Analysis of Enhanced Current-Generating Mechanism of Geobacter sulfurreducens Strain via Model-Driven Metabolism Simulation

Abstract

Microbial fuel cells (MFCs) are a class of ideal technologies that function via anaerobic respiration of electricigens, which bring current generation and environmental restoration together. An in-depth understanding of microbial metabolism is of great importance in engineering microbes to further improve their respiration. We employed flux balance analysis and selected Fe(iii) as a substitute for the electrode to simulate current-generating metabolism of Geobacter sulfurreducens PCA with a fixed acetate uptake rate. Simulation results indicated the fluxes of reactions directing acetate towards dissimilation to generate electrons increased under the suboptimal growth condition, resulting in an increase in the respiration rate and a decrease in the growth rate. The results revealed the competitive relationship between oxidative respiration and cell growth during the metabolism of microbe current generation. The results helped us quantitatively understand why microbes growing slowly have the potential to make good use of fuel in MFCs. At the same time, slow growth does not necessarily result in speedy respiration. Alternative respirations may exist under the same growth state due to redundant pathways in the metabolic network. The big difference between the maximum and minimum respiration mainly results from the total formate secretion. With iterative flux variability analysis, a relatively ideal model of variant of G. sulfurreducens PCA was reconstructed by deleting several enzymes in the wild model, which could reach simultaneous suboptimal growth and maximum respiration. Under this ideal condition, flux towards extracellular electron transfer rather than for biosynthesis is beneficial for the conversion of organic matter to electricity without large accumulations of biomass and electricigens may maximize utilization of limited fuel. Our simulations will provide an insight into the enhanced current-generating mechanism and identify theoretical range of respiration rates for guiding strain improvement in MFCs.

Performance Modelling of the Bioelectrochemical Glycerol Oxidation by a Co‐Culture of Geobacter Sulfurreducens and Raoultella Electrica

“…The obtained experimental data outlined above were combined with genomic data from R. electrica and from G. sulfurreducens . Possible metabolic pathways from glycerol oxidation to current production by the co‐culture of R. electrica – G .…”

“…(2012) and Meng et al . (2013) were combined for the deduction of shown pathways. ACS: acetyl‐CoA synthetase, ADH: alcohol dehydrogenase, AK: acetate kinase, FDH: formate dehydrogenase, FHL: formate hydrogen‐lyase, FRD: fumarate reductase; GK: glycerol kinase, NDH: NADH dehydrogenase; OMC: outer membrane cytochromes; PFL: pyruvate formate lyase, PK: pyruvate kinase, PTA: phosphate acetyltransferase; Qox: one of two putative quinol oxidases …”

“…The pathways of G. sulfurreducens displayed in Figure were based on the in silico predictions of the central metabolism by Meng et al . (2013) and genomic data . After the uptake of acetate and its conversion into acetyl‐CoA, which enters the incomplete TCA cycle, eight electrons per acetate molecule must be released and transferred to the anode by direct extracellular electron transfer mechanisms.…”

Comparative metabolic state of microflora on the surface of the anode electrode in a microbial fuel cell operated at different pH conditions

“…Geobacter cells reportedly down-regulate gluconeogenesis during electricity generation (Meng et al 2013; Song et al 2016). Because G. sulfurreducens cells cannot directly utilize glucose (Mahadevan et al 2006), we can separate the phases of current production by microflora into an acetate-producing phase from starch via glycolysis, and a current-producing phase from acetate via the TCA cycle.…”

“…ATP is produced in the respiratory electron transfer chain and oxidative consumption of NADH occurs when electricity generation is high in Geobacter species (Meng et al 2013). ATP is also produced in the EM pathway by substrate level phosphorylation.…”