Genome and Transcriptome analyses of Vibrio parahaemolyticus FORC_022

Abstract

Vibrio parahaemolyticus is a Gram negative, curved rod-shaped bacterium that causes gastrointestinal illness associated with the consumption of seafood. To characterize V. parahaemolyticus that have caused outbreaks in South Korea, ten strains of V. parahaemolyticus were obtained from Korean Ministry of Food and Drug Safety. Virulence gene-specific PCR screening and lactate dehydrogenase (LDH) release assay were employed to evaluate the virulence of these strains. Among strains, the V. parahaemolyticus H8 strain, which was isolated from soy sauce marinated crab, showed a higher level of cytotoxicity than the positive control used in the LDH release assay. Therefore, the H8 strain was selected for genome sequencing and was designated as FORC_022. The FORC_022 genome consists of two circular chromosomes and a plasmid.The genome was predicted to have 4,858 open reading frames, 133 tRNA genes, and 37 rRNA genes. The FORC_022 strain did not include major virulence factor such as thermostable direct hemolysin (tdh), and TDH-related hemolysin (trh), but it had many genes related to virulence and several V. parahaemolyticus islands.Phylogenetic tree analysis of Vibrio 16S rRNA sequence showed that all the V. parahaemolyticus strains formed a group, which included the FORC_022 strain as well. Also, average nucleotide identity (ANI) analysis using nine complete V. parahaemolyticus genome sequences available from NCBI revealed that FORC_022 was closely related to the CDC_K4557 strain (98.55%). Comparativegenomic analysis of FORC 022 with CDC_K4557 revealed that FORC 022 carried an additional genomic region encoding virulence factors like Zona occludens toxin and type III secretion factors.To identify differentially expressed genes of V. parahaemolyticus FORC_022exposed to crab, RNA-sequencing was performed. Transcriptome analysis showed thatthe gene related toamino acid transport and metabolism, lipid transport and metabolism were down-regulated and the gene related to carbohydrate transport and metabolism, translation, ribosomal structure were up-regulated. Also, some virulence factors like type III secretion system, Tad locus, thermolabile hemolysin were up-regulated.The results suggested the FORC_022 strain may be pathogenic and there is high risk of infectionwhen human eat crab contaminated strain FORC_022.