Schulz Kristin, Hunger Sindy, Brown George G, Tsai Siu M, Cerri Carlos C, Conrad Ralf, Drake Harold L
Department of Ecological Microbiology, University of Bayreuth, Bayreuth, Germany.
Embrapa Florestas, Colombo, Brazil.
ISME J. 2015 Aug;9(8):1778-92. doi: 10.1038/ismej.2014.262. Epub 2015 Jan 23.
The anoxic saccharide-rich conditions of the earthworm gut provide an ideal transient habitat for ingested microbes capable of anaerobiosis. It was recently discovered that the earthworm Eudrilus eugeniae from Brazil can emit methane (CH4) and that ingested methanogens might be associated with this emission. The objective of this study was to resolve trophic interactions of bacteria and methanogens in the methanogenic food web in the gut contents of E. eugeniae. RNA-based stable isotope probing of bacterial 16S rRNA as well as mcrA and mrtA (the alpha subunit of methyl-CoM reductase and its isoenzyme, respectively) of methanogens was performed with [(13)C]-glucose as a model saccharide in the gut contents. Concomitant fermentations were augmented by the rapid consumption of glucose, yielding numerous products, including molecular hydrogen (H2), carbon dioxide (CO2), formate, acetate, ethanol, lactate, succinate and propionate. Aeromonadaceae-affiliated facultative aerobes, and obligate anaerobes affiliated to Lachnospiraceae, Veillonellaceae and Ruminococcaceae were associated with the diverse fermentations. Methanogenesis was ongoing during incubations, and (13)C-labeling of CH4 verified that supplemental [(13)C]-glucose derived carbon was dissimilated to CH4. Hydrogenotrophic methanogens affiliated with Methanobacteriaceae and Methanoregulaceae were linked to methanogenesis, and acetogens related to Peptostreptoccocaceae were likewise found to be participants in the methanogenic food web. H2 rather than acetate stimulated methanogenesis in the methanogenic gut content enrichments, and acetogens appeared to dissimilate supplemental H2 to acetate in methanogenic enrichments. These findings provide insight on the processes and associated taxa potentially linked to methanogenesis and the turnover of organic carbon in the alimentary canal of methane-emitting E. eugeniae.
蚯蚓肠道内富含糖类的缺氧环境为能够进行厌氧生活的摄入微生物提供了理想的临时栖息地。最近发现，来自巴西的真蚓属蚯蚓能排放甲烷（CH4），且摄入的产甲烷菌可能与这种排放有关。本研究的目的是解析真蚓属蚯蚓肠道内容物中产甲烷食物网中细菌和产甲烷菌的营养相互作用。以[(13)C]-葡萄糖作为模型糖类，对蚯蚓肠道内容物中的细菌16S rRNA以及产甲烷菌的mcrA和mrtA（分别为甲基辅酶M还原酶及其同工酶的α亚基）进行基于RNA的稳定同位素探测。葡萄糖的快速消耗促进了伴随的发酵过程，产生了许多产物，包括分子氢（H2）、二氧化碳（CO2）、甲酸、乙酸、乙醇、乳酸、琥珀酸和丙酸。与气单胞菌科相关的兼性需氧菌，以及隶属于毛螺菌科、韦荣球菌科和瘤胃球菌科的专性厌氧菌与多样的发酵过程有关。在培养过程中产甲烷作用持续进行，CH4的(13)C标记证实补充的[(13)C]-葡萄糖衍生碳被异化生成CH4。与甲烷杆菌科和甲烷微菌科相关的氢营养型产甲烷菌与产甲烷作用有关，同样发现与消化链球菌科相关的产乙酸菌也是产甲烷食物网的参与者。在产甲烷的肠道内容物富集物中，H2而非乙酸刺激了产甲烷作用，并且在产甲烷富集物中，产乙酸菌似乎将补充的H2异化为乙酸。这些发现为与产甲烷作用以及排放甲烷的真蚓属蚯蚓消化道中有机碳周转相关的过程及相关分类群提供了见解。
