Project description:Genes encoding the alternative sigma factor SigmaB, involved in the general stress response in firmicutes, as well as its regulators are present in the genome of the enteropathogen Clostridium difficile. We inactivated the sigB gene using the ClosTron technology in order to identify the role of this sigma factor in the physiology of this bacterium. Transcriptomic experiments showed that SigB positively and negatively controlls several genes involved in different cellular processes such as metabolism, sporulation and stress response.
Project description:Clostridium difficile is an important nosocomial pathogen and the leading cause of hospital-acquired diarrhea. Antibiotic use is the primary risk factor for the development of C. difficile-associated disease because it disrupts normal protective gut flora and enables C. difficile to colonize the colon. C. difficile damages host tissue by secreting toxins and disseminates by forming spores. The toxin-encoding genes, tcdA and tcdB are part of a pathogenicity locus, which also encodes the gene tcdR that codes for the toxin genes positive regulator. TcdR is an alternate sigma factor that initiates transcription of tcdA and tcdB at their promoters. Alternative sigma factors are known to regulate virulence and virulence associated genes in many pathogenic bacteria. We created a tcdR mutant in the epidemic-type C. difficile R20291 strain in an attempt to identify the global role of tcdR. A site-directed mutation in tcdR affected both toxin production and sporulation in C. difficile R20291. Spores derived from the tcdR mutant were found to be mildly temperature sensitive. Moreover, nearly two fold more taurocholate was needed to germinate spores from the tcdR mutant than the spores prepared from the wild-type parent strain. Comparison of the tcdR mutant transcriptome with the parent strain revealed many differentially expressed late sporulation genes in the tcdR mutant. These data suggests that gene regulatory networks of toxin production and sporulation in Clostridium difficile are linked with each other.
Project description:We illustrate how metabolically distinct species of Clostridia can protect against or worsen Clostridioides difficile infection, modulating the pathogen's colonization, growth, and virulence to impact host survival. Gnotobiotic mice colonized with the amino acid fermenter Paraclostridium bifermentans survived infection while mice colonized with the butyrate-producer, Clostridium sardiniense, more rapidly succumbed. Systematic in vivo analyses revealed how each commensal altered the gut nutrient environment, modulating the pathogen's metabolism, regulatory networks, and toxin production. Oral administration of P. bifermentans rescued conventional mice from lethal C. difficile infection via mechanisms identified in specifically colonized mice. Our findings lay the foundation for mechanistically informed therapies to counter C. difficile disease using systems biologic approaches to define host-commensal-pathogen interactions in vivo.
Project description:Clostridioides difficile is one of the most common nosocomial pathogens and a global public health threat. Upon colonization of the gastrointestinal tract, C. difficile is exposed to a rapidly changing polymicrobial environment and a dynamic metabolic milieu. Despite the link between the gut microbiota and susceptibility to C. difficile, the impact of synergistic interactions between the microbiota and pathogens on the outcome of infection is largely unknown. Here, we show that microbial cooperation between C. difficile and Enterococcus has a profound impact on the growth, metabolism, and pathogenesis of C. difficile.. Through a process of nutrient restriction and metabolite cross-feeding, E. faecalis shapes the metabolic environment in the gut to enhance C. difficile fitness and increase toxin production. These findings demonstrate that members of the microbiota, such as Enterococcus, have a previously unappreciated impact on C. difficile behavior and virulence.
Project description:The intestines house a diverse microbiota that must compete for nutrients to survive, but the specific limiting nutrients that control pathogen colonization are not clearly defined. Clostridioides difficile colonization typically requires prior disruption of the microbiota, suggesting that outcompeting commensals for resources is key in establishing C. difficile infection (CDI). The immune protein calprotectin (CP) is released into the gut lumen during CDI to chelate zinc (Zn) and other essential nutrient metals. Yet, the impact of Zn limitation on C. difficile colonization is unknown. To define C. difficile responses to Zn limitation, we performed RNA sequencing on C. difficile exposed to CP. In media with CP, C. difficile upregulated genes involved in metal homeostasis and amino acid metabolism.
Project description:In Gram-positive organisms the general stress response is regulated by the alternative sigma factor sigma B (σB). In C. difficile this sigma factor has been implicated in protection against stressors such as reactive oxygen species and antimicrobial compounds. Here, we show that an anti-σB antibody can be used to demonstrate overexpression of σB in C. difficile and that this overexpression is tolerated for short periods of time, despite its toxicity. Toxicity associated with σB-overexpression leads to loss of the plasmid used for anhydrotetracycline-induced σB expression. By uncoupling σB from its native regulatory network, we refined the previously proposed σB regulon and confirmed a direct role for σB in the induction of selected genes using in vitro run-off transcription reactions. Finally, using a plate-based luciferase reporter assay we demonstrated that different antibiotics and hydrogen peroxide induce genes positively regulated by σB in a manner dependent on this sigma factor. Together, our work suggests that lethal exposure to antibiotics may result in the formation of toxic radicals that lead to σB-dependent gene activation.
Project description:Gene expression level of Clostridioides difficile (C. difficile) strain R20291 comparing control C. difficile carring pMTL84151 as vector plasmid with C. difficile conjugated with a pMTL84151-03890 gene. Goal was to determine the effects of 03890 gene conjugation on C. difficile strain R20291 gene expression.
Project description:The Gram-positive bacterium Clostridium difficile, a leading cause of antibiotic-associated pseudomembranous colitis, has received increasing attention due to a rising incidence of clinical C. difficile infections (CDI). Despite progress understanding bacterial factors that promote CDI-associated morbidity and mortality, many fundamental aspects of C. difficile biology remain to be explored. Compared to other Gram-positive pathogens, little is known about the bacterium’s transcriptome architecture and in particular mechanisms of post-transcriptional control. To close this knowledge gap, we have applied a suite of transcriptome-focused techniques, including transcription start site mapping (dRNA-seq), transcription termination mapping, and Hfq RIP-seq, resulting in a single-nucleotide resolution RNA map of C. difficile strain 630.