Characterization of Carbon Storage Regulator A (CsrA) homolog as a global gene regulator in Leptospira spp.

Abstract

Leptospira spp. consist of non-pathogenic and pathogenic species. The bacteria can survive in diverse environments and therefore need mechanisms of rapid adaptation to environmental changes. However, molecular mechanisms of stress response in Leptospira are not fully understood. Carbon Storage Regulator A (CsrA) is a well-characterized, conserved, post-transcriptional global regulator that plays a critical role in response to environmental changes in many bacteria. CsrA has been reported to regulate several pathways such as glycogen metabolism, motility, biofilm formation, and virulence-associated genes. Based on available genomics data of Leptospira spp., we found putative csrA homolog, approximately 50% similarity with csrA of E. coli. However, csrA and its function have not been characterized in Leptospira. To investigate the role of csrA as a global gene regulator in Leptospira, csrA mutant, csrA complemented mutant, and csrA overexpressing strains of Leptospira. biflexa serovar Patoc, as well as csrA overexpressing strain of L. interrogans serovar Manilae, were constructed in this study. In comparison to wild type, csrA mutant of L. biflexa serovar Patoc displayed poor growth under starvation condition. However, complementation of csrA could only partially restore the phenotype. The csrA mutant also increased susceptibility to stress caused by H2O2 and ethidium bromide. Although no alteration in motility was observed in both csrA mutant and csrA overexpressing L. biflexa serovar Patoc, flaB2 and flaB3 showed their potential target of CsrA due to significant upregulation in the csrA mutant but significant downregulation in csrA overexpressing strain. In contrast, csrA overexpressing strain of L. interrogans serovar Manilae had poor motility on soft agar and significant upregulation of flaB1, flaB2, and flaB4. We also showed the specific binding of recombinant CsrA of L. interrogans serovar Manilae to the 5’ untranslated region of flaB4 transcript. In conclusion, our data suggested the role of CsrA as a global regulator in Leptospira spp. Interestingly, the mechanisms of action and gene targets of CsrA might be different between non-pathogenic and pathogenic Leptospira strains.