Abstract
Anode-assisted fermentations offer the benefit of an anoxic fermentation routine that can be applied to produce end-products with an oxidation state independent from the substrate. The whole cell biocatalyst transfers the surplus of electrons to an electrode that can be used as a non-depletable electron acceptor. So far, anode-assisted fermentations were shown to provide high carbon efficiencies but low space-time yields. This study aimed at increasing space-time yields of an Escherichia coli-based anode-assisted fermentation of glucose to acetoin. The experiments build on an obligate respiratory strain, that was advanced using selective adaptation and targeted strain development. Several transfers under respiratory conditions led to point mutations in the pfl, aceF and rpoC gene. These mutations increased anoxic growth by three-fold. Furthermore, overexpression of genes encoding a synthetic electron transport chain to methylene blue increased the electron transfer rate by 2.45-fold. Overall, these measures and a medium optimization increased the space-time yield in an electrode-assisted fermentation by 3.6-fold.
Highlights
Sustainable bioproduction will be the key to reaching the goal of a socio-economic transition into a bioeconomy
The rate for 50 μmol/L was 0.45 μmol/L/s (Figure 2). This value is equivalent to a theoretical current density of 498.35 mA/m2 under conditions applied in the experiment of Förster et al [22]
This study started with establishing the characteristics of methylene blue reduction kinetics and produactKiMvivtyalu(3e.6o-ffo2l7d3)μthmaotl/cLanwabse easctahbileisvheedd wfoirththtehiwshsotlrea-icnel.l biocatalyst
Summary
Sustainable bioproduction will be the key to reaching the goal of a socio-economic transition into a bioeconomy. A low energy gain for the organisms and a high catabolic production rate accompanied by low anabolic substrate conversion is favorable for fermentation-based biotechnological processes. This can be achieved under anoxic conditions. An elegant trade-off between both strategies was presented by Causey and colleagues In this study, they disconnected oxygen reduction from energy generation by deleting parts of the membrane-bound ATPase (∆atpFH) [1]. They disconnected oxygen reduction from energy generation by deleting parts of the membrane-bound ATPase (∆atpFH) [1] This concept solves the problem of an increasing biomass production rate, it cannot prevent the dissipation of a not negligible amount of energy in the form of heat
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