Complete Genome Sequence of the Marine Fish Pathogen Vibrio anguillarum Harboring the pJM1 Virulence Plasmid and Genomic Comparison with Other Virulent Strains of V. anguillarum and V. ordalii

Abstract

We dissected the complete genome sequence of the O1 serotype strain Vibrio anguillarum 775(pJM1) and determined the draft genomic sequences of plasmidless strains of serotype O1 (strain 96F) and O2␤ (strain RV22) and V. ordalii. All strains harbor two chromosomes, but 775 also harbors the virulence plasmid pJM1, which carries the anguibactin-producing and cognate transport genes, one of the main virulence factors of V. anguillarum. Genomic analysis identified eight genomic islands in chromosome 1 of V. anguillarum 775(pJM1) and two in chromosome 2. Some of them carried potential virulence genes for the biosynthesis of O antigens, hemolysins, and exonucleases as well as others for sugar transport and metabolism. The majority of genes for essential cell functions and pathogenicity are located on chromosome 1. In contrast, chromosome 2 contains a larger fraction (59%) of hypothetical genes than does chromosome 1 (42%). Chromosome 2 also harbors a superintegron, as well as host "addiction" genes that are typically found on plasmids. Unique distinctive properties include homologues of type III secretion system genes in 96F, homologues of V. cholerae zot and ace toxin genes in RV22, and the biofilm formation syp genes in V. ordalii. Mobile genetic elements, some of them possibly originated in the pJM1 plasmid, were very abundant in 775, resulting in the silencing of specific genes, with only few insertions in the 96F and RV22 chromosomes.Vibrio anguillarum is a marine pathogen that causes vibriosis in close to 50 species of fish, including cultured and wild fish, mollusks, and crustaceans, in marine, brackish, and fresh water (1). Vibriosis is a hemorrhagic septicemia with dire consequences for fish rearing, especially in countries that depend heavily on fish for their food consumption. Despite the fact that V. anguillarum is a dramatic cause of vibriosis in fish, little is known about the genomic composition of this important pathogen. Although 23 serotypes have been reported in V. anguillarum, the O1 and O2 serotypes are the major causative agent of fish vibriosis (32,66,75). Many O1 serotype strains harbor 65-kb pJM1-type plasmids, which carry the siderophore anguibactin biosynthesis and transport genes, a main virulence factor of V. anguillarum, while one of the O1 serotype strains and other serotypes, such as all of the O2 strains, are plasmidless (1, 13, 33, 76). Many virulence factors have been characterized, but we are still far from getting the whole picture of the virulence mechanisms of this pathogen (1, 50). The fact that the pJM1 plasmid is an important component of virulence for the 775 strain but that the other three strains examined do not harbor this plasmid and are still virulent indicates that they must have different mechanisms to cause disease. Moreover, O1 serotype strains cause disease in salmonid fish, whereas O2␤ strains are usually isolated from cod and other nonsalmonids (1, 32, 43). We have previously performed random genome sequencing of V. anguillarum 775 genomic DNA and identified potent...

H-NS Is a Negative Regulator of the Two Hemolysin/Cytotoxin Gene Clusters in Vibrio anguillarum

“…The results of this examination revealed that the GC content of the rtxACHBDE gene cluster is 47.3% and the GC content of the vah1-plp gene cluster is 42.5%. Both values are very similar to the average GC content of the whole genome (44.51%) of V. anguillarum (28). The intergenic regions do have low GC/elevated AT percentages, with the plp-vah1 intergenic region having 26% GC and the rtxB-rtxH region having 28% GC (Fig.…”

Survival behaviour and virulence of the fish pathogen Vibrio ordalii in seawater microcosms

“…V. ordalii is able to form biofilm, adhere to glass surfaces coated with fish mucus and possesses a hydrophobic character, which could be relevant in the marine aquatic environment to facilitate survival, colonization and host invasion (Ruiz et al 2015). This result is in accordance with that described by Naka et al (2011), whereby the V. ordalii type strain carries the syp genes involved in biofilm formation.…”

Cell-surface properties of Vibrio ordalii strains isolated from Atlantic salmon Salmo salar in Chilean farms

“…Other factors are the ability of this pathogen to resist the bactericidal action of fish serum ) and to agglutinate different eukaryotic cell types, suggesting that V. ordalii attaches to and interacts with the host cells (Larsen & Mellergaard 1984). More recently, in the strain ATCC 33509 T genome, Naka et al (2011) identified biosynthesis and transport genes for a yersi niabactin-like siderophore, which could play a role in virulence. In addition, in the same strain, all hemolysin genes were conserved except for vah4, and an entire biofilm formation cluster was identified: the Syp system, except for SypE, a negative regulator.…”