RNA-seq analysis unveils temperature and nutrient adaptation mechanisms relevant for pathogenicity in Vibrio parahaemolyticus

Abstract

Shrimp diseases frequently occur during pre-adult to adult lifestages, when the rearing water temperature and nutrient levels are high. This phenomenon provides clues that the virulence of pathogens might be induced by elevated temperature and nutrient, whereas the underlying molecular mechanism is lacking. To address this pressing knowledge, we explored how elevated temperature and nutrient stimulate the expression profiles of Vibrio parahaemolyticus, a notorious pathogen causing shrimp acute hepatopancreatic necrosis disease (AHPND). The stimulated pathogenicity was verified by pretreatment of V. parahaemolyticus under elevated temperature or nutrient condition, which caused significantly faster and higher rate of shrimp mortality. RNA-Seq analysis revealed that elevated temperature and nutrient significantly altered the transcriptional patterns of V. parahaemolyticus, resulting in 232 and 82 differential genes, respectively. Weighted Gene Co-Expression Network Analysis depicted that the two conditions induced different gene expression patterns. Specifically, elevated temperature enriched genes involved in arginine biosynthesis and flagellar assembly, whereas elevated nutrition stimulated genes facilitating citrate cycle, cysteine and methionine metabolism pathways. Based on the profiles of differential genes, we inferred that high temperature negatively regulated OpaR and ToxR, thereby activating type VI secretion system 1 (T6SS1). Concurrently, the induced expressions of adhesion Multivalent Adhesion Molecule 7 (MAM7) and flagella-related genes enable V. parahaemolyticus to actively attack host under elevated temperature. By contrast, elevated nutrient activates the T6SS1 through TfoY. These findings provide comprehensive insights into the molecular mechanism implicating in the pathogenicity of V. parahaemolyticus, and partially explain why disease frequency is increased under the scenarios of increasing temperature and eutrophication in aquaculture and natural ecosystems.