Death rates of obligate anaerobes exposed to oxygen and the effect of media prereduction on cell viability

Stationary-phase cells of Methanospirillum hungatei GP1, Methanobacterium thermoautotrophicum ΔH, Methanobacterium bryantii M.o.H., Fusobacterium sp., Bacteroides fragilis, and Eubacterium limosum were aerated in medium devoid of cysteine – sodium sulfide (cysteine–Na2S) reducing agents to determine the death rates caused by exposure to oxygen. D values (time in minutes required to destroy 90% of the initially viable population) for these anaerobes were 208, 293, 543, 239, 410, and 507 min, respectively. Death was exponential throughout the treatment period for all the anaerobes, except B. fragilis and E. limosum which showed no significant death for the first 2 and 9 h of aeration, respectively. A minimum prereduction period of 6 h inside an anaerobic chamber was required for aerobically poured agar medium containing cysteine–Na2S to achieve maximum viable cell recovery of the nonmethanogens not previously exposed to air. The results also showed that agar medium containing reducing agents, poured anaerob...