SENSITIVITY OF METHANOGENIC BACTERIA FROM PADDY SOIL TO OXYGEN AND DESICCATION

The effects of combinations of desiccation and exposure to O2 were studied in pure cultures of Methanosarcina barkeri Strain Fusaro and in a new Methanosarcina strain and a new Methanobacterium strain which were both isolated from dry oxic paddy soil. Incubation of bacterial suspensions under air for 200 min resulted in a decreased potential to produce CH4, but not in a decreased viability. The inhibitory effect of O2 slightly increased with increased salt concentration. Desiccation of bacterial suspensions under N2 resulted in reduction of viability to 10% and of potential CH4 production to 0.6%. Desiccation of bacterial suspensions under air resulted in a larger decrease of both viability (0.5%) and potential CH4 production (0.03%). This decrease was smaller at rapid compared to slow desiccation. Survival and potential CH4 production were further inhibited when the suspension was dried in the presence of sand grains or glass beads coated with FeS or FeNH4PO4. However, survival and potential CH4 production increased dramatically in the presence of pyrite (FeS2) grains. Then, as much as 10% of the initial methanogenic population survived oxic desiccation. This relatively good resistance is in agreement with observations that methanogens in rice fields survive the periods when the paddy soil is dry and oxic.