School of Marine Science and Policy, University of Delaware, Lewes, DE, USA.
ISME J. 2013 Jan;7(1):210-20. doi: 10.1038/ismej.2012.93. Epub 2012 Aug 16.
Very little is known about growth rates of individual bacterial taxa and how they respond to environmental flux. Here, we characterized bacterial community diversity, structure and the relative abundance of 16S rRNA and 16S rRNA genes (rDNA) using pyrosequencing along the salinity gradient in the Delaware Bay. Indices of diversity, evenness, structure and growth rates of the surface bacterial community significantly varied along the transect, reflecting active mixing between the freshwater and marine ends of the estuary. There was no positive correlation between relative abundances of 16S rRNA and rDNA for the entire bacterial community, suggesting that abundance of bacteria does not necessarily reflect potential growth rate or activity. However, for almost half of the individual taxa, 16S rRNA positively correlated with rDNA, suggesting that activity did follow abundance in these cases. The positive relationship between 16S rRNA and rDNA was less in the whole water community than for free-living taxa, indicating that the two communities differed in activity. The 16S rRNA:rDNA ratios of some typically marine taxa reflected differences in light, nutrient concentrations and other environmental factors along the estuarine gradient. The ratios of individual freshwater taxa declined as salinity increased, whereas the 16S rRNA:rDNA ratios of only some typical marine bacteria increased as salinity increased. These data suggest that physical and other bottom-up factors differentially affect growth rates, but not necessarily abundance of individual taxa in this highly variable environment.
关于单个细菌分类群的增长率以及它们如何响应环境通量，我们知之甚少。在这里，我们使用焦磷酸测序技术沿着特拉华湾的盐度梯度，对细菌群落的多样性、结构以及 16S rRNA 和 16S rRNA 基因（rDNA）的相对丰度进行了表征。多样性、均匀度、结构和表层细菌群落的生长速率指数沿着横剖面显著变化，反映了河口淡水和海洋端之间的积极混合。整个细菌群落的 16S rRNA 和 rDNA 相对丰度之间没有正相关关系，这表明细菌的丰度不一定反映潜在的生长速率或活性。然而，对于近一半的单个分类群，16S rRNA 与 rDNA 呈正相关，这表明在这些情况下，活性确实遵循丰度。整个水体群落中 16S rRNA 与 rDNA 的正相关性低于自由生活分类群，这表明这两个群落的活性不同。一些典型海洋分类群的 16S rRNA:rDNA 比值反映了沿河口梯度的光照、营养浓度和其他环境因素的差异。随着盐度的增加，个别淡水分类群的 16S rRNA:rDNA 比值下降，而只有一些典型海洋细菌的 16S rRNA:rDNA 比值随着盐度的增加而增加。这些数据表明，物理和其他自下而上的因素会对个别分类群的生长速率产生不同的影响，但不一定会影响其丰度，在这种高度可变的环境中。
