Methylotrophic and autotrophic bacteria isolated from lucinid and thyasirid bivalves containing symbiotic bacteria in their gills

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Abstract
Bacteria have been isolated into pure culture from the gills ofLucinoma borealis, Myrtea spinifera, Thyasira flexuosaandT. sarsicollected from several British and Scandinavian coastal sediments. It is proposed that these bacteria are symbiotic with the animals. The bacteria were either autotrophs, obtaining energy from oxidation of inorganic sulphur compounds, or methylotrophs using methanol or methylamine as the source of carbon and energy. The latter could also oxidize thiosulphate to tetrathionate and precipitate elemental sulphur. The pure cultures have been characterised in some detail, showing that (1) their DNA base composition falls in the range 47–58% guanine + cytosine; (2) although all grow well at the natural environment temperatures of 8–15°C, their optima lie between 30 and 35°C; (3) all produce copious amounts of extracellular slime when grown at low temperatures; (4) the autotrophic isolate is facultatively heterotrophic, containing a repressible ribulose bisphosphate carboxylase, and excreting up to 30% of its carbon dioxide fixation into the culture medium; (5) the methylotrophs include some containing high activities of hexulose phosphate synthase for assimilation of formaldehyde by the ribulose monophosphate cycle; others may have novel assimilatory metabolism. The possibility is discussed that environmental factors may determine whether a methylotroph-animal or autotroph-animal symbiosis is established rather than the symbiont type being an invariable species-specific character.