Multilocus Sequence Analysis of Close Relatives Vibrio anguillarum and Vibrio ordalii

• Published in: Applied and Environmental Microbiology
• Main Authors: Steinum, Terje M., Karataş, Süheyla, Martinussen, Nora Tandstad, Meirelles, Pedro M., Thompson, Fabiano L., Colquhoun, Duncan J.
• Other Authors: Björkroth, J.
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Society for Microbiology 2016
• Subjects: atlantic cod
• Online Access: http://dx.doi.org/10.1128/aem.00620-16; https://journals.asm.org/doi/pdf/10.1128/AEM.00620-16

ABSTRACT The genetic heterogeneity of the close relatives Vibrio anguillarum and Vibrio ordalii , both serious pathogens of fish causing extensive losses in aquaculture, was studied. Eight housekeeping genes, i.e., atpA , ftsZ , gapA , gyrB , mreB , rpoA , topA , and pyrH , were partially sequenced in 116 isolates from diverse fish species and geographical areas. The eight genes appear to be under purifying selection, and the genetic diversity in the total data set was estimated to be 0.767 ± 0.026. Our multilocus sequence analysis (MLSA) scheme identified several widespread clonal complexes and resolved the isolates, for the most part, according to serotype. Serotype O2b isolates from diseased cod in Norway, Ireland, and Scotland were found to be extremely homogeneous. Horizontal gene transfer appears to be fairly common within and between clonal complexes. Taken together, MLSA and in silico DNA-DNA hybridization (DDH) calculations suggest that some isolates previously characterized as V . ordalii , i.e., 12B09, FF93, FS144, and FS238, are in fact V. anguillarum isolates. The precise taxonomic situation for two isolates from Atlantic cod that display several traits consistent with V. ordalii , i.e., NVI 5286 and NVI 5918, and a single environmental strain that was previously considered to represent V. ordalii , i.e., FF167, is less clear. IMPORTANCE It is still being debated whether V. anguillarum and V . ordalii represent separate bacterial species. Our study addresses this issue and elucidates the degree of genetic variability within this group of closely related bacteria, based on a substantial number of isolates. Our results clearly illustrate the existence of different populations among putative V . ordalii isolates. On the basis of additional full-length genomic analysis, we conclude that most environmental isolates previously identified as V . ordalii lie firmly within the species V. anguillarum . While bona fide fish-pathogenic V . ordalii isolates display a very close genetic relationship with V. ...