To this end, the activity of the cit promoters was measured in

To this end, the activity of the cit promoters was measured in

a CcpA-deficient E. faecalis strain (CL14) [27] containing either the pTCV-PcitHO or the pTCV-PcitCL plasmid (strains CL1 and CL2, respectively) (Figure 1C). β-Galactosidase activity was determined in cell extracts of E. faecalis grown in LBC supplemented with the same PTS and non-PTS sugars, described in Figure 1B. As shown in Figure 1C, no small molecule library screening significant repression was observed in the presence of non-PTS sugars and PTS sugars exerted a much weaker repressive effect than in the wild-type strain. However, in these CcpA-defective E. faecalis strains the repression was not completely alleviated. A similar observation was reported for other genes controlled by the CCR in E. faecalis [27]. Subsequently, we tested whether

expression of the cit operons depends on the glucose concentration. Hence, we measured the β-galactosidase activity in wild-type and ccpA mutant strains carrying either one of the two transcriptional cit promoter-lacZ fusions. In the wild-type-derived strains (JHB2 and JHB6) β-galactosidase activity decreased when the initial concentration of glucose was raised from 0.25 to 1% (Figure 2A). On the other hand, in the CcpA-deficient strains (CL1 and CL2) activity of the cit promoters was independent of the glucose concentration (Figure 2B). These results suggest that the activity of the cit promoters is tightly regulated by the availability of glucose and that the pleiotropic transcriptional factor CcpA is involved in this process. Figure find more 2 Effect of glucose concentrations on the expression of cit operons, CitO levels and citrate lyase activity. A and B) JHB2 (JH2-2/pTCV-PcitHO), JHB6 (JH2-2/pTCV-PcitCL), CL1 (CL14/pTCV-PcitHO) and CL2 strains (CL14/pTCV-PcitCL) were grown in LBC (circle) or LBC supplemented with different initial concentrations of glucose: 0.25% (square),

0.5% (up-pointing triangle) and 1% (down-pointing triangle). Gemcitabine supplier The corresponding open symbols indicate the remaining glucose concentration in the culture medium (right axis). Levels of accumulated β-galactosidase activity were measured at different times as indicated in the figure. C and D) E. faecalis strains were grown in the same conditions of panels A and B, and cells extracts were obtained 7 h after inoculation, C) Western blot analysis was performed with polyclonal antibodies raised against CitO. D) Citrate lyase activity was determined as described previously [5]. Error bars represent standard deviation of triplicate measurements. In order to determine whether these differences in transcriptional repression affect the level of the proteins encoded by the cit operons, the amounts of CitO and citrate lyase activity were determined. First, a Western blot using antibodies raised against check details purified CitO was performed with extracts of wild type E. faecalis JH2-2 grown during 7 hs in LBC supplemented with different initial concentrations of glucose (0.25%, 0.5% or 1%).

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