The TtgABC homologue in Escherichia coli, AcrAB-TolC, is also involved in extrusion of quorum sensing signals and in regulation of population entering into stationary phase. Namely, it has been shown that acrAB-deficient strain can grow to higher cell density in stationary phase than the wild-type E. coli [39] indicating that its cell division is less inhibited Selleck FK506 by stationary phase factors.

In case of P. putida, however, we found no evidence that inactivation of TtgABC pump could affect the growth of bacterial culture in stationary phase, as judged by optical density measurements (data not shown). Nevertheless, flow cytometry analysis of the phenol-exposed P. putida ttgC mutant revealed population structure indicative of more active cell division than that

of the wild-type. However, at this stage of studies we cannot distinguish whether less arrested cell division is a reason for the increased phenol tolerance of the ttgC mutant or, vice versa, increased phenol tolerance results in less-inhibited cell division. In our previous study, find more where we showed that the colR-deficient P. putida is less tolerant to phenol than its parental strain, we argued that membrane permeability of the colR mutant to phenol may be increased [8]. However, results of the current study suggest that the phenol entry into the colR-deficient strain is not increased. The latter was supported by the assay which measured the ability of glucose-grown cells to survive in the presence of 50 mM phenol. Unexpectedly, no differences in cell survival between Non-specific serine/threonine protein kinase the wild-type and the colR-deficient strain

were recorded after phenol-shock, indicating similar membrane permeability to phenol in the colR-deficient and the wild-type cells. As phenol is known to cause membrane permeabilization [40] we therefore tested whether population of phenol-exposed colR-deficient strain could contain more cells with PI permeable membrane. However, as judged by flow cytometry analysis of gluconate-grown bacteria, also the membrane permeabilizing effect of phenol is similar to the wild-type and the colR mutant (Fig. 5). Thus, other reasons than enhanced phenol entry or increased membrane permeability should underlie behind the lowered phenol tolerance of the colR mutant. Interestingly, population analysis at single cell level revealed that compared to the wild-type, phenol more efficiently enhanced the relative amount of subpopulations with higher DNA content in case of the colR mutant, suggesting that cell division of the colR mutant is more sensitive to phenol inhibition than that of the wild-type (Fig. 5). However, it is hard to distinguish whether it occurs due to lowered phenol tolerance or reflects some sort of specific response.