Distribution of Methanotrophic Bacteria in the Coastal Marine Sediments

Abstract

Methanotrophic bacteria attract attention from the viewpoints of biology, geochemistry and bioremediation. However, the ecology of marine methanotrophs is not well known in spite of their possible important role in the environment, 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 and released carbon dioxide. Under TEM observation the cultures contained bacteria with the stacked intracytoplasmic membrane system, which is characteristic of group I methanotrophic bacteria. MPN method with tentative growth confirmation by TEM observation was applied to enumerate methanotrophic bacteria in the sediments from Otsuchi Bay, Tokyo Bay, and Aburatusbo Inlet. The count had positive correlation with the viable count of heterotrophic bacteria. Vertical distributions in sediment samples at two stations in Tokyo Bay showed a high count of methanotrophic bacteria and low methane concentration in shallow sediment, which suggested the methane profile was caused by the activity of methanotrophs. The highest count of methanotrophic bacteria was 2400 MPN in 1ml of the marine sediment.