Marine microbial thiotrophic ectosymbioses

Abstract

A high diversity of thiotrophic symbioses is found in sulphide-rich marine habitats, involving several phyla of protists and invertebrates, as well as several subdivisions of the Proteobacteria. Whereas some of the better-known symbioses are highly evolved endosymbioses, the more primitive ectosymbioses are less well known. The sulphur-oxidising chemolithotrophic nature of the bacteria and their nutritive importance to the eukaryote host have been demonstrated for the ciliates Kentrophoros spp. and Zoothamnium niveum, the nematode subfamily Stilbonematinae, and the carid shrimp Rimicaris exoculata. For a number of other regular bacteria-eukaryote associations, such a symbiotic relationship has been hypothesised based on ecological, morphological, physiological or molecular data, but is still inconclusive.