Phylogeny and diversity of deep-sea chemosynthetic symbionts and their host animals

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The genes encoding key enzymes for chemosynthesis and methanotrophy, RuBisCO and pmoA, respectively, were first endosymbiotically localized in parallel with symbiont-specific 16S rRNA genes in the tissues of pogonophorans and bivalves inhabiting hydrothermal vents and methane seeps by in situ hybridization (ISH). The ISH revealed that :(1) pogonophoran symbionts are sulfur-oxidizing chemoautotrophs or methanotrophs ;(2) pogonophoran hosts may harbor more than one symbiont species ; and(3) bivalve hosts may harbor both sulfur-oxidizing chemoautotrophs and methanotrophs simultaneously.Other major findings relevant to chemoautotrophy, methanotrophy and related redox processes are :(4) some euryhaline halophiles that have been regarded as heterotrophs are chemosutotrophs ;(5) euryhaline halophiles occur in hydrothermal vents, methane seeps and other extreme environments ; and(6) some halophiles accelerate precipitation of authigenic carbonate rocks in methane seeps.