OprB1 protein was not Blasticidin S detected in cells without IPTG-induction (not shown). Unmasked β-galactosidase activity assay demonstrated that overexpression of OprB1 caused the lysis of the colR mutant also on the gluconate medium (Figure 4C), which confirms the importance of the amount of OprB1 in OM as a major determinant of cell lysis. Furthermore, even the colR-proficient PaWoprB1-tacB1 strain did not tolerate the artificial overexpression of OprB1, revealing a clear lysis phenotype on both carbon sources. This data suggests that OM is highly sensitive to the abundance of OprB1 and obviously the natural

amount of OprB1 induced by glucose is close to the saturating level that the bacterium can tolerate. Figure 4 Effect of the OprB1 overexpression on the profile of outer membrane proteins and cell lysis. click here A and B. SDS-PAGE of outer membrane protein preparations stained with Coomassie Blue. Representative results of the P. putida PaW85 (wt), oprB1-deficient (B1) as well as OprB1-overexpressing Selleckchem MK2206 strains PaWoprB1-tacB1 (B1tacB1) and PaWcolR-oprB1-tacB1 (RB1tacB1) are presented. OM proteins were extracted from 24-hour-old populations of bacteria grown on solid minimal medium with either 0.2% glucose or gluconate. OM proteins presented in panel B have been purified

from the cells which were grown in the presence of 0.5 mM IPTG. Plus (+) marks above the lanes designate a particular carbon source added to the growth medium. Arrow indicates location of OprB1. C. Quantification of cell lysis by the unmasked β-galactosidase assay. Bacteria were grown for 24 hours on solid 0.2% glucose (glc) or 0.2% gluconate (gn) minimal medium containing 1 mM phenol (+phe). For Carnitine dehydrogenase the induction of OprB1 0.5 mM IPTG was used. Data (mean ± standard deviation) of at least three independent determinations are presented. The degree of lysis of the colR mutant depends on the location of cells in the solid medium population and on the glucose concentration in the medium Two remarkable features of the

glucose-specific cell lysis of the colR-deficient strain are that it can be observed only on solid medium (Figure 1) and that only a fraction of population lyses [25] indicating heterogeneity among the bacteria. Therefore we decided to test the effect of the location of cells in a population on their lysis. For that, the colR-deficient bacteria were grown on agar plates with 0.2% glucose and lysis was analysed in cells withdrawn from two different regions of bacterial lawn on agar plate sectors – the periphery and the centre. Bacteria were streaked as shown in Figure 5A to enhance the build-up of nutrient gradients. Unmasked β-galactosidase activity measured at 24, 48 and 72 hours of growth clearly indicated that at every time-point the lysis of colR mutant was always significantly higher among peripheral cells of the bacterial lawn compared to the central subpopulation (Figure 5B).