Fitness and transcriptomic analysis of pathogenic Vibrio parahaemolyticus in seawater at different shellfish harvesting temperatures

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 degrees C and 30 degrees 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 degrees 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 degrees 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 degrees C. This might be one reason for the lower growth rates of the trh+ strain at 30 degrees C. Histidine metabolism and biofilm formation pathways were significantly downregulated in both strains at 10 degrees C. No significant difference was observed for virulence-associated gene expression between 10 degrees C and 30 degrees C, regardless of the strains.

Automated summary

In this study, the population dynamics of Vibrio parahaemolyticus (Vp) strains with different virulence genes were characterized by inoculating them into seawater at temperatures mimicking different seasons. The transcriptomic responses of the strains containing the thermostable direct hemolysin (tdh+) gene and the tdh-related hemolysin (trh+) gene were investigated. The results showed that the tdh+ strain had a higher growth rate than the trh+ strain at 30 degrees C, while there was no difference between the two strains at 10 degrees C. The RNA sequencing results revealed specific metabolic changes in the trh+ strain at 30 degrees C and downregulation of histidine metabolism and biofilm formation pathways in both strains at 10 degrees C. The expression of virulence-associated genes did not differ significantly between the two temperatures.