Analysis of pH effects on growth. (a) Effect of pH and media on the growth of F. tularensis LVS wild type (wt) and ΔripA strains. The initial pH of BHI and CDM was measured as 7.3 and 6.3 respectively. Cultures were seeded at time zero with 1.12 × 108 CFU/ml. Klett measurements were recorded at the listed times. The growth curves displayed are a representative example of growth under the indicated conditions. F. tularensis growth over time shifts the pH of the media by the secretion of ammonia. The initial pH of the media shifts by < 0.2 pH units by 6 hours and from 0.5 to 1.0 pH units by 24 hours. (b) The growth of F. tularensis LVS (wt), ΔripA, and ΔripA pripA in CDM with a starting pH of 6.5 or 7.5 was measured at 24 hours. The mean OD600 of four replicates is represented with error bars representing ± one standard deviation. The growth of F. tularensis LVS ΔripA was significantly less (P < 0.05) than wild type and the ΔripA pripA strain as tested using a Student's t test.