热胁迫驱动鹿角杯形珊瑚中与特异虫黄藻系群相关的细菌群落演替

Heat stress drives shift in bacterial communities associated with distinct Symbiodiniaceae clades in the coral Pocillopora damicornis

摘要:

目的 探究细菌与虫黄藻之间的互作关系，以及该关系在珊瑚高温胁迫适应中的作用。方法 以共生不同系群虫黄藻的鹿角杯形珊瑚(Pocillopora damicornis)为研究对象，通过室内模拟高温胁迫实验，结合核糖体16S rRNA基因扩增子测序解析珊瑚内共生细菌群落在高温胁迫下的动态演替情况。结果 共生C系群(Cladocopium spp.)与D系群(Durusdinium spp.)虫黄藻的鹿角杯形珊瑚(分别简称PdC与PdD全共生体)的细菌多样性均呈现胁迫初期短暂升高、胁迫后期显著下降的趋势。与PdD相比，胁迫后期PdC的细菌群落组成变化更大，网络结构的稳定性与复杂性随胁迫时间延长逐渐减弱。二者在纲水平上也表现出不同的细菌丰度变化，胁迫后期α-变形菌纲的相对丰度在两组中均增加，而蓝细菌纲的相对丰度则表现为在PdC中上升、在PdD中下降的趋势。在高温胁迫后期，PdC中的C系虫黄藻对热敏感，潜在的条件致病菌丰度明显增加；而PdD中的D系虫黄藻具有热耐受性，基于物种组成与丰度预测，某些共生细菌可能在光合作用、群体感应、钙化作用以及ABC转运等过程中发挥作用。结论 本研究揭示了不同类型虫黄藻与细菌互作对鹿角杯形珊瑚响应高温胁迫的差异调控作用。PdC珊瑚共生体出现白化现象，或许与C系群虫黄藻对热敏感以及潜在条件致病菌的入侵程度有关；而PdD珊瑚共生体具有高温耐受性，可能源于耐热的D系群虫黄藻及某些益生菌所提供的辅助代谢功能(如光合、钙化、群体感应等)。这种藻菌互作模式为理解珊瑚热白化的微生物学机制提供了重要依据，对全球气候变化背景下的珊瑚礁修复具有重要的参考意义。

Abstract:

Objective To investigate the interactions between coral-associated Symbiodiniaceae and bacteria in mediating heat stress adaptation of corals.Methods Using Pocillopora damicornis harbouring distinct Symbiodiniaceae clades, we performed a laboratory-controlled heat stress simulation experiment to examine the dynamics of symbiotic bacterial community shifts via 16S rRNA gene amplicon sequencing.Results Bacterial alpha diversity exhibited a transient increase during the initial stress, followed by a significant decrease under prolonged stress, in P. damicornis harbouring clade C (Cladocopium spp.) or clade D (Durusdinium spp.) algal symbionts (i.e., PdC versus PdD holobionts). Compared with PdD, PdC demonstrated enhanced bacterial community shifts, alongside progressively diminished network stability and complexity with prolonged heat stress. Analysis of bacterial abundance at the class level revealed divergent trajectories of the two holobionts, with the abundance of Alphaproteobacteria increasing in both PdC and PdD, whereas that of Cyanobacteriota increasing in PdC but decreasing in PdD over the course of the experiment. During the later stage of heat stress, Cladocopium spp. in PdC showed increased sensitivity, coinciding with the enrichment of potentially opportunistic pathogens, whereas Durusdinium spp. in PdD were thermotolerant, coinciding with elevated abundance of bacteria possibly involved in photosynthesis, quorum sensing, calcification, and ABC transport.Conclusion These findings suggest that different clades of Symbiodiniaceae might interact with bacteria to differentially regulate the P. damicornis response to heat stress. Thermal sensitive Cladocopium spp., combined with the proliferation of potential opportunistic pathogens, may exacerbate the risk of thermal bleaching in PdC, whereas resilience could be strengthened in PdD via thermotolerant Durusdinium spp. coordinating with beneficial bacteria with supportive metabolic potential (e.g., photosynthesis, calcification, and quorum sensing). This algal-bacterial interaction mode provides critical insights into the microbially-mediated thermal bleaching mechanisms and an important reference for the practice of reef restoration in the context of global climate change.