Zheng Xinyi, Guo Xin, Lin Xiaoqing, Huang Lingfeng
Key Laboratory of the Ministry of Education for Coastal and Wetland Ecosystems, College of the Environment and Ecology, Xiamen University, Xiamen, China.
State Key Laboratory of Marine Environmental Science, College of Ocean and Earth Sciences, Fujian Key Laboratory of Marine Carbon Sequestration, Xiamen University, Xiamen, China.
Appl Environ Microbiol. 2025 Jun 26:e0043625. doi: 10.1128/aem.00436-25.
The microbial food web plays a critical role in marine ecosystems, composed of various cell sizes of microbial organisms. Here, high-throughput sequencing of the 16S and 18S rRNA genes was conducted to detect the community structure and distribution patterns of bacterioplankton (0.2 µm-2 µm) and three size fractions of protist communities, i.e., pico-protist (0.2 µm-2 µm), nano-protist (2 µm-20 µm), and micro-protist (20 µm-200 µm), in the euphotic zone of the South China Sea. The trophic mode compositions of protist communities varied significantly across three size fractions, characterized by a substantial prevalence of parasitic pico-protists (40% amplicon sequence variants) and a greater predominance of mixotrophic taxa within nano- and micro-protist communities. Furthermore, we detected stronger vertical stratification of bacterial and pico-protist communities, corresponding to the wider niche breadth of smaller cells and reliance on passive dispersal. Additionally, both bacterial and protist community assemblies were dominated by stochastic processes. The relative contribution of homogeneous selection in nano-protist community assembly was greater compared to other size fractions, probably related to high relative abundance of mixotrophs. In summary, our results suggest that both cell size and trophic mode affect marine microbial community assembly, and that neither the "size-plasticity" hypothesis nor the "size-dispersal" hypothesis fully matched microbial communities. Our analyses are important for a better understanding of the assemblage processes of marine epipelagic microbial communities and how they will respond to global change.IMPORTANCECell size is a key feature that influences microbial biology at both the cellular and community levels. Poorly understood is the extent to which diverse ecological factors influence the assembly of microbial communities of various sizes. Two important hypotheses addressing the mechanisms of biome assembly are "size-plasticity" and "size-dispersal." Here, we investigated epipelagic microbial communities to reveal differences in the ecological functions of various microbial sizes, to explore the association of ecological processes with niche and cell size, and to expand the current understanding of marine microbial community assemblages and their possible responses to future global change.
微生物食物网在海洋生态系统中起着关键作用，它由各种细胞大小的微生物组成。在此，我们对16S和18S rRNA基因进行了高通量测序，以检测南海真光层中浮游细菌（0.2微米至2微米）以及原生生物群落的三个大小级分，即微微型原生生物（0.2微米至2微米）、微型原生生物（2微米至20微米）和小型原生生物（20微米至200微米）的群落结构和分布模式。原生生物群落的营养模式组成在三个大小级分中差异显著，其特征是寄生性微微型原生生物占比很大（40%的扩增子序列变体），而在微型和小型原生生物群落中混合营养类群占主导地位。此外，我们检测到细菌和微微型原生生物群落有更强的垂直分层现象，这与较小细胞更广泛的生态位宽度以及对被动扩散的依赖相对应。另外，细菌和原生生物群落的组装都受随机过程主导。与其他大小级分相比，均匀选择在微型原生生物群落组装中的相对贡献更大，这可能与混合营养生物的高相对丰度有关。总之，我们的结果表明，细胞大小和营养模式都会影响海洋微生物群落的组装，而且“大小可塑性”假说和“大小扩散”假说都不完全符合微生物群落的情况。我们的分析对于更好地理解海洋上层微生物群落的组装过程以及它们对全球变化的响应具有重要意义。重要性细胞大小是在细胞和群落水平上影响微生物生物学的一个关键特征。人们对各种生态因素在多大程度上影响不同大小微生物群落的组装了解甚少。解决生物群落组装机制的两个重要假说是“大小可塑性”和“大小扩散”。在此，我们研究了海洋上层微生物群落，以揭示不同微生物大小的生态功能差异，探索生态过程与生态位和细胞大小的关联，并扩展当前对海洋微生物群落组装及其对未来全球变化可能响应的理解。
