Endosymbiotic bacterial species that manipulate host biology, reproduction and mitochondrial genetic diversity have been identified in many metazoans, especially terrestrial arthropods. Until now, the hypothesis that Wolbachia or other bacterial endosymbiont might be absent in mollusks has remained unexplored. We present here preliminary data on bacterial communities in a freshwater mussel Unio crassus—species with doubly uniparental inheritance of mtDNA (DUI). Next generation sequencing of 16S rRNA bacterial gene fragment allowed to identify endosymbiotic Cardinium and sequences that were classified to the order Rickettsiales. Finally, we discovered Wolbachia and confirmed Cardinium infection of Unio crassus using bacterial species-specific primers. Discovering Wolbachia and Cardinium infections in Unio crassus opens new opportunities of further investigations in the second largest animal phylum on Earth, very diversified phylogenetically, widespread geographically and inhabiting many environs, including freshwater, inhabited by the most threatened molluscan species. Considering the problems caused by endosymbionts identified in arthropods, the presence of endosymbiotic factor implies possibility of their influence on taxonomy of threatened unionids, on the results of studies of genetic diversity and proper conservation planning.

在许多后生动物，尤其是陆生节肢动物中，已经发现了操纵宿主生物学，繁殖和线粒体遗传多样性的内共生细菌物种。直到现在，软体动物中可能不存在沃尔巴氏菌或其他细菌内共生体的假设仍未得到证实。我们在此介绍淡水贻贝Unio crasus中的细菌群落的初步数据，这些物种具有mtDNA（DUI）的双单亲遗传。通过16S rRNA细菌基因片段的下一代测序，可以鉴定共生内生菌素Cardinium以及被分类为立克次体的序列。最后，我们发现了Wolbachia，并确认了Cardinium感染使用细菌物种特异的引物对南方紫荆。在Unio crassus中发现Wolbachia和Cardinium感染，为进一步研究地球上第二大动物门提供了新的机会，该系统在系统发育上非常多样化，在地理上广泛分布，并居住在许多环境中，包括淡水，它们是最受威胁的软体动物的栖息地。考虑到节肢动物中发现的共生共生菌引起的问题，共生共生因子的存在暗示了它们对受威胁的工会体的分类学，遗传多样性研究结果和适当的保护计划的影响。