coli and B. subtilis. Overall, the qPCR analysis validates

our statistical analysis of the microarray data based on the common variance model associated with the correction of Bonferroni (Table 2). Indeed, although calculated expression ratios were very similar for comFA and ssb (around 1.5), the former, which had an associated P value < 0.05 with the Bonferroni correction, was confirmed as overexpressed in the qPCR analysis, whereas the latter (which passed the other applied statistical test) was found to be almost unaffected by σH in the qPCR analysis (Table 2). Therefore, we expect that all genes with a better score than comFA in the microarray anlaysis (i.e. P value Bonferroni ≤ 1.54 E-02) are good

candidates for belonging to the σLsa H regulon. Altogether, results of this study thus identify 25 genes as belonging to the σLsa H regulon. BKM120 chemical structure Some genes (e.g., ATM/ATR inhibitor dprA), while truly activated by σLsa H, may not be detected in this microarray experiment, indicating the need for further studies to define the full regulon. Transcriptional reprogramming caused by sigH Lsa overexpression is consistent with the existence of a competent state in L. sakei, supported by the observed up-regulation of com genes involved in pseudopilus morphogenesis and DNA translocation as well as of dprA (which shares 47% aa identity with the S. pneumoniae dprA gene product). ssb and recA appear little or not activated one hour after sigH Lsa induced overexpression, whereas their level of induction during the competence state in S. pneumoniae and B. learn more subtilis reportedly varies from 5 to over ten-fold [32, 35]. These genes might be transiently regulated (in a narrower window than com operons and dprA), regulated by other factors, or their up-regulation may not be required in L. sakei. Indeed both genes participate in the bacterial vegetative life cycle and are expected to be transcribed at a significant

basal level when cells are not in the competence Thymidine kinase state [36]. Interestingly, L. sakei possesses a unique ssb gene (ssbA-type), whereas B. subtilis and S. pneumoniae have paralog genes [36, 37]. The need for a transformation-dedicated SSB protein has been discussed [37]. Although known natural transformation is frequently associated with multiple ssb in Firmicutes [37], an additional competence-induced SSB may be a facilitator rather than an essential contributor to the transformation process, since transformation frequency is only reduced by two- to ten-fold when ssbB is inactivated in S. pneumoniae or in B. subtilis [36]. Is L. sakei capable of natural genetic transformation? As the σH-activated transcriptome of L. sakei was indicative of a competence state, we looked for genetic transformation in this species. The first strategy involved the overproducer strain sigH(hy)*.