The LexA repressor was also found to interact within PaLoc with operator identified 525 base pairs upstream of PF 01367338 the toxin A gene (tcdA). While the regulation of toxin production in C. difficile is controlled in response to several environmental signals mediated by pleiotropic regulators (CcpA, CodY, SigD and SigH [26]), the possible regulation through the SOS system sheds new light on

this issue. Furthermore, the subinhibitory concentration of SOS-inducing antibiotic ciprofloxacin was recently shown to increase the Toxin A gene expression in C. difficile[27]. Our SPR analysis revealed that also housekeeping genes required for ribosome function (rplR) and β subunit RNA polymerase (rpoB) belong to the LexA regulon, a feature of the SOS network not yet observed in bacteria. Thus, blockage of LexA self-cleavage could impede pivotal functions in C. NCT-501 mouse difficile and this might provide a new approach to treat C. difficile infections. FRAX597 supplier Moreover, although putative SOS genes are present in most of the analysed genomes, several of these genes encoding for putative cell wall hydrolase, transposase and for two component sensor histidine kinase seem to be regulated by LexA only in the 027 ribotype strains (Table 1). The in silico analysis showed operators in front of several genes upregulated exclusively

in ribotype 075 and 027 (celG, vanR, ABC-type transport system). Furthermore, among the analysed genomes, exclusively in the closely related ribotypes 078, 126 and 033, the LexA target site was not found in front of the soj (regulation of DNA replication) tuclazepam and the phnH (phosphonate metabolism protein). Thus the mode of SOS regulation might be related to phylogenetic lineages. Figure 3 C. difficile LexA regulon genes. (A) SPR sensorgrams of the binding of C. difficile LexA with in silico predicted target DNA sites. Selection of LexA target genes

determined by in silico and analysed by SPR. LexA (20 nM) was injected for 60 s across the chip-immobilized DNA fragments containing either of the putative operators and dissociation was followed for 540 s. The representative sensorgrams are shown and the dissociation constants presented as average values of triplicate experiments presented with standard deviation. By n.d. we mark if dissociation rate constant was not determined and the response units are marked by RU. With the MEME tool determined motifs for the target DNA sites found in promoter regions of the genes higher affinity CDR20291_2056, lexA, uvrB, recA, sspB, ruvC, CDR20291_2689, oppC, tcdA, 97b34v1_250108, showing high affinity for LexA (B) or of the genes rplR, rpoB, soj, potC, vanR, CDR20291_2297 to which LexA does not bind stably (C). Cross-reaction of SOS system components in E. coli and C. difficile Induction of SOS gene expression is synchronized and the level, timing and duration of expression of the individual LexA regulon genes differs significantly (1). In E.