Department of Microbiology and Immunology, University of Melbourne, Parkville, Victoria 3010, Australia.
Appl Environ Microbiol. 2010 Mar;76(5):1471-9. doi: 10.1128/AEM.02072-09. Epub 2010 Jan 8.
Soil is exposed to hydrogen when symbiotic rhizobia in legume root nodules cannot recycle the hydrogen that is generated during nitrogen fixation. The hydrogen emitted is most likely taken up by free-living soil bacteria that use hydrogen as an energy source, though the bacteria that do this in situ remain unclear. In this study, we investigated the effect of hydrogen exposure on the bacteria of two different soils in a microcosm setup designed to simulate hydrogen-emitting root nodules. Although the size and overall composition of the soil bacterial community did not significantly alter after hydrogen exposure, one ribotype increased in relative abundance within each soil. This single-ribotype shift was identified by generating multiple terminal restriction fragment length polymorphism (T-RFLP) profiles of 16S rRNA genes from each soil sample, with gene sequence confirmation to identify terminal restriction fragments. The increased abundance of a single ribotype after hydrogen exposure, within an otherwise similar community, was found in replicate samples taken from each microcosm and was reproducible across replicate experiments. Similarly, only one member of the soil bacterial community increased in abundance in response to hydrogen exposure in soil surrounding the root nodules of field-grown soybean (Glycine max). The ribotypes that increased after hydrogen exposure in each soil system tested were all from known hydrogen-oxidizing lineages within the order Actinomycetales. We suggest that soil actinomycetes are important utilizers of hydrogen at relevant concentrations in soil and could be key contributors to soil's function as a sink in the global hydrogen cycle.
当共生根瘤菌在豆科植物根瘤中无法回收固氮过程中产生的氢气时，土壤就会暴露在氢气中。排放的氢气很可能被自由生活的土壤细菌吸收，这些细菌将氢气作为能源，尽管目前尚不清楚哪些细菌是原位吸收氢气的。在这项研究中，我们在微宇宙设置中研究了氢气暴露对两种不同土壤细菌的影响，该设置旨在模拟排放氢气的根瘤。尽管氢气暴露后土壤细菌群落的大小和整体组成没有显著改变，但每种土壤中的一个菌型相对丰度增加。通过对每个土壤样本的 16S rRNA 基因进行多次末端限制性片段长度多态性（T-RFLP）分析，并通过基因序列确认来鉴定末端限制性片段，从而确定了这种单一菌型的变化。在每个微宇宙中从重复样本中都发现了氢气暴露后，在其他方面相似的群落中，单一菌型的丰度增加，并且在重复实验中具有重现性。同样，在田间生长的大豆（Glycine max）根瘤周围土壤中，只有土壤细菌群落中的一个成员对氢气暴露有反应而增加了丰度。在每个测试的土壤系统中，氢气暴露后增加的菌型都来自放线菌目（Actinomycetales）中已知的产氢谱系。我们认为，土壤放线菌是土壤中相关浓度下氢气的重要利用者，并且可能是土壤作为全球氢循环汇的功能的关键贡献者。
