Turick Charles E, Tisa Louis S, Caccavo Frank
Department of Microbiology University of New Hampshire, Durham, New Hampshire 03824-2617, USA.
Appl Environ Microbiol. 2002 May;68(5):2436-44. doi: 10.1128/AEM.68.5.2436-2444.2002.
Dissimilatory metal-reducing bacteria (DMRB) utilize numerous compounds as terminal electron acceptors, including insoluble iron oxides. The mechanism(s) of insoluble-mineral reduction by DMRB is not well understood. Here we report that extracellular melanin is produced by Shewanella algae BrY. The extracted melanin served as the sole terminal electron acceptor. Upon reduction the reduced, soluble melanin reduced insoluble hydrous ferric oxide in the absence of bacteria, thus demonstrating that melanin produced by S. algae BrY is a soluble Fe(III)-reducing compound. In the presence of bacteria, melanin acted as an electron conduit to Fe(III) minerals and increased Fe(III) mineral reduction rates. Growth of S. algae BrY occurred in anaerobic minimal medium supplemented with melanin extracted from previously grown aerobic cultures of S. algae BrY. Melanin produced by S. algae BrY imparts increased versatility to this organism as a soluble Fe(III) reductant, an electron conduit for iron mineral reduction, and a sole terminal electron acceptor that supports growth.
异化金属还原菌（DMRB）利用多种化合物作为末端电子受体，包括不溶性铁氧化物。DMRB还原不溶性矿物质的机制尚不清楚。在此我们报告，希瓦氏菌BrY可产生胞外黑色素。提取的黑色素作为唯一的末端电子受体。还原后，还原态的可溶性黑色素在无细菌的情况下可还原不溶性水合氧化铁，从而证明希瓦氏菌BrY产生的黑色素是一种可溶性Fe(III)还原化合物。在有细菌存在的情况下，黑色素作为电子传递体作用于Fe(III)矿物质并提高了Fe(III)矿物质的还原速率。希瓦氏菌BrY在添加了从之前好氧培养的希瓦氏菌BrY中提取的黑色素的厌氧基本培养基中生长。希瓦氏菌BrY产生的黑色素使该生物体作为可溶性Fe(III)还原剂、铁矿物质还原的电子传递体以及支持生长的唯一末端电子受体具有更高的通用性。
