Regulation of Neurotoxin Production and Sporulation by a Putative agrBD Signaling System in Proteolytic Clostridium botulinum

Abstract

A significant number of genome sequences of Clostridium botulinum and related species have now been determined. In silico analysis of these data revealed the presence of two distinct agr loci (agr-1 and agr-2) in all group I strains, each encoding putative proteins with similarity to AgrB and AgrD of the well-studied Staphylococcus aureus agr quorum sensing system. In S. aureus, a small diffusible autoinducing peptide is generated from AgrD in a membrane-located processing event that requires AgrB. Here the characterization of both agr loci in the group I strain C. botulinum ATCC 3502 and of their homologues in a close relative, Clostridium sporogenes NCIMB 10696, is reported. In C. sporogenes NCIMB 10696, agr-1 and agr-2 appear to form transcriptional units that consist of agrB, agrD, and flanking genes of unknown function. Several of these flanking genes are conserved in Clostridium perfringens. In agreement with their proposed role in quorum sensing, both loci were maximally expressed during late-exponential-phase growth. Modulation of agrB expression in C. sporogenes was achieved using antisense RNA, whereas in C. botulinum, insertional agrD mutants were generated using ClosTron technology. In comparison to the wild-type strains, these strains exhibited drastically reduced sporulation and, for C. botulinum, also reduced production of neurotoxin, suggesting that both phenotypes are controlled by quorum sensing. Interestingly, while agr-1 appeared to control sporulation, agr-2 appeared to regulate neurotoxin formation.

The Key Sigma Factor of Transition Phase, SigH, Controls Sporulation, Metabolism, and Virulence Factor Expression in Clostridium difficile

“…This also indicates the existence of complex regulatory networks modulating gene expression between these two growth phases, in agreement with the 29 genes encoding transcriptional regulators that are differentially expressed in these two conditions. Interestingly, the agrD gene, encoding an autoinducer prepeptide, was 2.5-fold induced at 10 h, suggesting that a system of quorum sensing could play a role at the end of exponential growth, as observed in several Gram-positive bacteria, including Clostridium perfringens and Clostridium botulinum (11,36). Finally, the expression of genes encoding six sigma factors (sigA2, sigB, sigH, sigF, sigE, and sigG), including 4 out of 5 sigma factors involved in the sporulation process and one sigma factor sharing similarities with SigB, which is involved in the general stress response in Gram-positive bacteria, was induced at 10 h in our transcriptome analysis, in agreement with the major changes detected in the transcriptional patterns.…”

Role of the Agr-Like Quorum-Sensing System in Regulating Toxin Production by Clostridium perfringens Type B Strains CN1793 and CN1795

“…Agr-like QS systems were also recently identified in several pathogenic clostridial species, where they are similarly becoming implicated in virulence (3,5,13,21,22). For example, it was demonstrated that the Agr-like QS system is necessary for C. perfringens type C strain CN3685 to cause either necrotic enteritis or enterotoxemia in animal models (22).…”

Potential Emergence of Multi-quorum Sensing Inhibitor Resistant (MQSIR) Bacteria

“…Clostridium are noted to contain either single or multiple QSS, such as: (1) LuxS, (2) Agr, (3) Agr2 that are regulated by peptide signals e.g., AIP ( Table 1) [24][25][26][27][28][29]. Table 1) [30][31][32][33][34].…”