Centre for Advanced Computational Solutions, Wine, Food & Molecular Bioscience Department, Lincoln University, Ellesmere Junction Road, Lincoln, 7647, New Zealand.
J Biol Eng. 2013 May 29;7(1):14. doi: 10.1186/1754-1611-7-14.
G. 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.
In 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.
The 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.
G. sulfurreducens 是微生物燃料电池（MFC）中用于有机到电能生物转化的最常见微生物之一。在基于这种微生物的 MFC 中，电子可以通过三种方式传送到阳极：1）直接电子转移（DET）模式，其中微生物外膜中还原型 c 型细胞色素的电子被阳极直接氧化；2）介导电子转移（MET）模式，其中以 NADH 形式提供的细胞代谢还原势被靶向作为发电的电子源，借助外源介体；3）一种涉及上述两种电子转移机制（DET 和 MET）的假定混合操作模式。然而，G. sulfurreducens 在这三种操作模式下产生电流的潜力以及提取还原当量的代谢机制尚不清楚。
在这项研究中，我们对基因组规模的代谢网络进行通量平衡分析（FBA），以计算在给定实际养分摄取率的情况下，与反应化学计量学兼容的 G. sulfurreducens 产生电流的基本代谢潜力。我们还开发了一种方法，即通量可变性分析与目标通量最小化（FATMIN），以消除无效的 NADH 循环。我们的研究阐明了在 MET 和混合模式下维持 NADH 以产生电流的可能代谢策略。结果表明，G. sulfurreducens 在 DET 模式下具有高达 3.710 A/gDW 的电流输出潜力，在 MET 模式下为 2.711 A/gDW，在假定的混合 MET 和 DET 模式下为 3.272 A/gDW。与仅依赖于一个贡献反应的 DET 相比，MET 和混合模式在需要高电流产生时分别具有十个和四个反应的优势，因此更具弹性。
DET 模式可以实现比 MET 模式更高的最大电流输出极限，但 MET 模式具有更高的功率输出和更灵活的代谢选择来维持电流。MET 和 DET 模式相互竞争用于发电的代谢资源。
