Department of Organismic and Evolutionary Biology, Harvard University Cambridge, MA, USA.
Department of Marine Sciences, University of Georgia Athens, GA, USA.
Front Microbiol. 2013 Dec 12;4:386. doi: 10.3389/fmicb.2013.00386. eCollection 2013.
Marine hydrocarbon seeps are ecosystems that are rich in methane, and, in some cases, short-chain (C2-C5) and longer alkanes. C2-C4 alkanes such as ethane, propane, and butane can be significant components of seeping fluids. Some sulfate-reducing microbes oxidize short-chain alkanes anaerobically, and may play an important role in both the competition for sulfate and the local carbon budget. To better understand the anaerobic oxidation of short-chain n-alkanes coupled with sulfate-reduction, hydrocarbon-rich sediments from the Gulf of Mexico (GoM) were amended with artificial, sulfate-replete seawater and one of four n-alkanes (C1-C4) then incubated under strict anaerobic conditions. Measured rates of alkane oxidation and sulfate reduction closely follow stoichiometric predictions that assume the complete oxidation of alkanes to CO2 (though other sinks for alkane carbon likely exist). Changes in the δ(13)C of all the alkanes in the reactors show enrichment over the course of the incubation, with the C3 and C4 incubations showing the greatest enrichment (4.4 and 4.5‰, respectively). The concurrent depletion in the δ(13)C of dissolved inorganic carbon (DIC) implies a transfer of carbon from the alkane to the DIC pool (-3.5 and -6.7‰ for C3 and C4 incubations, respectively). Microbial community analyses reveal that certain members of the class Deltaproteobacteria are selectively enriched as the incubations degrade C1-C4 alkanes. Phylogenetic analyses indicate that distinct phylotypes are enriched in the ethane reactors, while phylotypes in the propane and butane reactors align with previously identified C3-C4 alkane-oxidizing sulfate-reducers. These data further constrain the potential influence of alkane oxidation on sulfate reduction rates (SRRs) in cold hydrocarbon-rich sediments, provide insight into their contribution to local carbon cycling, and illustrate the extent to which short-chain alkanes can serve as electron donors and govern microbial community composition and density.
海洋烃类渗漏是富含甲烷的生态系统，在某些情况下还含有短链（C2-C5）和长链烷烃。C2-C4 烷烃，如乙烷、丙烷和丁烷，可能是渗漏流体的重要组成部分。一些硫酸盐还原微生物可以在无氧条件下氧化短链烷烃，它们可能在硫酸盐竞争和局部碳预算方面发挥重要作用。为了更好地了解与硫酸盐还原偶联的短链正烷烃的厌氧氧化，从墨西哥湾（GoM）富含烃类的沉积物中添加了人工补充硫酸盐的海水和四种正烷烃（C1-C4）之一，然后在严格的厌氧条件下培养。烷烃氧化和硫酸盐还原的测量速率与假设烷烃完全氧化为 CO2 的化学计量预测密切相关（尽管烷烃碳可能还有其他汇）。反应器中所有烷烃的δ(13)C 随着培养时间的推移呈富集趋势，其中 C3 和 C4 培养物的富集程度最大（分别为 4.4 和 4.5‰）。溶解无机碳（DIC）中 δ(13)C 的同时消耗意味着碳从烷烃转移到 DIC 库中（C3 和 C4 培养物分别为-3.5 和-6.7‰）。微生物群落分析表明，在培养物降解 C1-C4 烷烃时，类脱卤杆菌的某些成员被选择性富集。系统发育分析表明，在乙烷反应器中富集了不同的基因型，而在丙烷和丁烷反应器中富集的基因型与先前鉴定的 C3-C4 烷烃氧化硫酸盐还原菌一致。这些数据进一步限制了烷烃氧化对冷烃类沉积物中硫酸盐还原速率（SRR）的潜在影响，深入了解了它们对当地碳循环的贡献，并说明了短链烷烃在多大程度上可以作为电子供体，并控制微生物群落组成和密度。
