海底是一个广阔的栖息地,支持对地球化学循环具有全球规模影响的微生物。居住在海底的许多地方性微生物群落由生长受限条件下的小种群组成。对于小人口来说,随机进化事件对种内种群动态和等位基因频率有很大影响。这些条件与大多数微生物在表面环境中所经历的条件根本不同,尚不清楚小的种群规模和生长限制条件如何影响地下的进化和种群结构。使用2年,高分辨率环境时间序列,我们研究了来自寒冷的微生物种群的动态,从海底遗址北池塘收集的含氧地壳流体,位于大西洋中脊附近。我们的结果揭示了总体丰度的快速变化,等位基因频率,以及观察到的时间点的菌株丰度,具有共存谱系之间同源重组的证据。我们表明,海底含水层是一个动态的栖息地,它承载着经常分散在地壳流体中的微生物种群,使微生物种群之间的基因流动和重组。北池塘微生物种群动态的动态性和随机性表明,这些力量是广阔海底栖息地微生物种群进化的重要驱动因素。重要性寒冷,海洋海底是一个研究不足的栖息地,很难进入,但对全球生物地球化学循环很重要,与地球表面的微生物栖息地相比截然不同。我们对微生物进化和种群动态的理解在很大程度上是通过对生活在地表栖息地中的微生物的研究来塑造的,这些微生物可以容纳比在地下经常观察到的微生物生物量多10到1000倍的微生物。这项研究提供了一个观察低生物量内种群动态的机会,生长受限的环境,并揭示了海底微生物种群受选择压力和基因扫描变化的影响。此外,从含水层内其他地方分散的菌株之间的重组对微生物种群的进化具有重要影响。地球上的大部分微生物都存在于生长受限的条件下,海底提供了一个自然实验室来探索生命如何在这样的环境中进化。
The
subseafloor is a vast habitat that supports microorganisms that have a global scale impact on geochemical cycles. Many of the endemic microbial communities inhabiting the
subseafloor consist of small populations under growth-limited conditions. For small populations, stochastic evolutionary events can have large impacts on intraspecific population dynamics and allele frequencies. These conditions are fundamentally different from those experienced by most microorganisms in surface environments, and it is unknown how small population sizes and growth-limiting conditions influence evolution and population structure in the subsurface. Using a 2-year, high-resolution environmental time series, we examine the dynamics of microbial populations from cold, oxic crustal fluids collected from the subseafloor site North Pond, located near the mid-Atlantic ridge. Our results reveal rapid shifts in overall abundance, allele frequency, and strain abundance across the time points observed, with evidence for homologous recombination between coexisting lineages. We show that the
subseafloor aquifer is a dynamic habitat that hosts microbial metapopulations that disperse frequently through the crustal fluids, enabling gene flow and recombination between microbial populations. The dynamism and stochasticity of microbial population dynamics in North Pond suggest that these forces are important drivers in the evolution of microbial populations in the vast subseafloor habitat. IMPORTANCE The cold, oxic
subseafloor is an understudied habitat that is difficult to access, yet important to global biogeochemical cycles and starkly different compared to microbial habitats on the surface of the Earth. Our understanding of microbial evolution and population dynamics is largely molded by studies of microbes living in surface habitats that can host 10 to 1,000 times more microbial biomass than is frequently observed in the subsurface. This study provides an opportunity to observe population dynamics within a low biomass, growth-limited environment and reveals that microbial populations in the subseafloor are influenced by changes in selection pressure and gene sweeps. In addition, recombination between strains that have dispersed from elsewhere within the aquifer has an important impact on the evolution of microbial populations. Much of the microbial life on the planet exists under growth-limited conditions, and the
subseafloor provides a natural laboratory to explore how life evolves in such environments.