An MLSA approach for the taxonomic update of the Splendidus clade, a lineage containing several fish and shellfish pathogenic Vibrio spp.

A multilocus sequence analysis was undertaken in order to redefine the Splendidus clade of the genus Vibrio, a large group of species containing several pathogenic members that affect fish and shellfish, and are difficult to identify through both phenotypic and genotypic approaches. The study included analysis of partial sequences of recA, gyrB, mreB, rpoD and pyrH genes, as well as the 16S rRNA gene. Seventeen type strain species were included that were complemented with other reference strains and a collection of isolates tentatively identified as members of this clade, as well as a set of other Vibrio species. The clade was well defined and stable in all analyses, and was confirmed to contain V. celticus, V. atlanticus, V. artabrorum, V. toranzoniae and V. hemicentroti, in addition to the twelve previously recognized species. While some species were well-defined members (e.g. Vibrio cyclitrophicus, V. chagasii) others formed tight groups that were related by sequence similarities and lineage topology, which suggested a synonymy among their members, particularly the V. splendidus-V. hemicentroti pair. Most of the isolates were related to two major groups: the V. celticus-V. crassostreae-V. gigantis subclade that contained all isolates from oysters sampled in the cold season, and V. chagasii that included oyster isolates from warm months. This suggested a sharp seasonal occurrence for these species. None of the single genes were able to mimic the resolving power of the five-gene MLSA and none worked well for the identification of the whole group of species in the clade.