Model-driven elucidation of the inherent capacity of Geobacter sulfurreducens for electricity generation

Abstract

BackgroundG. sulfurreducens is one of the commonest microbes used in microbial fuel cells (MFCs) for organic-to-electricity biotransformation. In MFCs based on this microorganism, electrons can be conveyed to the anode via three ways: 1) direct electron transfer (DET) mode, in which electrons of reduced c-type cytochromes in the microbial outer membrane are directly oxidized by the anode; 2) mediated electron transfer (MET) mode, in which the reducing potential available from cell metabolism in the form of NADH is targeted as an electron source for electricity generation with the aid of exogenous mediators; and 3) a putative mixed operation mode involving both electron transfer mechanisms described above (DET and MET). However, the potential of G. sulfurreducens for current output in these three operation modes and the metabolic mechanisms underlying the extraction of the reducing equivalents are still unknown.ResultsIn this study, we performed flux balance analysis (FBA) of the genome-scale metabolic network to compute the fundamental metabolic potential of G. sulfurreducens for current output that is compatible with reaction stoichiometry, given a realistic nutrient uptake rate. We also developed a method, flux variability analysis with target flux minimization (FATMIN) to eliminate futile NADH cycles. Our study elucidates the possible metabolic strategies to sustain the NADH for current production under the MET and Mixed modes. The results showed that G. sulfurreducens had a potential to output current at up to 3.710 A/gDW for DET mode, 2.711 A/gDW for MET mode and 3.272 A/gDW for a putative mixed MET and DET mode. Compared with DET, which relies on only one contributing reaction, MET and Mixed mode were more resilient with ten and four reactions respectively for high current production.ConclusionsThe DET mode can achieve a higher maximum limit of the current output than the MET mode, but the MET has an advantage of higher power output and more flexible metabolic choices to sustain the electric current. The MET and DET modes compete with each other for the metabolic resource for the electricity generation.

The Problem of Futile Cycles in Metabolic Flux Modeling: Flux Space Characterization and Practical Approaches to Its Solution

“…Although the explanation above referred to fluxes along individual pathwaysin effect, EMs-the strength of the FATMIN method is that these do not in fact [82] have to be identified to apply the method. Simply adding FluxMin to the network and minimizing its flux ensures that the cyclic components implicitly contained in it are eliminated.…”

Microbial Electrochemical Systems with Future Perspectives using Advanced Nanomaterials and Microfluidics

“…The first and second process (photosystem I and II or "Z scheme" [21][22][23] is directly connected with the light catching/electron transfer and the transformation of energy in form of ATP and NADPH. [29][30][31] Mixed direct and indirect EET process have been reported, [32][33][34][35][36][37] and increasing mediator concentration enhances indirect EET, which in turn improves the output power. [21][22][23] The third process (Calvin cycle) uses these energy and reduction equivalents to transform and reduce carbon dioxide to carbohydrates.…”

Theoretical exploration of optimal metabolic flux distributions for extracellular electron transfer by

“…Previously, we have examined the maximum potential of G. sulfurreducens for MFC electricity generation [33]. The comparison of the two microbes shows that G. sulfurreducens has a higher capability for the DET mode current production, at 3.710 A/gDW with a coulombic efficiency of 96.12%.…”