All authors have read and approved the final manuscript.”
“Background Facultative-pathogenic mycobacterial species cause disseminating mycobacterial infections in humans C59 clinical trial that are defective in the acquired immune response (IR). For PD173074 order example, M. kansasii and M. avium are often found as opportunistic pathogens in immunosuppressed individuals due to AIDS. In contrast, non-pathogenic mycobacteria of the M. fortuitum and M. smegmatis group do not cause disseminating disease even in immunosupressed individuals[1]. Therefore, we hypothesized that the inability of non-pathogenic species

to cause disease could be due to their strong capacity to induce an innate IR, which is sufficient to defend against these species of mycobacteria even in individuals with defective acquired immunity. The capacity of infected macrophages to undergo apoptosis after infection is an efficient mechanism of innate IR against mycobacteria[2]. Indeed, the induction of apoptosis of infected macrophages may induce direct

killing of intracellular mycobacteria [3, 4]. In addition, mycobacteria contained in apoptotic bodies can be taken up via phagocytosis by uninfected bystander macrophages which are then able to kill the bacteria more efficiently [5]. Furthermore the importance of macrophage apoptosis for the IR was underscored by the recent findings that host susceptibility or resistance to mycobacterial infections could be linked to the capacity of the infected macrophages to undergo necrosis Dorsomorphin mw or apoptosis, respectively[6]. Consistently, virulent M. tuberculosis strains express proteins implicated in inhibiting host cell apoptosis such

as the superoxide dismutase A (SodA), catalase G (KatG) and NuoG which is part of the NDH-1 protein complex. The deletion of any of these genes strongly attenuates the virulence of the bacteria suggesting that host cell apoptosis inhibition is a virulence pathway [7–9]. In primary human alveolar macrophages the facultative-pathogenic Thymidylate synthase mycobacteria (M. kansasii and M. bovis BCG) induced significantly more apoptosis then four different virulent strains of M. tuberculosis after 5 days of infection [10]. Interestingly, M. smegmatis induces significant apoptosis in differentiated human THP-1 cells after only 24 h [8], suggesting the presence of potent mycobacterial ligands capable of inducing host cell signaling. The phospho-myo-inositol-lipoarabinomannan (PI-LAM) isolated from the cell wall of an unidentified fast-growing mycobacterial species, also referred to Ara-LAM, could be one such ligand, since it has been shown to induce host cell apoptosis [11, 12].

We used the P. aeruginosa PAO1 strain containing pAB134, which

carries the luxCDABE operon under the control of the rhlG promoter region (prrhlG), extending from − 413 to −23 relative to the first base of the rhlG translation initiation codon. We chose this strain since the multi-copy pAB134 plasmid led to higher amounts of mRNAs than the genomic mono-copy rhlG gene, thereby facilitating the experiment. Three internal luxCDABE primers this website were used to synthesize cDNAs and amplify them by PCR. A mix of two DNA fragments, both of ~ 400 pb was obtained after the last PCR. They were sequenced, identifying two different transcription start sites at positions −113 and −55 relative to the rhlG translation initiation codon (Figure 1). The weakest signal (−55) corresponded to the transcription start site previously identified by Campos Garcia et al. [4] as arising from a σ70-dependent promoter. The strongest signal (−113) revealed a novel transcription start site preceded by the selleck chemicals llc sequence CAACCT − N16 − TCTG,

selleck chemical which is similar to the consensus sequence for AlgU-dependent promoters, GAACTT − N16–17 − TCTG [20]. AlgU is the extra-cytoplasmic function (ECF) sigma factor involved in alginate overproduction leading to mucoidy, response to some stresses, and biofilm stability [21–23]. Figure 1 Promoter mapping of rhlG. A: Schematic representation of the rhlG locus. Black flags indicate the promoters PAlgU, Pσ54, and Pσ70; and arrows indicate the rhlG and PA3388 genes. B: Annotated sequence of the rhlG promoter region. Black triangles indicate the three transcription start sites (+1) and the negative numbers provide their position relative to the rhlG translation initiation codon. The promoter sequences recognized by the sigma factors AlgU, σ54, and σ70 are respectively point over lined, full trait over lined, and underlined. The “lux box” as proposed in [4] is boxed with the two highly conserved dinucleotides enough underlined. The

chromatograms show the results of 5′-RACE PCR allowing us to identify the major transcription start sites resulting from PAlgU and the minor from 1 Pσ70, the white arrow corresponding to the last base before the polyC tail added to the 5′ extremity of cDNA. The transcription start site resulting from Pσ54 was identified in [4]. The pAB134 plasmid was primarily constructed to quantify the prrhlG activity in the course of bacterial growth by measuring the luminescence resulting from the LuxCDABE proteins. To verify the role of AlgU in the transcription of rhlG, P. aeruginosa PAO1 and its algU mutant strain PAOU [21] were transformed by pAB133 (containing the promoter-less luxCDABE operon, used to quantify the luminescence baseline) and pAB134. Strains were grown in PPGAS medium and luminescence was followed during 30 h.