GROWTH OF METHANOTROPHS IN METHANE AND OXYGEN COUNTER GRADIENTS

A gel-stabilized system with counter gradients of CH4 and O-2 was used to grow methanotrophs from wetland, agricultural and forest soils and lake sediment. Columns of semi-solid nitrate- or ammonium-mineral salts medium were continuously flushed at opposite ends with CH4 and O-2 to create opposing concentration gradients of the two gases. Methanotrophs grew from all samples except forest soil, and were visible as thin bands after 5 to 15 days of incubation. The position of growth was CH4 and O-2 concentration-dependent and occurred at the point of maximum possible CH4 oxidation, where both substrates were completely consumed. Evidence was obtained for denitrification and nitrification activities concomitant with CH4 oxidation. This approach may be useful to isolate methanotrophs with different CH4 and O-2 requirements and to study their interactions with other groups of bacteria in nature.