微生物在透水性和粘性沉积物中通过不同途径氧化葡萄糖

Tess F Hutchinson, Adam J Kessler, Wei Wen Wong, Puspitaningsih Hall, Pok Man Leung, Thanavit Jirapanjawat, Chris Greening, Ronnie N Glud, Perran L M Cook
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摘要

在海洋沉积物中,缺氧条件下有机物的微生物降解通常被认为是通过发酵产生挥发性 脂肪酸(VFA),然后通过还原末端电子受体(如硝酸盐、铁、锰和硫酸盐)将其氧化成 CO2。有观点认为,在氧含量变化很大的环境中,由兼性厌氧细菌(与外部末端电子受体不耦合)介导的发酵成为主要过程。在这里,我们首次提出了这种发酵的直接证据,使用的是一种新型的差异标记葡萄糖同位素测定法,它能区分呼吸和发酵产生的二氧化碳。利用这种方法,我们测量了一系列透水性(沙质)和粘性(泥质)沉积物以及四种细菌分离物中葡萄糖呼吸和发酵的相对贡献。在缺氧条件下,适应高能沙质或生物扰动场地的微生物群落通过恩伯登-迈尔霍夫-帕尔纳斯(EMP)途径进行发酵,其方式与厌氧呼吸无关。长期缺氧培养表明,这种脱钩可持续长达 160 小时。与此相反,缺氧泥质沉积物(中位粒径较小)中的微生物群落通常会将 13C 葡萄糖完全氧化为 13CO2,这与经典的氧化还原级联模型一致。我们还意外地观察到,在渗透性沉积物中,发酵是在缺氧条件下进行的。使用从渗透性沉积物中分离出来的四种细菌的纯培养物进一步证实了这些观察结果。我们的研究结果表明,适应多变氧气环境的微生物群落在瞬时缺氧条件下通过与呼吸作用脱钩的发酵代谢葡萄糖(可能还有其他有机分子)。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Microorganisms oxidize glucose through distinct pathways in permeable and cohesive sediments
In marine sediments, microbial degradation of organic matter under anoxic conditions is generally thought to proceed through fermentation to volatile fatty acids (VFA), which are then oxidized to CO2 coupled to the reduction of terminal electron acceptors (e.g. nitrate, iron, manganese and sulfate). It has been suggested that, in environments with a highly variable oxygen regime, fermentation mediated by facultative anaerobic bacteria (uncoupled to external terminal electron acceptors) becomes the dominant process. Here, we present the first direct evidence for this fermentation using a novel differentially-labelled glucose isotopologue assay that distinguishes between CO2 produced from respiration and fermentation. Using this approach, we measured the relative contribution of respiration and fermentation of glucose in a range of permeable (sandy) and cohesive (muddy) sediments, as well as four bacterial isolates. Under anoxia, microbial communities adapted to high energy sandy or bioturbated sites mediate fermentation via the Embden-Meyerhof-Parnas (EMP) pathway, in a manner uncoupled from anaerobic respiration. Prolonged anoxic incubation suggests this uncoupling lasts up to 160 hours. In contrast, microbial communities in anoxic muddy sediments (smaller median grain size) generally completely oxidized 13C glucose to 13CO2, consistent with the classical redox cascade model. We also unexpectedly observed that fermentation occurred under oxic conditions in permeable sediments. These observations were further confirmed using pure cultures of four bacteria isolated from permeable sediments. Our results suggest microbial communities adapted to variable oxygen regimes metabolise glucose (and likely other organic molecules) through fermentation uncoupled to respiration during transient anoxic conditions.
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