Distribution of methanotrophic bacteria in the coastal marine sediments

Methanotrophic bacteria attract attention from the viewpoints of biology, g eochemistry and bioremediation. However, the ecology of marine methanotroph s is not well known in spite of their possible important role in the enviro nment, partly because they are difficult to cultivate. Enrichment cultures of methanotrophic bacteria were obtained from coastal marine sediment under 1:1 methane and air conditions. The cultures utilized methane and oxygen a nd released carbon dioxide. Under TEM observation the cultures contained ba cteria with the stacked intracytoplasmic membrane system, which is characte ristic of group I methanotrophic bacteria. MPN method with tentative growth confirmation by TEM observation was applied to enumerate methanotrophic ba cteria in the sediments from Otsuchi Bay, Tokyo Bay, and Aburatusbo Inlet. The count had positive correlation with the viable count of heterotrophic b acteria. Vertical distributions in sediment samples at two stations in Toky o Bay showed a high count of methanotrophic bacteria and low methane concen tration in shallow sediment, which suggested the methane profile was caused by the activity of methanotrophs. The highest count of methanotrophic bact eria was 2400 MPN in 1 ml of the marine sediment.