Isocitrate Dehydrogenase Mutation in \u3ci\u3eVibrio anguillarum\u3c/i\u3e Results in Virulence Attenuation and Immunoprotection in Rainbow Trout (\u3ci\u3eOncorhynchus mykiss\u3c/i\u3e)

Background Vibrio anguillarum is an extracellular bacterial pathogen that is a causative agent of vibriosis in finfish and crustaceans with mortality rates ranging from 30% to 100%. Mutations in central metabolism (glycolysis and the TCA cycle) of intracellular pathogens often result in attenuated virulence due to depletion of required metabolic intermediates; however, it was not known whether mutations in central metabolism would affect virulence in an extracellular pathogen such as V. anguillarum. Results Seven central metabolism mutants were created and characterized with regard to growth in minimal and complex media, expression of virulence genes, and virulence in juvenile rainbow trout (Oncorhynchus mykiss). Only the isocitrate dehydrogenase (icd) mutant was attenuated in virulence against rainbow trout challenged by either intraperitoneal injection or immersion. Further, the icd mutant was shown to be immunoprotective against wild type V. anguillarum infection. There was no significant decrease in the expression of the three hemolysin genes detected by qRT-PCR. Additionally, only the icd mutant exhibited a significantly decreased growth yield in complex media. Growth yield was directly related to the abundance of glutamate. A strain with a restored wild type icd gene was created and shown to restore growth to a wild type cell density in complex media and pathogenicity in rainbow trout. Conclusions The data strongly suggest that a decreased growth yield, resulting from the inability to synthesize α-ketoglutarate, caused the attenuation despite normal levels of expression of virulence genes. Therefore, the ability of an extracellular pathogen to cause disease is dependent upon the availability of host-supplied nutrients for growth. Additionally, a live vaccine strain could be created from an icd deletion strain

H-NS Is a Negative Regulator of the Two Hemolysin/Cytotoxin Gene Clusters in \u3cem\u3eVibrio anguillarum\u3c/em\u3e

Hemolysins produced by Vibrio anguillarum have been implicated in the development of hemorrhagic septicemia during vibriosis, a fatal fish disease. Previously, two hemolysin gene clusters responsible for the hemolysis and cytotoxicity of V. anguillarum were identified: the vah1-plp gene cluster and the rtxACHBDE gene cluster. In this study, we identified the hns gene, which encodes the H-NS protein and acts as a negative regulator of both gene clusters. The V. anguillarum H-NS protein shares strong homology with other bacterial H-NS proteins. An hns mutant exhibited increased hemolytic activity and cytotoxicity compared to the wild-type strain. Complementation of the hns mutation restored hemolytic activity and cytotoxicity levels to nearly wild-type levels. Furthermore, expression of rtxA, rtxH, rtxB, vah1, and plp increased in the hns mutant and decreased in the hns-complemented mutant strain compared to expression in the wild-type strain. Additionally, experiments using DNase I showed that purified recombinant H-NS protected multiple sites in the promoter regions of both gene clusters. The hns mutant also exhibited significantly attenuated virulence against rainbow trout. Complementation of the hns mutation restored virulence to wild-type levels, suggesting that H-NS regulates many genes that affect fitness and virulence. Previously, we showed that HlyU is a positive regulator of expression for both gene clusters. In this study, we demonstrate that upregulation by hlyU is hns dependent, suggesting that H-NS acts to repress or silence both gene clusters and HlyU acts to relieve that repression or silencing

Draft Genome Sequence of the Marine Pathogen \u3cem\u3eVibrio coralliilyticus\u3c/em\u3e RE22

Vibrio coralliilyticus RE22 is a causative agent of vibriosis in larval bivalves. We report here the draft genome sequence of V. coralliilyticus RE22 and describe additional virulence factors that may provide insight into its mechanism of pathogenicity

Draft Genome Sequence of the Shellfish Larval Probiotic Bacillus pumilus RI06-95

Bacillus pumilus RI06-95 is a marine bacterium isolated in Narragansett, Rhode Island, which has shown probiotic activity against marine pathogens in larval shellfish. We report the genome of B. pumilus RI06-95, which provides insight into the microbe’s probiotic ability and may be used in future studies of the probiotic mechanism

Draft Genome Sequence of Aliiroseovarius crassostreae CV919-312, the Causative Agent of Roseovarius Oyster Disease (Formerly Juvenile Oyster Disease)

Aliiroseovarius crassostreae CV919-312 is a marine alphaproteobacterium and the causative agent of Roseovarius oyster disease. We announce here the draft genome sequence of A. crassostreae CV919-312 and identify potential virulence genes involved in pathogenicity

Draft Genome Sequence of the Emerging Bivalve Pathogen \u3cem\u3eVibrio tubiashii\u3c/em\u3e subsp. \u3cem\u3eeuropaeus\u3c/em\u3e

Vibrio tubiashii subsp. europaeus is a bivalve pathogen isolated during episodes of mortality affecting larval cultures in different shellfish hatcheries. Here, we announce the draft genome sequence of the type strain PP-638 and describe potential virulence factors, which may provide insight into the mechanism of pathogenicity

Draft Genome Sequence of Loktanella Maritima Strain YPC211, a Commensal Bacterium of the American Lobster (\u3cem\u3eHomarus Americanus\u3c/em\u3e)

Loktanella maritima strain YPC211 was isolated from the American lobster (Homarus americanus). We report here the draft genome sequence for L. maritima YPC211 and identify genes of potential importance to its role within the microbial community

Draft Genome Sequence of the New Pathogen for Bivalve Larvae \u3cem\u3eVibrio bivalvicida\u3c/em\u3e

Vibrio bivalvicida is a novel pathogen of bivalve larvae responsible for recent vibriosis outbreaks affecting shellfish hatcheries. Here, we announce the draft genome sequence of V. bivalvicida 605 and describe potential virulence factors

Draft Genome Sequence of Bowmanella denitrificans JL63, a Bacterium Isolated from Whiteleg Shrimp (\u3cem\u3eLitopenaeus vannamei\u3c/em\u3e) That Can Inhibit the Growth of Vibrio Parahaemolyticus

Bowmanella denitrificans strain JL63 was isolated from a whiteleg shrimp (Litopenaeus vannamei) and was determined to have antibacterial activity against an acute hepatopancreatic necrosis disease (AHPND) strain of Vibrio parahaemolyticus. Here, we report the draft genome sequence of this strain and identify genes that are potentially involved in its antibacterial activity