Fig 6.

Expression of RpoS or Dps enables wild-type UTI89 to survive low-pH stress at levels similar to those of the ΔcyaA and Δcrp mutants. After reaching mid-logarithmic growth phase in LB broth, UTI89 and the UTI89ΔcyaA, UTI89Δcrp, UTI89Δdps, UTI89ΔrpoS, UTI89ΔcrpΔdps, and UTI89ΔcrpΔrpoS mutants (± pRR48, pdps, and prpoS, as indicated) were exposed to acid (pH 3.5) stress for 30 min. Following washes in PBS, numbers of surviving bacteria were determined by dilution plating. Plasmid-containing strains were grown in the presence of 0.5 mM IPTG prior to challenge with pH stress. Data are expressed as the means ± standard deviations of three independent experiments. P values of <0.05 are indicated by one asterisk (*) for comparison with UTI89 and by two asterisks (**) for comparison with UTI89/pRR48, as determined by two-tailed unpaired t tests.