Role of Outer Membrane Cytochromes in Respiration-Linked Metal Reduction

厌氧呼吸提供了一种在缺氧条件下产生能量的机制。革兰氏阴性杆菌希瓦氏菌MR-1表现出显著的厌氧呼吸通用性，使用几种可溶性化合物和高度不溶性锰（IV）和铁（III）氧化物作为电子受体。因此，细胞必须在电子传递组分和这些细胞外不溶性电子受体之间建立联系。当在厌氧条件下生长时，MR-1在其外膜（OM）中具有高的特异性细胞色素含量。它的两种OM细胞色素，OmcA和OmcB（都是c型和具有脂蛋白一致序列）在Mn（IV）还原中起重要作用，它们的表面暴露对不溶性电子受体的使用具有重要意义。该项目将确定OmcA和OmcB是否为脂蛋白，以及脂质修饰是否对它们定位于OM及其支持电子转移到细胞外电子受体的能力至关重要。Mn（IV）的还原只需要2个电子，但OM细胞色素的十碳胺性质可能有助于优化血红素排列，使电子在OM上转移到不溶性的Mn（IV）。这种“电线”方案意味着特定的血红素对电子传输至关重要。该项目将确定是否需要十胺基OM细胞色素的特定血红素来支持不溶性Mn（IV）的减少。这项研究将显著提高对多血红素细胞色素和细菌金属还原的理解，并将拓宽厌氧呼吸的概念框架，包括通过OM组分与细胞外环境的电子传递联系。

Anaerobic respiration provides a mechanism to generate energy under oxygen-limited conditions. The Gram-negative bacterium Shewanella oneidensis MR-1 exhibits remarkable anaerobic respiratory versatility, using several soluble compounds and highly insoluble manganese(IV) and iron(III) oxides as electron acceptors. Therefore, the cells must establish a link between electron transport components and these extracellular insoluble electron acceptors. When grown under anaerobic conditions, MR-1 has a high specific cytochrome content in its outer membrane (OM). Two of its OM cytochromes, OmcA and OmcB (both c-type and having lipoprotein consensus sequences), have significant roles in Mn(IV) reduction and their surface exposure has important implications for the use of insoluble electron acceptors. The project will determine if OmcA and OmcB are lipoproteins, and if the lipid modification is essential for their localization to the OM and their ability to support electron transfer to extracellular electron acceptors. Mn(IV) reduction requires only 2 electrons, but the decaheme nature of the OM cytochromes may facilitate optimal heme arrangement for electron transfer across the OM to insoluble Mn(IV). This "electric wire" scheme implies that particular hemes are critical for electron transport. The project will determine if particular hemes of a decaheme OM cytochrome are required to support the reduction of insoluble Mn(IV). This research will significantly enhance the understanding of multiheme cytochromes and bacterial metal reduction, and will broaden the conceptual framework of anaerobic respiration to include electron transport links to the extracellular environment through OM components.