Cell population structure by flow cytometry analysis. P. putida wild-type (wt), colR-deficient (colR), ttgC-deficient (ttgC) and colRttgC double mutant (colRttgC) strains were grown for 24 h on glucose (A) or gluconate (B) minimal plates. Concentration of phenol (phe) in growth medium (either 3 mM, 6 mM or 8 mM) is indicated below the bars. Cells were stained with PI and SYTO9 and analysed by flow cytometry. Relative proportions of seven subpopulations (as indicated in Figure 4) are shown. Data (mean ± standard deviation) of at least three independent determinations are presented.