University of Georgia, Department of Microbiology, Athens, Georgia, USA.
University of Georgia, Warnell School of Forestry and Natural Resources, Athens, Georgia, USA.
Appl Environ Microbiol. 2019 May 16;85(11). doi: 10.1128/AEM.00188-19. Print 2019 Jun 1.
Small streams and their headwaters are key sources of microbial diversity in fluvial systems and serve as an entry point for bacteria from surrounding environments. Community assembly processes occurring in these streams shape downstream population structure and nutrient cycles. To elucidate the development and stability of microbial communities along the length of a first- through third-order stream, fine-scale temporal and spatial sampling regimes were employed along McNutt Creek in Athens, GA, USA. 16S rRNA amplicon libraries were constructed from samples collected on a single day from 19 sites spanning the first 16.76 km of the stream. To provide context for this spatial study and evaluate temporal variability, selected sites at the stream's upper, mid, and lower reaches were sampled daily for 5 days preceding and following the spatial study. In a second study, three sites at and near the creek's headwaters were sampled daily for 11 days to understand initial bacterioplankton community assembly. Both studies revealed decreasing alpha and beta diversity with increasing downstream distance. These trends were accompanied by the enrichment of a small fraction of taxa found at low abundance in headwater-proximal sites. Similar sets of taxa consistently increased in relative abundance in downstream samples over time scales ranging from 1 day to 1 year, many of which belong to clades known to be abundant in freshwater environments. These results underpin the importance of headwaters as the site of rapid in-stream selection that results in the reproducible establishment of a highly stable community of freshwater riverine bacteria. Headwater streams are critical introduction points of microbial diversity for larger connecting rivers and play key roles in the establishment of taxa that partake in in-stream nutrient cycling. We examined the microbial community composition of a first- through third-order stream using fine-scale temporal and spatial regimes. Our results show that the bacterioplankton community develops rapidly and predictably from the headwater population with increasing total stream length. Along the length of the stream, the microbial community exhibits substantial diversity loss and enriches repeatedly for select taxa across days and years, although the relative abundances of individual taxa vary over time and space. This repeated enrichment of a stable stream community likely contributes to the stability and flexibility of downstream communities.
小溪及其源头是河流系统中微生物多样性的关键来源，也是周围环境中细菌进入的入口。这些溪流中发生的群落组装过程塑造了下游的种群结构和养分循环。为了阐明微生物群落沿着美国佐治亚州雅典市 McNutt 溪的长度的发展和稳定性，采用了精细的时间和空间采样方案。从该溪流的前 16.76 公里范围内的 19 个站点采集的单个日期的样本构建了 16S rRNA 扩增子文库。为了为本空间研究提供背景并评估时间变异性，在空间研究之前和之后的 5 天内，每天对溪流上游、中游和下游的选定站点进行采样。在第二项研究中，每天对溪流源头附近的三个站点进行采样，共 11 天，以了解初始细菌浮游生物群落的组装。这两项研究都表明，随着下游距离的增加，alpha 和 beta 多样性呈下降趋势。这些趋势伴随着在靠近源头的站点低丰度下发现的一小部分分类群的富集。在从 1 天到 1 年的时间尺度上，许多属于已知在淡水环境中丰富的类群的分类群的相对丰度在下游样本中持续增加，这些分类群的相对丰度也在时间尺度上持续增加。这些结果支持了源头作为快速溪流内选择的发生地的重要性，这种选择导致了淡水河流细菌高度稳定群落的可重复建立。源头溪流是更大的连接河流中微生物多样性的关键引入点，并在参与溪流养分循环的分类群的建立中发挥关键作用。我们使用精细的时间和空间方案研究了一条一级至三级溪流的微生物群落组成。我们的结果表明，随着总溪流长度的增加，细菌浮游生物群落从源头种群快速而可预测地发展。沿着溪流的长度，微生物群落表现出大量的多样性丧失，并在几天和几年内反复丰富选择的分类群，尽管个别分类群的相对丰度随时间和空间而变化。这种稳定的溪流群落的反复富集可能有助于下游群落的稳定性和灵活性。
