Continental-scale variation in seaweed host-associated bacterial communities is a function of host condition, not geography

Interactions between hosts and associated microbial communities can fundamentally shape the development and ecology of 'holobionts', from humans to marine habitat-forming organisms such as seaweeds. In marine systems, planktonic microbial community structure is mainly driven by geography and related environmental factors, but the large-scale drivers of host-associated microbial communities are largely unknown. Using 16S-rRNA gene sequencing, we characterized 260 seaweed-associated bacterial and archaeal communities on the kelp Ecklonia radiata from three biogeographical provinces spanning 10° of latitude and 35° of longitude across the Australian continent. These phylogenetically and taxonomically diverse communities were more strongly and consistently associated with host condition than geographical location or environmental variables, and a 'core' microbial community characteristic of healthy kelps appears to be lost when hosts become stressed. Microbial communities on stressed individuals were more similar to each other among locations than those on healthy hosts. In contrast to biogeographical patterns of planktonic marine microbial communities, host traits emerge as critical determinants of associated microbial community structure of these holobionts, even at a continental scale.

宿主与相关微生物群落之间的互作，可从根本上塑造全息生物（holobiont）的发育与生态格局——从人类到大型海藻这类海洋造境生物均属此类。在海洋生态系统中，浮游微生物群落结构主要受地理区位与相关环境因子调控，但目前学界对宿主相关微生物群落的大尺度驱动因子仍知之甚少。本研究通过16S核糖体RNA（16S rRNA）基因测序技术，对澳大利亚大陆范围内跨越10个纬度、35个经度的3个生物地理省中的辐射昆布（Ecklonia radiata）上的260个海藻相关细菌与古菌群落进行了表征分析。这些在系统发育与分类学上均具有丰富多样性的群落，与宿主健康状态的关联程度显著强于地理区位与环境变量；且当宿主处于胁迫状态时，健康昆布特有的"核心"微生物群落似乎会出现丢失。处于胁迫状态的宿主其体表微生物群落在不同采样点位间的相似性，高于健康宿主的微生物群落。与海洋浮游微生物群落的生物地理分布模式截然不同，即便在大陆尺度下，宿主特征仍是这类全息生物相关微生物群落结构的关键决定因素。