thermophilus cold stress response, were also included in this study. The transcript levels of these genes were measured by qPCR on stationary phase GDC-0994 research buy cells of the wild-type and the Δrgg 0182 mutant grown in CDM medium at 30°C (i.e. when rgg 0182 was the most transcribed) from 3 independent experiments done in duplicate (Figure 5). In these conditions, the transcript level of almost all genes encoding protease and chaperone Adriamycin purchase proteins (except that of dnaJ, groEL, cspA and cspB) was under-expressed in the Δrgg 0182 mutant compared to the wild type strain suggesting a role for Rgg0182 in the control of their transcription. The difference

in the transcript abundance between the wild type and Δrgg 0182 mutant strains ranged from learn more 1.5- to 20-fold and were statistically significant (P < 0.001). As described in other Streptococcus transcriptional analysis, a 1.5-fold difference in transcript

level was interpreted as a significant difference in expression between the strains [21, 23]. Figure 5 Relative genes transcript level of S. thermophilus stationary phase cells grown in CDM medium at 30°C. Total RNAs were extracted from stationary phase cells of S. thermophilus LMG18311 (dark gray bars) and its isogenic Δrgg 0182 mutant (light gray bars) grown in CDM at 30°C. Data are presented as the mean +/- standard deviation of the gene transcript levels measured from 3 independent experiments done in duplicate. Student’s t test: *, p < 0.001. In low-GC Gram positive bacteria, the control of the transcription of the clp family acetylcholine genes and of dnaK and groES genes is primarily mediated by binding of the CtsR and HrcA repressors, respectively, to promoter region of target genes. In S. thermophilus LMG18311, we found CtsR operators (AGGTCAAANANAGGTCAAA) [6] upstream of clpP, clpE, clpL, ctsR, clpC and groEL genes and HrcA binding sites (GCACTC(N)9GAGTGCTAA) [30] only upstream of hrcA, groEL (with 2 mismatches) and dnaJ (6 mismatches). These results prompted us to evaluate the level of ctsR and hrcA transcripts (locus tags, stu0076 and stu0118 respectively) in the wild-type and the Δrgg 0182 mutant. These data revealed no significant

difference for ctsR gene whereas the hrcA transcript level was nearly 4-fold reduced in the absence of rgg 0182 suggesting that Rgg0182 positively controls hrcA transcription. These results indicate that Rgg0182 is a positive transcriptional regulator of heat shock proteins encoding genes in particular of hrcA, clpC, clpE, clpL, clpP, clpX, dnaK, groES and hsp33 genes. Role of the rgg 0182 gene in the heat shock response of S. thermophilus Knowing that several rgg genes from pathogenic streptococci are involved in stress response and taking into account the above data, we checked whether rgg 0182 could be involved in the S. thermophilus adaptation to heat shock. The heat tolerance was evaluated on stationary phase cells grown for 10 h in CDM medium (OD600nm = 1.