Abstract：
The spatiotemporal distribution of MASTs (MArine STramenopiles), mostly affiliated with heterotrophic protists, and their interactions with Synechococcales were investigated in an anthropogenically polluted bay of the East Sea using 18S rRNA and 16S rRNA gene sequences. The bay was characterized by strong stratification between the surface and bottom layers and cold and nutrient-rich water intrusion in summer, whereas the bay water was well mixed in winter. MAST-3, MAST-6, MAST-7, and MAST-9 were the major MAST clades, whereas the dominance of MAST-9 declined from >80 % in summer to <10 % in winter and the diversity of MAST communities increased in winter. Co-occurrence network analysis via the sparse partial least squares revealed that MAST-3 had a Synechococcales-specific interaction during the study periods but prey-specific interactions with other MAST clades were not detected. Temperature and salinity markedly influenced the relative abundance of major MAST clades. The relative abundance of MAST-3 increased at temperatures above 20 °C and salinities above 33 ‰, however, the abundance of MAST-9 decreased under the same conditions. Analysis of the metabolic functions of cyanobacteria using the FAPROTAX (Functional Annotation of Prokaryotic Taxa) indicated that the response of photosynthetic cyanobacteria to NH4+ and PO43- was significant in summer but these functions were not tightly coupled with the abundance of Synechococcales. Similarly, strong associations of MAST-3 with high temperature/salinity and Synechococcales were indicative of coupled cascading during bottom-up processes. However, other major MAST clades were likely decoupled with Synechococcales and environmental conditions in which cyanobacteria can thrive. Therefore, our results demonstrated that MAST communities can couple or decouple with environmental variables and potential prey depending on MAST clades. Collectively, our findings provide novel insights into the role of MAST communities in microbial food webs in eutrophic coastal waters.
摘要：
MAST（MAST）的时空分布，主要与异养原生生物有联系，在东海人为污染的海湾中，使用18SrRNA和16SrRNA基因序列研究了它们与Synechococcales的相互作用。海湾的特点是表层和底层之间分层强烈，夏季寒冷和营养丰富的水入侵，而海湾的水在冬天混合得很好。MAST-3，MAST-6，MAST-7和MAST-9是主要的MAST进化枝，而MAST-9的优势从夏季的>80％下降到冬季的<10％，而MAST群落的多样性在冬季增加。通过稀疏偏最小二乘法进行的共现网络分析显示，在研究期间，MAST-3具有协同球菌特异性相互作用，但未检测到与其他MAST进化枝的猎物特异性相互作用。温度和盐度显着影响主要MAST进化枝的相对丰度。MAST-3的相对丰度在温度高于20℃和盐度高于33‰时增加，然而,在相同条件下，MAST-9的丰度降低。使用FAPROTAX（原核类群的功能注释）对蓝藻的代谢功能进行分析，表明光合蓝藻对NH4和PO43-的响应在夏季是显着的，但这些功能与大量的蓝藻并没有紧密耦合。同样，MAST-3与高温/盐度和Synechococales的强烈关联表明在自下而上的过程中存在级联。然而,其他主要的MAST进化枝可能与蓝细菌繁殖的环境条件以及蓝细菌的繁殖条件脱钩。因此,我们的结果表明，根据MAST进化枝，MAST群落可以与环境变量和潜在猎物配对或解耦。总的来说，我们的发现为富营养化沿海水域微生物食物网中MAST群落的作用提供了新的见解。
