Storck Tomas, Virdis Bernardino, Batstone Damien J
Advanced Water Management Centre, The University of Queensland, Brisbane, Queensland, Australia.
Centre for Microbial Electrochemical Systems, The University of Queensland, Brisbane, Queensland, Australia.
ISME J. 2016 Mar;10(3):621-31. doi: 10.1038/ismej.2015.139. Epub 2015 Nov 6.
Interspecies electron transfer (IET) is important for many anaerobic processes, but is critically dependent on mode of transfer. In particular, direct IET (DIET) has been recently proposed as a metabolically advantageous mode compared with mediated IET (MIET) via hydrogen or formate. We analyse relative feasibility of these IET modes by modelling external limitations using a reaction-diffusion-electrochemical approach in a three-dimensional domain. For otherwise identical conditions, external electron transfer rates per cell pair (cp) are considerably higher for formate-MIET (317 × 10(3) e(-) cp(-1) s(-1)) compared with DIET (44.9 × 10(3) e(-) cp(-1) s(-1)) or hydrogen-MIET (5.24 × 10(3) e(-) cp(-1) s(-1)). MIET is limited by the mediator concentration gradient at which reactions are still thermodynamically feasible, whereas DIET is limited through redox cofactor (for example, cytochromes) activation losses. Model outcomes are sensitive to key parameters for external electron transfer including cofactor electron transfer rate constant and redox cofactor area, concentration or count per cell, but formate-MIET is generally more favourable for reasonable parameter ranges. Extending the analysis to multiple cells shows that the size of the network does not strongly influence relative or absolute favourability of IET modes. Similar electron transfer rates for formate-MIET and DIET can be achieved in our case with a slight (0.7 kJ mol(-1)) thermodynamic advantage for DIET. This indicates that close to thermodynamic feasibility, external limitations can be compensated for by improved metabolic efficiency when using direct electron transfer.
种间电子转移（IET）对许多厌氧过程都很重要，但关键取决于转移方式。特别是，与通过氢气或甲酸盐的介导种间电子转移（MIET）相比，直接种间电子转移（DIET）最近被认为是一种代谢优势模式。我们通过在三维域中使用反应 - 扩散 - 电化学方法对外部限制进行建模，来分析这些种间电子转移模式的相对可行性。在其他条件相同的情况下，每细胞对（cp）的外部电子转移速率，甲酸盐介导的种间电子转移（317×10³ e⁻ cp⁻¹ s⁻¹）比直接种间电子转移（44.9×10³ e⁻ cp⁻¹ s⁻¹）或氢气介导的种间电子转移（5.24×10³ e⁻ cp⁻¹ s⁻¹）要高得多。介导种间电子转移受反应仍具有热力学可行性的介质浓度梯度限制，而直接种间电子转移则受氧化还原辅因子（例如细胞色素）活化损失的限制。模型结果对外部电子转移的关键参数敏感，包括辅因子电子转移速率常数和氧化还原辅因子面积、每细胞的浓度或数量，但在合理的参数范围内，甲酸盐介导的种间电子转移通常更有利。将分析扩展到多个细胞表明，网络大小对种间电子转移模式的相对或绝对优势影响不大。在我们的案例中，甲酸盐介导的种间电子转移和直接种间电子转移可以实现相似的电子转移速率，直接种间电子转移具有轻微（0.7 kJ mol⁻¹）的热力学优势。这表明在接近热力学可行性时，使用直接电子转移时，外部限制可以通过提高代谢效率来补偿。
