Electrosynthesis of Organic Compounds from Carbon Dioxide Is Catalyzed by a Diversity of Acetogenic Microorganisms

Abstract

Microbial electrosynthesis, a process in which microorganisms use electrons derived from electrodes to reduce carbon dioxide to multicarbon, extracellular organic compounds, is a potential strategy for capturing electrical energy in carbon-carbon bonds of readily stored and easily distributed products, such as transportation fuels. To date, only one organism, the acetogen Sporomusa ovata, has been shown to be capable of electrosynthesis. The purpose of this study was to determine if a wider range of microorganisms is capable of this process. Several other acetogenic bacteria, including two other Sporomusa species, Clostridium ljungdahlii, Clostridium aceticum, and Moorella thermoacetica, consumed current with the production of organic acids. In general acetate was the primary product, but 2-oxobutyrate and formate also were formed, with 2-oxobutyrate being the predominant identified product of electrosynthesis by C. aceticum. S. sphaeroides, C. ljungdahlii, and M. thermoacetica had high (>80%) efficiencies of electrons consumed and recovered in identified products. The acetogen Acetobacterium woodii was unable to consume current. These results expand the known range of microorganisms capable of electrosynthesis, providing multiple options for the further optimization of this process.

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

“…This rate of acetate production is 2-20 times higher than previously reported rates for microbial electrosynthesis [18,19,30]. The contribution of hydrogen and acetate production reactions to the total electron recovery is presented in Fig.…”

“…Ten milliliters of activated sludge and 130 ml of medium were introduced into the cathode chamber. The medium contained the following (per liter of distilled water): 10.92 g Na 2 HPO 4 ·12H 2 O, 3.04 g KH 2 PO 4 , 2.25 g NaCl, 0.5 g MgSO 4 ·7H 2 O, 0.5 g NH 4 Cl, 0.25 g CaCl 2 , 4.0 g NaHCO 3 , 1.0 g yeast extract, 2.11 g 2-bromoethanosulfonic acid, 10 ml of trace metal solution [17], and 10 ml of vitamin solution [18]. To the anode chamber was added 140 ml of the same medium omitting yeast extract and it was flushed with ultrapure CO 2 (purity > 99.999%).…”

“…Interestingly, the acetogen Acetobacterium woodii was unable to consume current [18,19]. Methanogenic and acetogenic bacteria usually share the same ecosystem [1,15].…”

“…The reduction of carbon dioxide in BESs may be a promising way to simultaneously reduce carbon dioxide emissions and generate fuels or other organic compounds [3,9,11,13,18,19,28], which is significant in terms of the environment, energy, and resources.…”

Biofilm conductivity is a decisive variable for high-current-density Geobacter sulfurreducens microbial fuel cells

“…These findings help resolve the previous uncertainty over the relationship between biofilm conductivity and the capacity for current production that arose due to indirect inference of biofilm conductivity, rather than direct measurements. With the method for simultaneously measuring biofilm conductivity and potential losses described here it should be possible to evaluate the conductivity of current-producing biofilms of other pure culture cultures or mixed microbial communities in order to gain further insight into the role of biofilm conductivity in promoting current production in microbial fuel cells or microbe-electrode electron exchange in cathodic processes 37 such as microbial electrosynthesis 38,39 or hydrogen production. 40 Biofilm conductivity appears to be an integral part of electron transport for current production and higher biofilm conductivity facilitates enhanced rates of extracellular electron transfer.…”