Effect of oxygen on liquid holding recovery of Bacteroides fragilis.

Liquid holding recovery (LHR) in ultraviolet-irradiated Bacteroides fragilis cells occurred under aerobic conditions but was inhibited by anaerobic conditions. The increase in survival after aerobic LHR resulted in an increase in the shoulder regions of the ultraviolet survival curves. Maximum LHR was obtained after holding the cells for 2 to 3 h. LHR was temperature dependent, and in stationary-phase cells LHR was independent of nutrients. Higher levels of LHR occurred in exponential-phase cells than in stationary-phase cells, and LHR was affected by nutrients in exponential-phase cells. Sublethal concentrations of caffeine and acriflavine inhibited LHR. In addition to LHR, minimal medium recovery also occurred in the concentration of [3H]thymine-containing dimers in the acid-insoluble fraction of the cells. A corresponding increase in [3H]thymine-containing dimers was observed in the acid-soluble fraction after LHR. Although a small proportion of irradiated cells produced filaments, this phenomenon was not directly related to LHR in B. fragilis.