Mixed Culture

“…Therefore, the total electron recovery of this process was mostly due to acetate formation. Simultaneous production of acetate and methane from carbon dioxide in BESs was observed by Marshall et al [14] and in our previous study [8]. However, methanogenesis out-competed acetogenesis, and methane has a high global warming potential.…”

“…This result is similar to a report in which the operational biocathode was treated with 2-bromoethanesulfonic acid; long rod-shaped microbes became less prevalent while thicker rod-shaped microbes became the dominant, morphology on the electrode. Furthermore, the total amount of microorganisms was less on the cathode [14].…”

“…The possibility of simultaneously producing methane and acetate from carbon dioxide in BESs based on mixed cultures has been reported only very recently, both by Marshall et al [14] and in our previous study [8]. Marshall et al [14] observed that Methanobacterium spp. and Acetobacterium spp.…”

“…Pure cultures of W. succinogenes have shown perchlorate-degrading activity in the presence of added hydrogen [29]. Members of the genus Wolinella were also present in BESs for the simultaneous production of methane and acetate [14]. A. woodii is a Na + -dependent acetogen, lacking cytochromes but having membrane-bound corrinoids [16] and a carbon-conserving mechanism by means of a Na + -dependent ATPase [4].…”

Enhanced microbial electrosynthesis by using defined co-cultures

“…Microbial strains that facilitate electron uptake from a cathodic surface and supply electrons to the surrounding community can, therefore, be considered ecosystem engineers. Although this possibility has already been mentioned in one of the first studies on electrosynthesis by mixed species biofilms (Marshall et al, 2012), it lacked evidence for single strains catalyzing hydrogen formation at high rate. Based on the high cellular electron uptake rates (410 6 e − s − 1 cell − 1 ), even a relatively small number of electroactive cells could result in substantial current consumption rates and thereby provide an effective electron donor for a diverse microbial ecosystem.…”