Phylogenetic relationships between species in the genus Photobacterium have been
poorly studied despite pathogenic and ecological relevance of some of its members. This is the
first phylogenetic study that includes new species of Photobacterium (validated or not) that have
not been included in any of the previously described clades, using 16S rRNA sequences and
multilocus sequence analysis (MLSA) in concatenated sequences of gyrB, gapA, topA, ftsZ and
mreB housekeeping genes. Sequence analysis has been implemented using Maximum-parsimony
(MP), Neighbour-joining (NJ) and Maximum likelihood (ML) treeing methods and the predicted
evolutionary relationship between the Photobacterium clades was established on the basis of bootstrap
values of >75% for 16S rRNA sequences and MLSA. We have grouped 22 species of the genus
Photobacterium into the following 5 clades: Phosphoreum (comprises P. aquimaris, “P. carnosum,”
P. iliopiscarium, P. kishitanii, P. phosphoreum, “P. piscicola” and “P. toruni”); clade Profundum (composed
of P. aestuarii, P. alginatilyticum, P. frigidiphilum, P. indicum, P. jeanii, P. lipolyticum, “P. marinum,” and
P. profundum); clade Damselae (two subspecies of P. damselae, damselae and piscicida); and two new
clades: clade Ganghwense (includes P. aphoticum, P. aquae, P. galatheae, P. ganghwense, P. halotolerans,
P. panuliri and P. proteolyticum); and clade Leiognathi (composed by P. angustum, P. leiognathi subsp.
leiognathi and “P. leiognathi subsp. mandapamensis”). Two additional clades, Rosenbergii and Swingsii,
were formed using a phylogenetic method based on 16S rRNA gene, although they are not confirmed
by any MLSA methods. Only P. aplysiae could not be included in none of the established clade,
constituting an orphan clade.
