Speers Allison M, Reguera Gemma
Department of Microbiology and Molecular Genetics, Michigan State University, USA.
Biofilm. 2021 Jun 14;3:100052. doi: 10.1016/j.bioflm.2021.100052. eCollection 2021 Dec.
Oxidative stress greatly limits current harvesting from anode biofilms in bioelectrochemical systems yet insufficient knowledge of the antioxidant responses of electricigens prevents optimization. Using PCA as a model electricigen, we demonstrated enhanced oxygen tolerance and reduced electron losses as the biofilms grew in height on the anode. To investigate the molecular basis of biofilm tolerance, we developed a genetic screening and isolated 11 oxygen-tolerant (oxt) strains from a library of transposon-insertion mutants. The aggregative properties of the oxt mutants promoted biofilm formation and oxygen tolerance. Yet, unlike the wild type, none of the mutants diverted respiratory electrons to oxygen. Most of the oxt mutations inactivated pathways for the detoxification of reactive oxygen species that could have triggered compensatory chronic responses to oxidative stress and inhibit aerobic respiration. One of the mutants (oxt10) also had a growth advantage with Fe(III) oxides and during the colonization of the anode electrode. The enhanced antioxidant response in this mutant reduced the system's start-up and promoted current harvesting from bioanodes even in the presence of oxygen. These results highlight a hitherto unknown role of oxidative stress responses in the stability and performance of current-harvesting biofilms of and identify biological and engineering approaches to grow electroactive biofilms with the resilience needed for practical applications.
氧化应激极大地限制了生物电化学系统中阳极生物膜的电流采集，然而，对产电微生物抗氧化反应的了解不足阻碍了优化。以嗜中性栖热放线菌作为模式产电微生物，我们证明随着生物膜在阳极上生长变厚，其耐氧性增强且电子损失减少。为了研究生物膜耐受性的分子基础，我们开展了遗传筛选，并从转座子插入突变体文库中分离出11株耐氧（oxt）菌株。oxt突变体的聚集特性促进了生物膜形成和耐氧性。然而，与野生型不同，这些突变体均未将呼吸电子转移到氧气上。大多数oxt突变使活性氧解毒途径失活，而活性氧解毒途径可能引发对氧化应激的代偿性慢性反应并抑制有氧呼吸。其中一个突变体（oxt10）在以三氧化二铁为底物生长以及在阳极电极定殖过程中也具有生长优势。该突变体中增强的抗氧化反应缩短了系统启动时间，甚至在有氧存在的情况下也促进了生物阳极的电流采集。这些结果突出了氧化应激反应在产电生物膜稳定性和性能方面迄今未知的作用，并确定了培养具有实际应用所需复原力的电活性生物膜的生物学和工程方法。
