Investigating the role of the carbon storage regulator A (CsrA) in Leptospira spp.
Résumé
Carbon Storage Regulator A (CsrA) is a well-characterized post-transcriptional global regulator that plays a critical role in response to environmental changes in many bacteria. CsrA has been reported to regulate several metabolic pathways, motility, biofilm formation, and virulence-associated genes. The role of csrA in Leptospira spp., which are able to survive in different environmental niches and infect a wide variety of reservoir hosts, has not been characterized. To investigate the role of csrA as a gene regulator in Leptospira , we generated a L . biflexa csrA deletion mutant (Δ csrA ) and csrA overexpressing Leptospira strains. The Δ csrA L . biflexa displayed poor growth under starvation conditions. RNA sequencing revealed that in rich medium only a few genes, including the gene encoding the flagellar filament protein FlaB3, were differentially expressed in the Δ csrA mutant. In contrast, 575 transcripts were differentially expressed when csrA was overexpressed in L . biflexa . Electrophoretic mobility shift assay (EMSA) confirmed the RNA-seq data in the Δ csrA mutant, showing direct binding of recombinant CsrA to flaB3 mRNA. In the pathogen L . interrogans , we were not able to generate a csrA mutant. We therefore decided to overexpress csrA in L . interrogans . In contrast to the overexpressing strain of L . biflexa , the overexpressing L . interrogans strain had poor motility on soft agar. The overexpressing strain of L . interrogans also showed significant upregulation of the flagellin flaB1 , flaB2 , and flaB4 . The interaction of L . interrogans rCsrA and flaB4 was confirmed by EMSA. Our results demonstrated that CsrA may function as a global regulator in Leptospira spp. under certain conditions that cause csrA overexpression. Interestingly, the mechanisms of action and gene targets of CsrA may be different between non-pathogenic and pathogenic Leptospira strains.
