| Summary: | ABSTRACT To better characterize the population dynamics of Vibrio parahaemolyticus (Vp) containing different virulence genes, two Vp strains were inoculated into seawater separately and incubated at temperatures (10°C and 30°C) mimicking winter and summer pre-harvest shellfish rearing seasons. The cellular responses of two Vp strains, one containing the thermostable direct hemolysin (tdh+) gene and the other one containing tdh-related hemolysin (trh+) gene, were studied at the transcriptomic level. Results showed that, at 30°C, tdh+ and trh+ strains reached 6.77 ± 0.20 and 6.14 ± 0.07 log CFU/mL, respectively, after 5 days. During this time, a higher growth rate was observed in the tdh+ strain than in the trh+ strain. When being kept at 10°C, both Vp strains persisted at ca. 3.0 log CFU/mL in seawater with no difference observed between them. Survival and growth models were then established based on the Baranyi equation. The goodness-of-fit scores ranged from 0.674 to 0.950. RNA sequencing results showed that downregulated central energy metabolism and weakened degradation of branched-chain amino acid were observed only in the trh+ strain not in the tdh+ strain at 30°C. This might be one reason for the lower growth rates of the trh+ strain at 30°C. Histidine metabolism and biofilm formation pathways were significantly downregulated in both strains at 10°C. No significant difference was observed for virulence-associated gene expression between 10°C and 30°C, regardless of the strains. IMPORTANCE Given the involvement of Vibrio parahaemolyticus (Vp) in a wide range of seafood outbreaks, a systematical characterization of Vp fitness and transcriptomic changes at temperatures of critical importance for seafood production and storage is needed. In this study, one of each virulent Vp strain (tdh+ and trh+) was tested. While no difference in survival behavior of the two virulent strains was observed at 10°C, the tdh+ strain had a faster growth rate than the trh+ strain at 30°C. Transcriptomic analysis showed that a significantly higher number of genes were upregulated at 30°C than at 10°C. The majority of differentially expressed genes of Vp at 30°C were annotated to functional categories supporting cellular growth. At 10°C, the downregulation of the biofilm formation and histidine metabolism indicates that the current practice of storing seafood at low temperatures not only protects seafood quality but also ensures seafood safety.
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