微生物在地球化学铁循环过程中的作用

The Role of Microorganisms in the Geochemical Iron Cycle

铁元素虽然只在地壳含量中位列第4,但却是地球上分布最广的变价金属元素之一,微生物介导的铁循环及其与生源要素碳、氮、氧和硫等耦合的氧化还原反应是微生物地球化学循环的重要驱动力.由于铁循环过程中氧化态三价铁Fe(Ⅲ)在环境p H条件下大多以不溶状态存在,因而由其参与的地球化学循环进程通常较为缓慢.研究表明,微生物在铁元素的地球化学循环过程中起着举足轻重的作用,并在该过程中参与矿物的生成与转化.近年来的最新研究发现,参与地球化学铁循环的微生物之间,微生物与矿物之间,以及矿物介导的微生物之间存在着多样的相互作用,而含铁矿物介导的微生物胞外电子传递机制是其中最受瞩目的研究热点.本文综述了微生物介导的地球化学铁循环过程的类型及其过程中的主导微生物,并针对铁还原过程中已知的微生物胞外电子传递机制做了介绍.文中涉及的微生物地球化学铁循环过程中的各种相互作用,已经成为相关研究领域的热点问题,最新研究结果将为进一步阐明微生物地球化学铁循环过程、机制及其环境效应提供重要的理论依据和研究基础.

Iron, the fourth most abundant element in Earth＇s crust, is also one of the most abundant variable valence metal elements. Redox reactions of Fe with C, N, O, and S drive the global biogeochemical cycles. Because of the limited solubility of ferric Fe in the environment, the speed of cycles involving ferric Fe is usually slow. Numerous results have shown that microbes play a significant role in the iron biogeochemical cycles including the formation and transformation of iron minerals. Recently, various interactions between microbes and iron minerals have been reported, especially the interplay between microbes in the presence or absence of iron minerals. Among them, the most dramatic topic is the study focusing on the microbial extracellular electron transfer mediated by iron minerals. In this review, we discuss different kinds of microbial geochemical iron cycles and the representative microbial species during the cycling. We also present the mechanism of microbial extracellular electron transfer, in the currently best-known form. The interactions between microbes and iron minerals, as a fascinating topic for this review, cast new light on further mechanisms and potential environmental effects of the microbial geochemical iron cycles.