Spirochetes in gastropods from Lake Baikal and North American freshwaters: new multi-family, multi-habitat host records

We describe the first records of spirochetes in the gut of fourteen species of continental gastropods from a range of habitats and representing six families (Amnicolidae, Baicaliidae, Bithyniidae, Pyrgulidae, Lithoglyphidae and Benedictiidae). The bacteria were mainly found in the crystalline style sac, as has been reported in marine bivalves. The surveyed habitats include water bodies in North America and Eurasia, including deep water hydrothermal vent and gas hydrate zones in Lake Baikal. Spirochetes were present both in mature and young snails, but were not detected in embryos before hatching, indicating lateral transfer. The surveyed gastropods range in trophic strategy, including phyto-, detrito- and bacteriophagous grazers and filter feeders. Our results indicate that spirochetes are commensal in the surveyed gastropods with potential limited benefit and no detriment to the host animal. We suggest that the specialized internal habitat of the crystalline style sac in molluscs is likely to reveal unrecognized spirochete diversity that will shed new light on gastropod trophic ecology and spirochete diversity.