PhoB expression levels correlate with cell fitness in continuous competition assays.

<p>(A) Non-fluorescent bacteria population in continuous cultures when competed against WT-<i>yfp</i> (RU1622). A 50∶50 mixture of WT-<i>yfp</i> with indicated strains were grown in continuous cultures. Pi-replete and -deplete conditions were achieved with different Pi concentrations, 300 µM (Hi) and 12 µM (Lo), in the fresh medium supplied through the chemostat inlet. Bacteria population at 24 h was used to evaluate cell fitness under Pi-replete (B) and -deplete (C) conditions. Different PhoB levels were achieved with different IPTG concentrations using the following strains: BW25113 (WT, solid square), RU1631 (Δ<i>phoB</i>, open square), RU1616 (LAC, open circle), RU1617 (KON, open diamond), RU1618 (TRC, open triangle) and RU1619 (KON <i>phoB</i>^D53A, solid diamond). PhoB amount was determined previously from 0.3 OD₆₀₀*ml of cells <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1003927#pgen.1003927-Gao2" target="_blank">[19]</a>. A value of 3 pmol in these cells is estimated to correspond to a PhoB concentration of ∼10 µM. Dotted lines represent linear and lognormal trend lines under respective conditions. The solid line represents the saturating dependence of output PhoB∼P levels on total amount of PhoB measured previously <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1003927#pgen.1003927-Gao2" target="_blank">[19]</a>. The star marks the PhoB∼P level at the autoregulated WT concentration of PhoB. Error bars are SDs and the number of independent experiments is documented in <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1003927#pgen.1003927.s004" target="_blank">Table S1</a>.