Roles of three cold shock proteins in the psychrophilic seafood bacterium Shewanella baltica

Abstract:

[Objective] Shewanella baltica is a specific spoilage microorganism commonly detected in refrigerated seafood at the end of shelf life, while the knowledge about the roles of cold shock proteins (CSPs) in this bacterium is limited. This study aims to unravel the roles of three csp genes in S. baltica SB-19. [Methods] BEAST was employed to study the molecular evolutionary of csp genes in food-derived microorganisms of Gammaproteobacteria, and qPCR to determine the expression patterns of the three csp genes in S. baltica SB-19. The strains with csp gene knockout were constructed, and their growth rates, quorum sensing, spoilage ability were analyzed under different temperatures and environmental stresses. Finally, three strains with heterologous expression of csp were constructed, and their responses to different temperatures and environmental stresses were examined. [Results] Three csp genes, cspC, cspD, and cspG, were identified in S. baltica. All the cspD genes of Gammaproteobacteria formed a monophyletic clade and segregated from other csp genes approximately 1 109.6 million years ago (MYA). The cspC and cspG of S. baltica segregated approximately 858.8 MYA. Both cspC and cspG were involved in the response to cold shock, whereas cspD did not. The knockout and overexpression experiments revealed that cspG was essential for S. baltica survival at low temperature and played a universal role in the response to environmental stress, and cspC aided the bacterial response to stress. The cspD gene was associated with bacterial growth. Furthermore, the result of the experiments with inoculation of knockout strains in fish juice indicated that both cspC and cspG were associated with the spoilage ability of S. baltica below room temperature. [Conclusion] The three csp genes play different roles in S. baltica. The findings pave new ways for the research on the cold adaptation and spoilage mechanism of spoilage microorganisms.