Acid survival of mutant strains.

<p>Single-gene mutants of <i>E. coli</i> K-12 strain W3110 were constructed as described under <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0056796#s2" target="_blank">Methods</a>. Strains defective for <i>gadC</i>, <i>rpoS</i>, <i>cfa</i>, <i>hypF</i>, and <i>fnr</i> were cultured overnight and exposed to pH 2.0 for 2 hours before being diluted 1∶80,000 and 1∶400,000 under anoxic and aerated conditions, respectively. Dilutions were then plated allowing colonies to grow up overnight at 37° C. The number of colonies per plate was log transformed and a ratio of acidic exposure – control (pH 7.0) and a percentage was calculated from that ratio. Extreme acid medium was autoclave sterilized (Light bars); or filter sterilized (dark bars). Error bars indicate SEM (n = 5 or 6). * denotes undetectable colony counts on dilution plates and a corresponding survival of <1%.