Possible energy sources for chemoautotrophic prokaryotes symbiotic with invertebrates from a Norwegian fjord

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Abstract
In Ypsesund, a marine inlet near Bergen, Norway, the sediment at 33 m contains several invertebrate species that obtain most of their nourishment from endosymbiotic chemoautotrophic prokaryotes. The pogono-phore Siboglinum fiordicum and the bivalve Lucinoma borealis penetrate 25 cm into the sediment, while the bivalves Myrtea spinifera and Thyasira flexuosa live in the top 8 cm. Concentrations of amino acids and possible energy sources for chemoautotrophy (hydrogen, methane, carbon monoxide, formate, ammonia, nitrite and sulphides) were measured at 5 cm intervals in the 0–70 cm layer of sediment. Within the 0–25 cm layer only ammonia and acid-labile sulphide were found in appreciable concentrations. The concentrations of methane, hydrogen, carbon monoxide and nitrite appear to be too low to provide an adequate energy input for the symbiotic bacteria. Extracts of prokaryote-containing tissues from the invertebrates show activity of enzymes concerned in the oxidation of sulphur. It is probable that reduced sulphur compounds are the energy source for the endosymbionts in these animals. The ways in which particulate sulphur species could be exploited are examined. S. fiordicum was found to contain 2.5 mM β-aminoglutaric acid. This compound might be involved in the transfer of fixed carbon from prokaryote to host.