Phylogenetic characterization and biomass estimation of bacterial endosymbionts associated with invertebrates dwelling in chemosynthetic communities of hydrothermal vent and cold seep fields

Abstract

Molecular phylogenetics for endosymbiotic bacteria recovered from vestimentiferan tubeworm Lamellibrachia satsuma from Kagoshima Bay, vesicomyid clam Calyptogena laubieri from the Nankai Trough and mytilid mussel Bathymodiolus sp. from the Mariana Back-arc Basin, were examined by PCR-aided 16S rDNA cloning and sequencing, and quinone profiling. The 16SrRNA clones of the endosymbionts from the 3 organisms fall within γ-Proteobacteria and showed distinct lines of descent specific to their respective host. The 16S rRNA gene phylogeny confirms the host-endosymbiont specificity in the co-evolutionary process. Ubiquinones with 9 isoprene units (Q-9) or Q-10 were found as the major quinones in all test tissues of the host. Larger amounts of Q-8 were detectable only in those host body parts (gill or trophosome) harboring the endosymbiotic bacteria. These observations suggest that Q-8 is the major quinone of the endosymbionts. Based on the bacterial quinone concentration, the population densities of the bacteria present were estimated to be 1010 to 1011 cells g-1 wet wt of host tissue. The quantitative determination of quinones may provide information about physiological activity of the chemosynthetic communities as well as their biomass production.