Moreover, the mechanism of rgg 0182 expression seemed to be more complex

than that of rgg 1358 since not only influenced by the culture medium but also by the temperature. Further experiments will be done (i) to determine whether the QS mechanism involving the SHP1358 and the Rgg1358 can be generalized to other SHP/Rgg pairs, including SHP0182/Rgg0182 pair and (ii) to understand the mechanism by which temperature could influence the rgg 0182 expression. On the other hands, induction of the rgg 0182 expression at 30°C suggests that this gene might participate in the physiological adaptation of S. thermophilus to this temperature. When cells were cultivated in CDM at 30°C, the inactivation of rgg 0182 was associated with a reduce PXD101 in vivo expression of genes encoding chaperone and protease proteins. In Bacillus subtilis, the DnaKJ complex facilitates substrates buy Sotrastaurin folding to the native state and the GroESL complex provides an isolated environment for the proper folding of small protein substrates [32]. The degradation of unfolded proteins and small peptides is ensured by a protease complex composed of the protease subunit ClpP and several ATPases of the Clp family

[32]. Thus, the Rgg0182 is a transcriptional regulator whose biological roles would be to control the homeostasis of chaperone and protease proteins in cells grown at 30°C in CDM. This is in concordance with data obtained in S. pyogenes where Rgg is found (at the protein PF-01367338 nmr level) to control the expression of ClpL, ClpP, GroEL and DnaK in stationary phase (4). Furthermore, it was shown that ClpL protein of S. thermophilus Sfi39 is necessary for correct response to both heat and cold stresses [4]. Results of qPCR experiments also showed an effect of Rgg0182 on hrcA expression. However, preliminary EMSA results (data not shown) indicated that

the Rgg0182 protein did not bind to the hrcA promoter region. This suggests that the transcription of hrcA obviously is stimulated by Rgg0182 indirectly, perhaps by influencing the expression of another regulatory protein. Such indirect regulation has already been reported for other Rgg proteins CYTH4 [12, 13, 21] and, in the present study, might be extended to, at least, some of the rgg 0182 distal target genes. Finally, to assess the significance of Rgg-associated changes in the expression of genes involved in the heat shock response, we checked whether the deletion of rgg 0182 had an impact on the survival of the strains under heat stress conditions (shift from 30°C to 52°C for 15 min to 60 min). Interestingly, an impaired survival of the mutant was observed but only when the cells were cultivated in the CDM medium, i.e. in conditions where the difference in the level of rgg 0182 transcripts was maximal between both strains. In the mutant cultivated in CDM, the percent of survival decreased with the duration of the heat exposure.