Department of Marine Sciences, University of Georgia, Athens, GA, 30602, USA.
Environ Microbiol Rep. 2014 Apr;6(2):167-72. doi: 10.1111/1758-2229.12129. Epub 2013 Dec 5.
A fundamental question in marine microbial ecology is how microbes adapt to ocean environments. Although numerically dominant populations are typically considered more successful, higher census population sizes (Nc) do not equate directly to a greater capability for adaptation. Instead, effective population size (Ne) determines the fate of deleterious and favourable mutations, and thus is a key parameter for determining the adaptive potential of a population. In the case of the SAR11 and Roseobacter lineages, two abundant heterotrophic bacteria in ocean surface waters with contrasting life history strategies, culture-independent population surveys suggest that SAR11s have greater Nc than Roseobacters. To determine relative Ne, we compared the ratio of nonsynonymous to synonymous substitution rates (ω) of recently diverged lineages of these taxa. Values of ω associated with several of the Roseobacter subclades were lower than for SAR11 subclades, suggesting greater Ne in these cases. Most Roseobacter lineages also had smaller ω values compared with an atypical basal Roseobacter lineage with a large Nc. This finding provides insight into variability in Ne across two important marine bacterial lineages, and provides an evolutionary context for considering how heterotrophic marine bacteria may differ in their ability to adapt to changing ocean habitats.
海洋微生物生态学中的一个基本问题是微生物如何适应海洋环境。尽管数量上占优势的种群通常被认为更成功，但较高的种群大小（Nc）并不直接等同于更强的适应能力。相反，有效种群大小（Ne）决定了有害和有利突变的命运，因此是确定种群适应潜力的关键参数。在 SAR11 和 Roseobacter 两个谱系的情况下，它们是海洋表面水中两种丰富的异养细菌，具有不同的生活史策略，基于培养的种群调查表明，SAR11 的 Nc 大于 Roseobacters。为了确定相对 Ne，我们比较了这些分类群最近分化的谱系中非同义替换率与同义替换率（ω）的比值。与 SAR11 亚群相比，几个 Roseobacter 亚群的 ω 值较低，表明这些情况下 Ne 较大。与 Nc 较大的非典型基础 Roseobacter 谱系相比，大多数 Roseobacter 谱系的 ω 值也较小。这一发现为我们提供了关于两个重要海洋细菌谱系中 Ne 变异性的深入了解，并为考虑异养海洋细菌在适应不断变化的海洋生境方面的能力差异提供了进化背景。
