Survival patterns of different exonuclease mutants competing with wild-type parental strains when cocultured in LB broth. Cultures were continuously incubated for 14 days at 37°C with aeration. Each competition was performed in triplicate; different symbols represent different competition pairs. Strains contain a null mutation for exonuclease I (A), RecJ exonuclease (B), exonuclease VII (C), or exonuclease X (D). Mutant and wild-type strains are represented by filled and open symbols, respectively. Asterisks indicate no detectable counts (the limit of detection is <1,000 CFU/ml).