Oxygen sensitivity of methanogenic bacteria

Exponentially growing cells of five methanogenic bacteria were plated on solid media with efficiencies greater than 80%. This permitted the determination of the oxygen sensitivity of these strains under standardized conditions involving the exposure of suspensions of starved cells in non-reduced buffer to air. The death curves of Methanobacterium thermoautotrophicum, Methanobrevibacter arboriphilus and Methanosarcina barkeri were biphasic. Exposures to air for up to 30 h were without effect on the number of colony forming units whereas longer periods of contact with oxygen led to a rapid decrease in viability. In Methanococcus voltae and Methanococcus vannielii the number of surviving cells upon exposure to air dropped exponentially without lag leading to 99% kill within 10 h.