Genome and Transcriptome Analyses of Vibrio vulnificus FORC_037 Isolated from Raw Seafood

Abstract

Vibrio vulnificus naturally inhabits the coastal marine environments worldwide and is an opportunistic pathogen for humans as it may cause severe wound infections, gastroenteritis or life-threatening sepsis in susceptible individuals. To study this important pathogen at the genomic level, V. vulnifcus FORC_037 was isolated from soft-shell clam (Mya arenaria oonogai) and its whole genome was sequenced using Illumina MiSeq and PacBio platforms. The strains genome, which is composed of two chromosomes and a plasmid, altogether contains 4,506 open reading frames, 118 tRNA, and 34 rRNA genes. Genes encoding several hemolysins, and iron uptake-related proteins were found by BLAST. Average nucleotide identity (ANI) analysis of FORC_037s genome with nine other completely sequenced V. vulnificus genomes showed that the genome, while being an outlier, is most closely related to those of FORC_017 and CMCP6. Comparative genome analysis of FORC_037 and CMCP6, a clinical isolate, revealed that FORC_037 has additional virulence factors such as accessory cholera enterotoxin (FORC37_3618) and zonula occludens toxin (FORC37_3619). This may explain why, despite being an environmental isolate, FORC_037 exhibits a high level of cytotoxicity toward INT-407 human epithelial cells as evidenced by lactose dehydrogenase (LDH) release assay. To further probe the genetic program of the strain upon contact with small octopus (Octopus minor), which is often consumed raw in Korea, transcriptome sequencing was used. Transcriptome analysis hinted that V. vulnificus uses the seafood as a reservoir as genes related to adhesion, galactose utilization, oxidative stress resistance and iron-uptake were upregulated and genes related to motility were downregulated. Interestingly, a number of putative virulence factors were upregulated, including genes involved in vulnibactin utilization, and type II secretion system which is associated with pilus assembly. This may explain illness following consumption of the seafood. This report will help prevent V. vulnificus outbreaks in the future by providing genomic and transcriptomic insights on the species.