A dynamic Campylobacterales epibiont community associated with the bone eating wormOsedax

Osedax, the deep-sea annelid found at sunken whalefalls, is known to host Oceanospirillales bacterial endosymbionts intracellularly in specialized roots, that help it feed exclusively on vertebrate bones. Past studies, however, have also made mention of external bacteria on their trunks. During a 14-year study, we reveal a dynamic, yet persistent, succession of Campylobacterales integrated into the epidermis ofOsedax, that change over time as the whale carcass degrades on the sea floor. The Campylobacterales associated with seven species ofOsedax, which comprise 67% of the bacterial community on the trunk, are initially dominated by the genusArcobacter(at early time points < 24 months), theSulfurospirillumat intermediate stages (~ 50 months), and theSulfurimonasat later stages (>140 months) of whale carcass decomposition. Metagenome analysis of the epibiont metabolic capabilities suggests a transition from heterotrophy to autotrophy along the successional gradient, and differences in their capacity to metabolize oxygen, carbon, nitrogen, and sulfur. Compared to free living relatives, theOsedaxepibionts were highly enriched in transposable elements, implicating genetic exchange on the host surface, and contained numerous secretions systems with eukaryotic-like protein domains, suggesting a long evolutionary history with these enigmatic, yet widely distributed deep-sea worms