Department of BioSciences, Rice University, Houston, United States.
Biological Nanostructures Facility, The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, United States.
Elife. 2022 Feb 11;11:e70684. doi: 10.7554/eLife.70684.
Energy conservation in microorganisms is classically categorized into respiration and fermentation; however, recent work shows some species can use mixed or alternative bioenergetic strategies. We explored the use of extracellular electron transfer for energy conservation in diverse lactic acid bacteria (LAB), microorganisms that mainly rely on fermentative metabolism and are important in food fermentations. The LAB uses extracellular electron transfer to increase its NAD/NADH ratio, generate more ATP through substrate-level phosphorylation, and accumulate biomass more rapidly. This novel, hybrid metabolism is dependent on a type-II NADH dehydrogenase (Ndh2) and conditionally requires a flavin-binding extracellular lipoprotein (PplA) under laboratory conditions. It confers increased fermentation product yield, metabolic flux, and environmental acidification in laboratory media and during kale juice fermentation. The discovery of a single pathway that simultaneously blends features of fermentation and respiration in a primarily fermentative microorganism expands our knowledge of energy conservation and provides immediate biotechnology applications.
微生物中的能量守恒通常分为呼吸作用和发酵作用；然而，最近的研究表明，有些物种可以使用混合或替代的生物能量策略。我们探索了利用细胞外电子转移来促进不同乳酸细菌（LAB）的能量守恒，这些微生物主要依赖发酵代谢，并且在食品发酵中非常重要。LAB 利用细胞外电子转移来增加 NAD/NADH 比值，通过底物水平磷酸化产生更多的 ATP，并更快速地积累生物量。这种新颖的混合代谢依赖于一种 II 型 NADH 脱氢酶（Ndh2），并且在实验室条件下，条件性地需要一种黄素结合细胞外脂蛋白（PplA）。它在实验室培养基中和在羽衣甘蓝汁发酵过程中，提高了发酵产物产量、代谢通量和环境酸化。在主要进行发酵的微生物中，发现了一条同时融合发酵和呼吸作用特征的单一途径，这扩展了我们对能量守恒的认识，并提供了直接的生物技术应用。
