ar9b00522_si_001.pdf (294.73 kB)
Microbiome for the Electrosynthesis of Chemicals from Carbon Dioxide
journal contribution
posted on 2019-12-06, 16:41 authored by Edward
V. LaBelle, Christopher W. Marshall, Harold D. MayConspectusThe price for renewable electricity
is rapidly decreasing, and
the availability of such energy is expected to increase in the coming
years. This is a welcomed outcome considering that mitigation of climate
disruption due to the use of fossil carbon is reaching a critical
stage. However, the economy will remain dependent on carbon-based
chemicals and the problem of electricity storage persists. Therefore,
the development of electrosynthetic processes that convert electricity
and CO2 into chemicals and energy dense fuels, perhaps
even food, would be desirable. Electrochemistry has been applied to
the manufacture of many valuable products and at a large industrial
scale, but it is difficult to produce multicarbon chemicals from CO2 by chemistry alone. Being that the biological world possesses
expertise at the construction of C–C bonds, it is being examined
in conjunction with electrochemistry to discover new ways of synthesizing
chemicals from electricity and CO2. One approach is microbial
electrosynthesis.This Account describes the development of
a microbial electrosynthesis
system by the authors. A biocathode consisting of a carbon-based electrode
and a microbial community produced short chain fatty acids, primarily
acetate. The device works by electrolysis of water, but microbes facilitate
electron transfer from the cathode while reducing CO2 by
the Wood–Ljungdahl pathway possessed by an Acetobacterium sp. While this acetogenic microorganism dominates the microbiome
growing on the cathode surface, 13 total species of microbes overall
were ecologically selected on the cathode and genomes for each have
been assembled. The combined species may contribute to the stability
of the microbiome, a common feature of naturally selected microbial
communities. The microbial electrosynthesis system was demonstrated
to operate continuously at a cathode for more than 2 years and could
also be used with intermittent power, thus demonstrating the stability
of the microbiome living at the cathode. In addition to the description
of reactor design and startup procedures, the possible mechanisms
of electron transfer are described in this Account. While mysteries
remain to be solved, much evidence indicates that the microbiome may
facilitate electron transfer by supplying catalyst(s) external to
the bacterial cells and onto the cathode surface. This may be in the
form of a hydrogen-producing catalyst that enhances hydrogen generation
by an inert carbon-based electrode.Through the enrichment of
the electrosynthetic microbiome along
with several modifications in reactor design and operation, the productivity
and efficiency were improved. In addition to the intrinsic value of
the current products, coupling the process with a secondary stage
might be used to produce more valuable products from the acetic acid
stream such as lipids, biocrude oil, or higher value food supplements.
Alternatively, additional work on the mechanism of electron transfer,
reactor design/operation, and modification of the microbes through
synthetic biology, particularly to enhance carbon efficiency into
higher value chemicals, are the needed next steps to advance microbial
electrosynthesis so that it may be used to transform renewable electrons
and CO2 directly into products and help solve the problem
of climate disruption.