Beaton E D, Stevenson Bradley S, King-Sharp Karen J, Stamps Blake W, Nunn Heather S, Stuart Marilyne
Chalk River Laboratories, Canadian Nuclear Laboratories, Chalk River ON, Canada.
Department of Microbiology and Plant Biology, University of Oklahoma, Norman OK, USA.
Front Microbiol. 2016 Dec 6;7:1933. doi: 10.3389/fmicb.2016.01933. eCollection 2016.
Microorganisms found in terrestrial subsurface environments make up a large proportion of the Earth's biomass. Biogeochemical cycles catalyzed by subsurface microbes have the potential to influence the speciation and transport of radionuclides managed in geological repositories. To gain insight on factors that constrain microbial processes within a formation with restricted groundwater flow we performed a meta-community analysis on groundwater collected from multiple discrete fractures underlying the Chalk River Laboratories site (located in Ontario, Canada). Bacterial taxa were numerically dominant in the groundwater. Although these were mainly uncultured, the closest cultivated representatives were from the phenotypically diverse Betaproteobacteria, Deltaproteobacteria, Bacteroidetes, Actinobacteria, Nitrospirae, and Firmicutes. Hundreds of taxa were identified but only a few were found in abundance (>1%) across all assemblages. The remainder of the taxa were low abundance. Within an ecological framework of selection, dispersal and drift, the local and regional diversity revealed fewer taxa within each assemblage relative to the meta-community, but the taxa that were present were more related than predicted by chance. The combination of dispersion at one phylogenetic depth and clustering at another phylogenetic depth suggest both niche (dispersion) and filtering (clustering) as drivers of local assembly. Distance decay of similarity reveals apparent biogeography of 1.5 km. Beta diversity revealed greater influence of selection at shallow sampling locations while the influences of dispersal limitation and randomness were greater at deeper sampling locations. Although selection has shaped each assemblage, the spatial scale of groundwater sampling favored detection of neutral processes over selective processes. Dispersal limitation between assemblages combined with local selection means the meta-community is subject to drift, and therefore, likely reflects the differential historical events that have influenced the current bacterial composition. Categorizing the study site into smaller regions of interest of more closely spaced fractures, or of potentially hydraulically connected fractures, might improve the resolution of an analysis to reveal environmental influences that have shaped these bacterial communities.
在陆地地下环境中发现的微生物构成了地球生物量的很大一部分。由地下微生物催化的生物地球化学循环有可能影响地质处置库中管理的放射性核素的形态和迁移。为了深入了解限制地下水流动受限地层中微生物过程的因素，我们对从位于加拿大安大略省的粉笔河实验室场地下方多个离散裂缝中采集的地下水进行了元群落分析。细菌类群在地下水中在数量上占主导地位。虽然这些主要是未培养的，但最接近的已培养代表来自表型多样的β-变形菌纲、δ-变形菌纲、拟杆菌门、放线菌门、硝化螺旋菌门和厚壁菌门。鉴定出了数百个类群，但在所有群落中只有少数类群大量存在（>1%）。其余类群丰度较低。在选择、扩散和漂变的生态框架内，局部和区域多样性显示每个群落中的类群相对于元群落较少，但存在的类群比随机预测的更相关。在一个系统发育深度的分散和在另一个系统发育深度的聚类相结合，表明生态位（分散）和过滤（聚类）都是局部组装的驱动因素。相似性的距离衰减揭示了1.5公里的明显生物地理学特征。β多样性表明在浅层采样位置选择的影响更大，而在深层采样位置扩散限制和随机性的影响更大。虽然选择塑造了每个群落，但地下水采样的空间尺度有利于检测中性过程而非选择性过程。群落之间的扩散限制与局部选择相结合意味着元群落容易发生漂变，因此，可能反映了影响当前细菌组成的不同历史事件。将研究场地划分为裂缝间距更近或可能水力连通的裂缝的较小感兴趣区域，可能会提高分析的分辨率，以揭示塑造这些细菌群落的环境影响。
