Abstract
Vibrio parahaemolyticus is a leading seafood-borne pathogen that can cause acute gastroenteritis and even death in humans. In aquatic ecosystems, phages constantly transform bacterial communities by horizontal gene transfer. Nevertheless, biological functions of prophage-related genes in V. parahaemolyticus remain to be fully unveiled. Herein, for the first time, we studied one such gene VpaChn25_0724 encoding an unknown hypothetical protein in V. parahaemolyticus CHN25. This gene deletion mutant ΔVpaChn25_0724 was constructed by homologous recombination, and its complementary mutant ΔVpaChn25_0724-com was also obtained. The ΔVpaChn25_0724 mutant exhibited a sever defect in growth and swimming motility particularly at lower temperatures. Biofilm formation and cytotoxicity capacity of V. parahaemolyticus CHN25 was significantly lowered in the absence of VpaChn25_0724. Comparative secretomic analysis revealed an increase in extracellular proteins of ΔVpaChn25_0724, which likely resulted from its damaged cell membrane. Comparison of transcriptome data showed twelve significantly altered metabolic pathways in ΔVpaChn25_0724, suggesting inactive transport and utilization of carbon sources, repressed energy production and membrane biogenesis in ΔVpaChn25_0724. Comparative transcriptomic analysis also revealed several remarkably down-regulated key regulators in bacterial gene regulatory networks linked to the observed phenotypic variations. Overall, the results here facilitate better understanding of biological significance of prophage-related genes remaining in V. parahaemolyticus.
Highlights
Vibrio parahaemolyticus is a gram-negative bacterium and thrives in marine, riverine, and aquaculture environments worldwide (Ghenem et al, 2017)
The E. coli strains were routinely incubated in Luria-Bertani (LB) medium (1% NaCl, pH 7.2) at 37°C, and the V. parahaemolyticus strains were grown in LB (3% NaCl, pH 8.5) or Tryptic Soy Broth (TSB) (3% NaCl, pH8.5) media
Comparative genomic analysis revealed that the largest prophage gene cluster in V. parahaemolyticus CHN25 genome has sequence similarity to the Vibrio phage Martha 12B12 that contains 50 predicted genes
Summary
Vibrio parahaemolyticus is a gram-negative bacterium and thrives in marine, riverine, and aquaculture environments worldwide (Ghenem et al, 2017). Consumption of raw, undercooked or mishandled seafood contaminated by pathogenic V. parahaemolyticus can cause acute gastroenteritis in humans and even death (Kim et al, 2017). Most pathogenic V. parahaemolyticus strains of clinical origin have two major virulence factors, a thermostable direct hemolysin (TDH) and a TDH-related hemolysin (TRH). Both toxins have hemolytic activity, enterotoxin activity, cardiotoxicity and cytotoxicity to the host (Li et al, 2019). Some V. parahaemolyticus isolates of environmental origins lacking the tdh and/or trh genes show cytotoxicity to human intestinal cells, suggesting additional virulence-associated factors exist in the bacterium (Raghunath, 2014). Identification of risk factors in V. parahaemolyticus is imperative for assuming food safety
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