The bosR::kanR mutant, JH300, displays a delayed growth phenotype relative to the parental, ML23 under microaerobic and anaerobic conditions. Independent cultures were grown in triplicate, cell densities averaged and standard error indicated by bars. A. ML23 (dark squares) and JH300 (open circles) were grown under microaerobic conditions (3.48 ppm dissolved O2, 1% CO2). B. ML23 (dark squares) and JH300 (open circles) were grown under anaerobic conditions (0.087 ppm dissolved O2, 5% CO2). Asterisks indicate significant differences in cell density for a given day (P < 0.001).