Figure 4. l-serine catabolism contributes to P. mirabilis fitness in LB broth.

(A) Wild-type P. mirabilis and indicated serine catabolism mutants were cultured in LB broth at 37°C with aeration in 96-well plates, and growth was assessed by measurement of OD₆₀₀ at 15-minute intervals for 18 hours. Error bars represent mean ± SD from at least 6 technical replicates, and graph is representative of at least 3 independent experiments. (B-D) LB broth was inoculated with a 50:50 mixture of the indicated serine catabolism mutant and wild-type P. mirabilis, and fitness was assessed by calculating a competitive index based on the CFUs of each strain at hourly time points. Where indicated, LB broth was supplemented with 10 mM alanine or pyruvate. Each data point indicates the log₁₀ competitive index for the indicate mutant:WT inoculum from a single culture. Error bars represent the mean ± SD from at least 3 independent experiments, and the dashed line indicates Log₁₀ CI=0 (the expected value if the ratio of mutant:WT is 1:1). *p<0.05 by Wilcoxon signed-rank test, with specific co-challenges indicated by color-coding.