EXTRACTION OF METHANE-OXIDIZING BACTERIA FROM SOIL PARTICLES

We present a method for extraction of active methane (CH4)-oxidizing b acteria from soil samples. The method is based on physical dispersion of bacteria from the soil particles followed by separation of bacteria and soil particles by floatation in the density media Nycodenz or Per coll. Separation on Nycodenz produced very pure bacterial suspensions while separation on Percoll produced rather impure suspensions. Howeve r, more than 60% of the methane-oxidizing activity was irreversibly in hibited in the procedure using Nycodenz compared to less than 10% irre versible inhibition when Percoll was employed. The bacterial suspensio ns extracted from soil can be used to study the physiology and ecology of soil bacteria that oxidize methane at atmospheric concentrations. Our data indicated that these bacteria are extremely difficult to disl odge from particles compared to the majority of bacteria in soil. Tent atively, we interpret the strong attachment to long residence time (i. e. slow turnover) of the methane-oxidizing bacteria. A slow turnover/g rowth rate would explain why soil disturbances, like cultivation, have a long lasting effect on the oxidation of atmospheric methane in soil .