von Canstein Harald, Ogawa Jun, Shimizu Sakayu, Lloyd Jonathan R
School of Earth, Atmospheric and Environmental Sciences, The University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom.
Appl Environ Microbiol. 2008 Feb;74(3):615-23. doi: 10.1128/AEM.01387-07. Epub 2007 Dec 7.
Fe(III)-respiring bacteria such as Shewanella species play an important role in the global cycle of iron, manganese, and trace metals and are useful for many biotechnological applications, including microbial fuel cells and the bioremediation of waters and sediments contaminated with organics, metals, and radionuclides. Several alternative electron transfer pathways have been postulated for the reduction of insoluble extracellular subsurface minerals, such as Fe(III) oxides, by Shewanella species. One such potential mechanism involves the secretion of an electron shuttle. Here we identify for the first time flavin mononucleotide (FMN) and riboflavin as the extracellular electron shuttles produced by a range of Shewanella species. FMN secretion was strongly correlated with growth and exceeded riboflavin secretion, which was not exclusively growth associated but was maximal in the stationary phase of batch cultures. Flavin adenine dinucleotide was the predominant intracellular flavin but was not released by live cells. The flavin yields were similar under both aerobic and anaerobic conditions, with total flavin concentrations of 2.9 and 2.1 micromol per gram of cellular protein, respectively, after 24 h and were similar under dissimilatory Fe(III)-reducing conditions and when fumarate was supplied as the sole electron acceptor. The flavins were shown to act as electron shuttles and to promote anoxic growth coupled to the accelerated reduction of poorly crystalline Fe(III) oxides. The implications of flavin secretion by Shewanella cells living at redox boundaries, where these mineral phases can be significant electron acceptors for growth, are discussed.
诸如希瓦氏菌属等能够进行铁（III）呼吸的细菌在铁、锰和痕量金属的全球循环中发挥着重要作用，并且在许多生物技术应用中都很有用，包括微生物燃料电池以及对受有机物、金属和放射性核素污染的水体和沉积物进行生物修复。已经提出了几种替代的电子传递途径，用于希瓦氏菌属对不溶性细胞外地下矿物（如铁（III）氧化物）的还原。一种这样的潜在机制涉及电子穿梭体的分泌。在这里，我们首次鉴定出黄素单核苷酸（FMN）和核黄素是一系列希瓦氏菌属产生的细胞外电子穿梭体。FMN的分泌与生长密切相关，且超过核黄素的分泌，核黄素的分泌并非完全与生长相关，而是在分批培养的稳定期达到最大值。黄素腺嘌呤二核苷酸是主要的细胞内黄素，但活细胞不会释放它。在需氧和厌氧条件下，黄素产量相似，24小时后每克细胞蛋白的总黄素浓度分别为2.9和2.1微摩尔，在异化铁（III）还原条件下以及当延胡索酸作为唯一电子受体时，黄素产量也相似。黄素被证明可作为电子穿梭体，并促进缺氧生长，同时加速对结晶性差的铁（III）氧化物的还原。本文讨论了生活在氧化还原边界的希瓦氏菌细胞分泌黄素的意义，在这些边界处，这些矿物相可能是生长的重要电子受体。
