FIG. 4.

PCR amplification of phlA gene in P. fluorescens CHA0 (cells from 1-day-old cultures; used at 7.7 log CFU/ml) following the addition (50:50 [vol/vol]) of cell samples obtained after incubation for 1 day at pH 4 (2.09 ± 0.36 log CFU/ml). Lanes: M, 100-bp ladder; 1, pH 7 cells; 2, pH 4 cells; 3, pH 7 cells and pH 4 cells mixed before lysis; 4, pH 7 cells and pH 4 cells mixed after lysis; 5, pH 4 cells and pH 7 buffer mixed before lysis; 6, pH 7 cells and pH 4 buffer mixed before lysis; 7, pH 7 buffer; 8, pH 4 buffer; 9, water blank. Identical results were obtained when PCR was performed after DNA purification of pH 7 and pH 4 samples (cell lysates) by direct ethanol precipitation (16) or phenol-chloroform-isoamyl alcohol extraction (followed by precipitation with 1 volume of 2 M NaCl and 2 volumes of ice-cold 95% ethanol) instead of with cell lysates directly (data not shown). Each treatment was replicated at least four times.