Nitric oxide (NO) and its derivatives are important effectors of host innate immunity, disrupting cellular function of infecting pathogens. Transcriptome analysis of Vibrio vulnificus, an opportunistic human pathogen, identified a set of genes induced upon exposure to NO. Among them, VvhmpA (V. vulnificus hmpA), encoding a multidomain NO dioxygenase, was the most greatly induced upon exposure to NO and was thus further characterized. Absorption spectra demonstrated that VvHmpA is a heme protein in which the heme iron can exist in either reduced, NO-bound, or oxidized state. Biochemical studies revealed that VvHmpA is a flavohemoglobin containing equimolar amounts of heme and FAD as cofactors. The KM and kcat values of VvHmpA for NO at 37°C, the temperature encountered by V. vulnificus in the host, were greater than those at 30°C, indicating that VvHmpA detoxifies high levels of NO effectively during infection. Compared with the wild type, the VvhmpA mutant exhibited a lower NO-decomposition activity and impaired growth in the presence of NO in vitro. Also, the cytotoxicity and survival of the VvhmpA mutant infecting the NO-producing murine macrophage cells were lower than those of the wild type. Furthermore, the mouse lethality of the VvhmpA mutant was reduced compared to that of the parental wild type. The combined results revealed that VvHmpA is a potent virulence factor that is induced upon exposure to NO and important for the survival and pathogenesis of V. vulnificus during infection.

BackgroundVibrio vulnificus, a resident in the human gut, is frequently found in seafood, causing food-borne illnesses including gastroenteritis and severe septicemia. While V. vulnificus has been known to be one of the major food-borne pathogens, pathogenicity and virulence factors are not fully understood yet. To extend our understanding of the pathogenesis of V. vulnificus at the genomic level, the genome of V. vulnificus FORC_017 isolated from a female patient experiencing a hemorrhagic rash was completely sequenced and analyzed.ResultsThree discontinuous contigs were generated from a hybrid assembly using Illumina MiSeq and PacBio platforms, revealing that the genome of the FORC_017 consists of two circular chromosomes and a plasmid. Chromosome I consists of 3,253,417-bp (GC content 46.49 %) containing 2943 predicted open reading frames (ORFs) and chromosome II of 1,905,745-bp (GC content 46.90 %) containing 1638 ORFs. The plasmid pFORC17 consists of 70,069-bp (GC content 43.77 %) containing 84 ORFs. The average nucleotide identity (ANI) value of the FORC_017 and CMCP6 strains was 98.53, suggesting that they are closely related.ConclusionsPathogenesis-associated genes including vvhA, rtx gene cluster, and various hemolysin genes were present in FORC_017. In addition, three complete secretion systems (Type I, II and VI) as well as iron uptake-related genes for virulence of the FORC_017 were detected, suggesting that this strain is pathogenic. Further comparative genome analysis revealed that FORC_017 and CMCP6 share major toxin genes including vvhA and rtx for pathogenesis activities. The genome information of the FORC_017 provides novel insights into pathogenicity and virulence factors of V. vulnificus.Electronic supplementary materialThe online version of this article (doi:10.1186/s13099-016-0104-6) contains supplementary material, which is available to authorized users.

This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

BackgroundFoodborne illness can occur due to various pathogenic bacteria such as Staphylococcus aureus, Escherichia coli and Vibrio parahaemolyticus, and can cause severe gastroenteritis symptoms. In this study, we completed the genome sequence of a foodborne pathogen V. parahaemolyticus FORC_014, which was isolated from suspected contaminated toothfish from South Korea. Additionally, we extended our knowledge of genomic characteristics of the FORC_014 strain through comparative analysis using the complete sequences of other V. parahaemolyticus strains whose complete genomes have previously been reported.ResultsThe complete genome sequence of V. parahaemolyticus FORC_014 was generated using the PacBio RS platform with single molecule, real-time (SMRT) sequencing. The FORC_014 strain consists of two circular chromosomes (3,241,330 bp for chromosome 1 and 1,997,247 bp for chromosome 2), one plasmid (51,383 bp), and one putative phage sequence (96,896 bp). The genome contains a total of 4274 putative protein coding sequences, 126 tRNA genes and 34 rRNA genes. Furthermore, we found 33 type III secretion system 1 (T3SS1) related proteins and 15 type III secretion system 2 (T3SS2) related proteins on chromosome 1. This is the first reported result of Type III secretion system 2 located on chromosome 1 of V. parahaemolyticus without thermostable direct hemolysin (tdh) and thermostable direct hemolysin-related hemolysin (trh).ConclusionsThrough investigation of the complete genome sequence of V. parahaemolyticus FORC_014, which differs from previously reported strains, we revealed two type III secretion systems (T3SS1, T3SS2) located on chromosome 1 which do not include tdh and trh genes. We also identified several virulence factors carried by our strain, including iron uptake system, hemolysin and secretion system. This result suggests that the FORC_014 strain may be one pathogen responsible for foodborne illness outbreak. Our results provide significant genomic clues which will assist in future understanding of virulence at the genomic level and help distinguish between clinical and non-clinical isolates.Electronic supplementary materialThe online version of this article (doi:10.1186/s13099-016-0134-0) contains supplementary material, which is available to authorized users.

Vibrio parahaemolyticusis a Gram-negative halophilic bacterium that causes food-borne gastroenteritis in humans who consumeV. parahaemolyticus-contaminated seafood.The FORC_023 strain was isolated from raw fish storage water, containing live fish at a sashimi restaurant. Here, we aimed to sequence and characterize the genome of the FORC_023 strain. The genome of the FORC_023 strain showed two circular chromosomes, which contained 4227 open reading frames (ORFs), 131 tRNA genes and 37 rRNA genes. Although the genome of FORC_023 did not include major virulence genes, such as genes encoding thermostable direct hemolysin (TDH) and TDH-related hemolysin (TRH), it contained genes encoding other hemolysins, secretion systems, iron uptake-related proteins and severalV. parahaemolyticusislands. The highest average nucleotide identity value was obtained between the FORC_023 strain and UCM-V493 (CP007004-6). Comparative genomic analysis of FORC_023 with UCM-V493 revealed that FORC_023 carried an additional genomic region encoding virulence factors, such as repeats-in-toxin and type II secretion factors. Furthermore,in vitrocytotoxicity testing showed that FORC_023 exhibited a high level of cytotoxicity toward INT-407 human epithelial cells. These results suggested that the FORC_023 strain may be a food-borne pathogen.