嗜中性微好氧铁氧化菌研究进展

在弱酸至近中性微氧条件下,嗜中性微好氧铁氧化菌能够通过依赖氧气的呼吸机制将二价亚铁氧化成三价铁,并获得生长所需能量。这一生物铁氧化过程的主要产物之一是无定形羟基氧化铁——一种异化铁还原作用(铁呼吸)的理想底物,故可加速铁元素在氧化还原分界层的地质循环。有关嗜中性微好氧铁氧化菌的记载可追溯到19世纪30年代,但对其生理、生态与系统发育学的研究自20世纪90年代中期才取得显著进展,主要得益于专性铁氧化菌新种、属的成功培养与分离。已知微好氧铁氧化菌广泛分布于弱酸及近中性富铁地下水、湿地和深海等环境,其参与调控的铁氧化过程对铁及其他元素(如碳、氮、磷、锰和砷等)的生物地球化学循环具有重要意义。这类古老微生物在金属成矿、地壳演变、全球气候变化及其它生源要素地球化学过程中的作用研究已逐渐受到关注,正成为地质与环境微生物学领域的研究热点。主要总结国外近15a对嗜中性微好氧铁氧化菌的研究进展,包括其代谢机理、种类和分布、生态学研究方法和技术、以及细菌铁氧化作用的实际应用和环境意义等,并对今后研究方向提出展望。

Recent progress in research on neutrophilic, microaerophilic iron(II)-oxidizing bacteria

Neutrophilic, microaerophilic iron(II)-oxidizing bacteria (FeOB) can oxidize iron(II) for energy via O2-dependent mechanisms under suboxic, slightly-acidic to circumneutral conditions. This biological oxidation process commonly produces copious amorphous iron(III) oxyhydroxides, a preferential substrate for dissimilatory iron(III) reduction (iron respiration). Such oxyhydroxides have the potential to accelerate iron geochemical cycling at redox interfaces in terrestrial and aquatic systems. Despite reports on neutrophilic, microaerophilic FeOB since the 1830s, associated research progress has been slow, largely due to difficulty in laboratory cultivation and isolation of these organisms. Until the mid-1990s, modified FeS gradient methods were used for isolation of novel obligate FeOB from diverse habitats and substantial progress was achieved in understanding bacterial iron(II) oxidation. Representative neutrophilic, microaerophilic FeOB include stalked Gallionella and Mariprofundus, sheathed Leptothrix and Sphaerotilus, and several non-stalk-forming, unicellular species such as Sideroxidans, Ferritrophicum and Ferrocurvibacter. Related species have frequently been found in redox transition zones of circumneutral-pH, iron-rich environments such as groundwater seeps, wetland rhizosphere soils and deep-sea hydrothermal vents. Bacterial iron(II) oxidation is of global significance to biogeochemical iron cycling and other elements such as C, N, P, S and Mn. Bacterially-mediated iron cycling also influences the fate and transport of organic compounds and several trace metals. There is growing interest in understanding the role of neutrophilic, microaerophilic FeOB in biomineralization, geologic evolution, global climate change, and other fundamental geochemical processes. Here we review recent findings regarding bacterial iron(II) oxidation under suboxic, circumneutral-pH conditions, and summarize associated methodologies for studying the ecology of neutrophilic, microaerophilic FeOB. Recommendations are provided regarding future study of these organisms and associated biogeochemical processes.