Data_Sheet_1_Convergence of biofilm successional trajectories initiated during contrasting seasons.docx

Biofilm communities play a major role in explaining the temporal variation of biogeochemical conditions in freshwater ecosystems, and yet we know little about how these complex microbial communities change over time (aka succession), and from different initial conditions, in comparison to other stream communities. This has resulted in limited knowledge on how biofilm community structure and microbial colonization vary over relevant time scales to become mature biofilms capable of significant alteration of the freshwater environment in which they live. Here, we monitored successional trajectories of biofilm communities from summer and winter in a headwater stream and evaluated their structural state over time by DNA high-throughput sequencing. Significant differences in biofilm composition were observed when microbial colonization started in the summer vs. winter seasons, with higher percentage of algae (Bacillariophyta) and Bacteroidetes in winter-initiated samples but higher abundance of Proteobacteria (e.g., Rhizobiales, Rhodobacterales, Sphingomonadales, and Burkholderiales), Actinobacteria, and Chloroflexi in summer-initiated samples. Interestingly, results showed that despite seasonal effects on early biofilm succession, biofilm community structures converged after 70 days, suggesting the existence of a stable, mature community in the stream that is independent of the environmental conditions during biofilm colonization. Overall, our results show that algae are important in the early development of biofilm communities during winter, while heterotrophic bacteria play a more critical role during summer colonization and development of biofilms.

生物膜群落对阐明淡水生态系统中生物地球化学条件的时空变化起着至关重要的作用，然而，我们对这些复杂的微生物群落如何随时间（即演替）以及与不同初始条件相比，如何与其他溪流群落发生变化所知甚少。这导致了我们对生物膜群落结构以及微生物殖民化在相关时间尺度上如何变化以形成能够显著改变其生活淡水环境的成熟生物膜的了解有限。在本研究中，我们监测了源头溪流中夏季和冬季生物膜群落演替的轨迹，并通过DNA高通量测序评估了其结构状态随时间的变化。观察到，与夏季相比，冬季开始的微生物殖民化过程中生物膜组成存在显著差异，冬季启动的样本中藻类（如硅藻门）和拟杆菌门的百分比更高，而夏季启动的样本中变形菌门（例如，豆科菌目、红螺菌目、鞘氨醇单胞菌目和伯克霍尔德菌目）、放线菌门和绿弯菌门的丰度更高。有趣的是，结果显示，尽管季节性效应对早期生物膜演替有影响，但生物膜群落结构在70天后趋于一致，这表明存在一个稳定成熟的群落，该群落不受生物膜殖民化期间环境条件的影响。总体而言，我们的研究结果表明，在冬季生物膜群落早期发展中藻类起着重要作用，而在夏季殖民化和生物膜发展中，异养细菌则扮演着更为关键的角色。