Discovery of a Novel Symbiotic Lineage Associated with a Hematophagous Leech from the Genus

Importance: Obligate symbiotic associations with a nutritional base have likely evolved more than once in strict blood-feeding leeches. Unlike those symbioses found in hematophagous arthropods, the nature, identity, and evolutionary history of these remains poorly studied. In this work, we further explored obligate nutritional associations between leeches and their microbial symbionts, which led to the unexpected discovery of a novel symbiosis with a member of the genus. When compared to , an obligate nutritional symbiont of other leeches, this novel bacterial symbiont shows convergent retention of the metabolic pathways involved in B vitamin biosynthesis. Moreover, the genomic characteristics of this symbiont suggest a more recent association than that of and . We conclude that the once-thought stable associations between blood-feeding Glossiphoniidae and their symbionts (i.e., one bacteriome structure, one symbiont lineage) can break down, mirroring symbiont turnover observed in various arthropod lineages.