Multilocus Sequence Analysis of the redefined clade Scophthalmi in the genus Vibrio

A Multilocus Sequence Analysis (MLSA) was performed on members of the Scophthalmi clade in the genus Vibrio, including type and reference strains of the species V. scophthalmi, V. ichthyoenteri, and 39 strains phenotypically identified as Vibrio ichthyoenteri-like, with the aim of better defining boundaries between these two closely related, fish-associated species. The type strain of V. ponticus, recently added to the clade Scophthalmi, was also included. The study was based on partial sequences of the protein-coding housekeeping genes rpoD, mreB, recA, ftsZ, and gyrB, and the 16S rRNA. While the 16S rRNA gene-based trees were unable to pull apart members of V. scophthalmi or V. ichthyoenteri, both the other individual gene trees and the trees obtained from the five-genes concatenated sequences were able to consistently differentiate four subclades within the main clade, corresponding to the bona fide V. scophthalmi, V. ichthyoenteri, and two small ones that may represent a new species each. The best genes to differentiate V. scophthalmi from V. ichthyoenteri were rpoD, recA, and mreB. Vibrio ponticus failed to associate to the clade in the MLSA and in most single gene trees for which it should not be considered part of it. In this study we also confirm using genomic indexes that V. ichthyoenteri and V. scophthalmi are two separate species.