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Abstract

Deep-sea Bathymodiolus mussels and their chemoautotrophic symbionts are
well-studied representatives of mutualistic host-microbe associations.
However, how host-symbiont interactions vary on the molecular level
between related host and symbiont species remains unclear. Therefore, we
compared the host and symbiont metaproteomes of Pacific B. thermophilus,
hosting a thiotrophic symbiont, and Atlantic B. azoricus, containing two
symbionts, a thiotroph and a methanotroph. We identified common
strategies of metabolic support between hosts and symbionts, such as the
oxidation of sulfide by the host, which provides a thiosulfate reservoir
for the thiotrophic symbionts, and a cycling mechanism that could supply
the host with symbiont-derived amino acids. However, expression levels
of these processes differed substantially between both symbioses. Backed
up by genomic comparisons, our results furthermore revealed an
exceptionally large repertoire of attachment-related proteins in the B.
thermophilus symbiont. These findings imply that host-microbe
interactions can be quite variable, even between closely related
systems.