Genomic sequencing reveals htpX is a novel spoilage factor from foodborne pathogen Aeromonas veronii: Insights into extracellular enzymes, biofilm formation, stress tolerance, virulence and spoilage.

Abstract

The spoilage bacterium Aeromonas veronii poses increasing risks to the safety of edible bivalves, yet the regulatory mechanisms of its key spoilage factors remain largely unknown. In this study, a foodborne pathogen A. veronii GL2 was isolated from edible Hyriopsis cumingii and its genomic sequencing was conducted, in which the mRNA level of metalloprotease-encoded gene htpX was significantly upregulated under thermal processing. A htpX-defected mutant (ΔhtpX) was then constructed to investigate its role in virulence and spoilage potentials. Although htpX deficiency did not affect growth or proteolytic activity, it remarkably impaired biofilm formation, hemolytic activity and stress tolerance. In the hemolymph model of H. cumingii, ΔhtpX exhibited lower survival rates in supernatant and decreased cytotoxicity toward hemocytes. Further detection of virulence demonstrated that ΔhtpX exhibited an 18.5-fold higher LD50 value than GL2, and reduced bacterial loads in edible portions (foot, adductor muscle). Besides, the spoilage potentials of ΔhtpX were markedly attenuated, in which decreased bacterial proliferation further suppressed the levels of TCA-soluble peptide, TVB-N and pH. In conclusion, these results reveal htpX as a novel determinant linking protein quality control to spoilage and virulence in A. veronii, and provide a novel target for developing control strategies against A. veronii contamination in aquatic products.