Pester Michael, Knorr Klaus-Holger, Friedrich Michael W, Wagner Michael, Loy Alexander
Department of Microbial Ecology, Vienna Ecology Center, Faculty of Life Sciences, University of Vienna Wien, Austria.
Front Microbiol. 2012 Feb 28;3:72. doi: 10.3389/fmicb.2012.00072. eCollection 2012.
Freshwater wetlands are a major source of the greenhouse gas methane but at the same time can function as carbon sink. Their response to global warming and environmental pollution is one of the largest unknowns in the upcoming decades to centuries. In this review, we highlight the role of sulfate-reducing microorganisms (SRM) in the intertwined element cycles of wetlands. Although regarded primarily as methanogenic environments, biogeochemical studies have revealed a previously hidden sulfur cycle in wetlands that can sustain rapid renewal of the small standing pools of sulfate. Thus, dissimilatory sulfate reduction, which frequently occurs at rates comparable to marine surface sediments, can contribute up to 36-50% to anaerobic carbon mineralization in these ecosystems. Since sulfate reduction is thermodynamically favored relative to fermentative processes and methanogenesis, it effectively decreases gross methane production thereby mitigating the flux of methane to the atmosphere. However, very little is known about wetland SRM. Molecular analyses using dsrAB [encoding subunit A and B of the dissimilatory (bi)sulfite reductase] as marker genes demonstrated that members of novel phylogenetic lineages, which are unrelated to recognized SRM, dominate dsrAB richness and, if tested, are also abundant among the dsrAB-containing wetland microbiota. These discoveries point toward the existence of so far unknown SRM that are an important part of the autochthonous wetland microbiota. In addition to these numerically dominant microorganisms, a recent stable isotope probing study of SRM in a German peatland indicated that rare biosphere members might be highly active in situ and have a considerable stake in wetland sulfate reduction. The hidden sulfur cycle in wetlands and the fact that wetland SRM are not well represented by described SRM species explains their so far neglected role as important actors in carbon cycling and climate change.
淡水湿地是温室气体甲烷的主要来源，但同时也可作为碳汇。在未来几十年到几个世纪里，它们对全球变暖和环境污染的响应是最大的未知因素之一。在本综述中，我们强调了硫酸盐还原微生物（SRM）在湿地相互交织的元素循环中的作用。尽管湿地主要被视为产甲烷环境，但生物地球化学研究揭示了湿地中一个此前未被发现的硫循环，该循环能够维持硫酸盐小驻留池的快速更新。因此，异化硫酸盐还原作用（其发生速率通常与海洋表层沉积物相当）可在这些生态系统的厌氧碳矿化过程中贡献高达36% - 50%。由于相对于发酵过程和产甲烷作用，硫酸盐还原在热力学上更占优势，它有效地减少了甲烷的总产生量，从而减少了甲烷向大气中的排放通量。然而，人们对湿地SRM知之甚少。使用dsrAB[编码异化（双）亚硫酸盐还原酶的亚基A和B]作为标记基因的分子分析表明，与已知SRM无关的新系统发育谱系成员在dsrAB丰富度中占主导地位，并且在含dsrAB的湿地微生物群中也大量存在（如果进行检测的话）。这些发现表明存在迄今未知的SRM，它们是本地湿地微生物群的重要组成部分。除了这些数量上占主导的微生物外，最近一项对德国泥炭地SRM的稳定同位素探测研究表明，稀有生物圈成员可能在原位具有很高的活性，并且在湿地硫酸盐还原中占有相当大的份额。湿地中隐藏的硫循环以及湿地SRM未被已描述的SRM物种很好地代表这一事实，解释了它们迄今作为碳循环和气候变化中重要参与者而被忽视的角色。
