Temperature-specific expression of cspA1 contributes to activation of sigX during pathogenesis and intracellular survival in Pseudomonas plecoglossicida

Abstract

sigX, encoding the extracytoplasmic function sigma factor SigX, was found to be highly expressed in Pseudomonas plecoglossicida at its virulent temperature. Previous RNA-seq analysis also revealed that sigX might be a key virulence gene, which could affect the Epinephelus coioides immune response against P. plecoglossicida. Despite the necessity of sigX for virulence in P. plecoglossicida, how sigX senses and response to temperature changes, and how sigX regulates P. plecoglossicida virulence remain unclear. To illuminate these, we initially analyzed the promoter regions of the sigX and found the presence of a putative CspA box. EMSA and LacZ reporter gene analysis revealed that CspA1 is required for the expression of sigX. Consistent with a role in temperature sensing, CspA1-mediated regulation of sigX is influenced by the culture temperature. Further investigations revealed that sigX is necessary for motility and biofilm formation under virulent temperature, while cspA1 expression has been reported to be induced at virulent temperature and participate in P. plecoglossicida motility and biofilm formation regulation. Meanwhile, the intracellular survival rates and immune escape rates decreased significantly after the knockout of cspA1 and sigX. Moreover, the overlap between SigX and CspA1 regulons is very limited and only one gene is predicted to be regulated by both factors, which is identified as gabD and verified via the EMSA analysis. Together, these data suggest that CspA1 contributes to virulence in a temperature-specific manner via regulating sigX expression.