Distinct Bacterial Microbiomes in Sexual and Asexual Potamopyrgus antipodarum, a New Zealand Freshwater Snail

Different reproductive strategies and the transition to asexuality can be associated with microbial symbionts. Whether such a link exists within mollusks has never been evaluated. We took the first steps towards addressing this possibility by performing pyrosequencing of bacterial 16S rRNA genes associated with Potamopyrgus antipodarum, a New Zealand freshwater snail. A diverse set of 60 tissue collections from P. antipodarum that were genetically and geographically distinct and either obligately sexual or asexual were included, which allowed us to evaluate whether reproductive mode was associated with a particular bacterial community. 2624 unique operational taxonomic units (OTU, 97% DNA similarity) were detected, which were distributed across ~30 phyla. While alpha diversity metrics varied little among individual samples, significant differences in bacterial community composition and structure were detected between sexual and asexual snails, as well as among snails from different lakes and genetic backgrounds. The mean dissimilarity of the bacterial communities between the sexual and asexual P. antipodarum was 90%, largely driven by the presence of Rickettsiales in sexual snails and Rhodobacter in asexual snails. Our study suggests that there might be a link between reproductive mode and the bacterial microbiome of P. antipodarum, though a causal connection requires additional study.

不同繁殖策略以及向无性繁殖的转变，或与微生物共生体存在关联。目前学界尚未对软体动物（mollusks）中是否存在此类关联开展评估。我们通过对新西兰淡水螺（Potamopyrgus antipodarum）的相关细菌16S rRNA基因进行焦磷酸测序，为验证这一可能性迈出了第一步。本次研究纳入60份来自P. antipodarum的组织样本，这些样本在遗传背景与地理分布上均存在差异，且分别为专性有性繁殖或专性无性繁殖类群，借此我们得以评估繁殖模式是否与特定细菌群落存在关联。共检出2624个独特的操作分类单元（operational taxonomic unit，OTU，DNA相似性阈值为97%），这些单元分属约30个细菌门。尽管单个样本间的α多样性指数（alpha diversity metrics）差异极小，但我们检测到有性与无性繁殖螺类的细菌群落组成及结构存在显著差异，不同湖泊来源及遗传背景的螺类群落也存在显著差异。有性与无性繁殖的P. antipodarum之间的细菌群落平均相异度达90%，这一差异主要由有性螺类中的立克次体目（Rickettsiales）与无性螺类中的红杆菌属（Rhodobacter）的丰度差异主导。本研究表明，P. antipodarum的繁殖模式与其细菌微生物组（microbiome）之间可能存在关联，但二者的因果关系仍需进一步研究验证。