Data from: High gut microbiota diversity provides lower resistance against infection by an intestinal parasite in bumblebees

The microbiome, especially the gut flora, is known to affect the interaction between parasites and their hosts. In this context, a parasitic infection can be viewed as an invasion into the pre-existing microbial ecological community. Hence, in addition to the intrinsic defense mechanisms of the host itself, infection success depends on the colonization resistance of the microbiota. In the bumblebee, Bombus terrestris, the microbiota provides resistance to the intestinal parasite, Crithidia bombi, yet which properties actually provide protection remains largely unknown. Here, we show that the community structure of the gut microbiota - in terms of bacterial operational taxonomic units (OTUs) of 16S rRNA gene sequences - prior to parasite exposure can be informative of the eventual infection outcome. Specifically, higher microbiota OTU diversity and evenness are associated with less resistance. However, the microbial community structure does not differ between infected and non-infected individuals, or between infected individuals of varying susceptibility. This suggests that parasite infection success depends on microbiota composition but subsequent changes occur, although the exact alteration that occur remain elusive. In fact, the bumblebee microbiota is surprisingly unaffected by parasite exposure and infection. Rather, the microbiota-host interactions prior to parasite exposure seems a key mechanism regulating resistance to infection.

微生物组（microbiome），尤其是肠道菌群（gut flora），已知会影响寄生虫与其宿主之间的相互作用。在此背景下，寄生虫感染可被视为对宿主预先存在的微生物生态群落的入侵。因此，除宿主自身的固有防御机制外，感染能否成功还取决于菌群的定殖抗性（colonization resistance）。在地熊蜂（Bombus terrestris）中，微生物组可帮助其抵御肠道寄生虫熊蜂短膜虫（Crithidia bombi），但究竟是哪些菌群特性发挥了保护作用，目前仍未被充分阐明。本研究表明，在寄生虫暴露前，肠道微生物组的群落结构——以基于16S rRNA基因序列的细菌操作分类单元（operational taxonomic units, OTUs）来表征——可预示最终的感染结局。具体而言，菌群OTU多样性和均匀度越高，宿主的抵御能力反而越弱。然而，受感染个体与未受感染个体之间，或是不同易感性的受感染个体之间，其微生物群落结构并无显著差异。这表明寄生虫感染的成功与否取决于菌群组成，但感染后菌群会发生后续变化，尽管具体的改变机制仍不明确。事实上，熊蜂的微生物组竟未受寄生虫暴露与感染的显著影响。相反，寄生虫暴露前的菌群-宿主相互作用，似乎是调控宿主抗感染能力的关键机制。