Comparative genomic and transcriptomic analyses reveal distinct response strategies to hypoxia by Vibrio parahaemolyticus isolates of clinical and aquatic animal origins

Abstract

Vibrio parahaemolyticus is a leading seafood borne pathogen worldwide. The aim of this study was to decipher the response mechanism of V. parahaemolyticus isolates of clinical and aquatic animal origins to the hypoxic condition, which challenges the bacterial survival in the host and in the environment. Growth profiles of V. parahaemolyticus isolates (n = 5) of clinical and aquatic animal origins were examined at different stress conditions (osmolality, acid, temperature, and O2 concentrations). Draft genomes of the V. parahaemolyticus isolates were determined using the Illumina sequencing technique. Comparative genomic analysis were performed to identify and validate the hypoxic tolerance-related genes. The V. parahaemolyticus isolates had an oxygen concentration-dependent growth mode, and the 10% O2 condition strongly inhibited the bacterial growth, when incubated in TSB medium (pH 8.5, 3% NaCl) at 37 °C. Unexpectedly, in marked contrast to the normal 21% O2 condition, the 10% O2 treatment for 24 h significantly increased biofilm formation of V. parahaemolyticus isolates (p < 0.05). Draft genome sequences of four V. parahaemolyticus isolates of aquatic animal origins were determined (4.914–5.3530 Mb), which carried mobile genetic elements (n = 12–29). Genome-wide gene expression changes triggered by the hypoxic condition were further examined. Comparative transcriptomic analyses unveiled multiple molecular strategies employed by the bacterium to mitigate the cell damage caused by the hypoxia. Of note, the pathogenic V. parahaemolyticus ATCC17802 down-regulated and/or shut down ten metabolic pathways to reduce cell viability and maintain cell structure under the hypoxic stress. The results of this study fill prior gaps in the response mechanism of V. parahaemolyticus to the hypoxic condition. Different tolerance to hypoxia contributes to the persistence of pathogenic V. parahaemolyticus in the niches.