FIG. 7.
Effect of nrdA mutation on growth of B. fragilis. (A) Growth curves of strains IB267 (nrdA) and IB271 (control, W+) during exposure to O2. At time zero, mid-logarithmic-phase cultures were exposed to O2 by being shaken in air at 37°C or were maintained under anaerobic conditions in stoppered tubes in the anaerobic chamber. Growth was monitored by measurement of A550 at the specified intervals. (B) Recovery curve of B. fragilis IB267 and IB271 following exposure to O2 for 48 h in BHIS. At time zero, approximately 107 viable, stressed bacteria were added to 10 ml of prereduced BHIS. The culture was incubated anaerobically at 37°C, and the A550 was monitored at 1-h intervals until growth was observed. The data presented are representative of the results from three independent experiments.