Role of cold shock protein CspA in Aeromonas salmonicida subsp. salmonicida physiology and virulence

Cold shock proteins are small, highly conserved nucleic acid-binding proteins that help bacteria adapt to stress conditions. Aeromonas salmonicida subspecies salmonicida is a psychotropic, Gram-negative intracellular fish pathogen that causes furunculosis in fish. The role of cold shock proteins in the stress response in marine pathogens like A. salmonicida is unknown. In this study, we reported the role of cold shock protein A (CspA) in A. salmonicida physiology, stress response, and virulence in lumpfish (Cyclopterus lumpus). Aeromonas salmonicida ΔcspA was characterized using phenotypic tests and transcriptomics. Aeromonas salmonicida ΔcspA showed a reduction in survival at low temperatures (0 and 4 °C) and in ox bile-containing (5%) conditions. Differential gene expression analysis showed 632 dysregulated genes in ΔcspA. Among these 632 differentially expressed genes (DEGs), 413 were upregulated, and 219 were downregulated. Most downregulated genes were related to the type III secretion system (T3SS). However, A. salmonicida ΔcspA was not fully attenuated in the lumpfish host but delayed fish mortality and reduced tissue colonization after systemic infection in contrast to the wild type strain. Overall, this study provides novel insight into the roles of CspA in virulence and the physiology of A. salmonicida.