Abstract
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.
Highlights
The family Vibrionaceae (Gammaproteobacteria) is a diverse group of Gram-negative bacteria that includes following genera: Vibrio, Photobacterium, Aliivibrio, Catenococcus, Echinomonas, Enterovibrio, Grimontia and Salinivibrio [1,2]
According to the biochemical and physiological profiles, 15 strains belong to P. damselae subsp. damselae and 3 strains were classified as P. damselae subsp. piscicida
The intraspecific variation among P. damselae subsp. damselae strains was recorded for the following characteristics: lysine decarboxylase, acetoine production, amylase, gelatinase, lipase and haemolysin production; whilst, for P. damselae subsp. piscicida strains the intraspecific variation was obtained for acetoine production, amylase and acids from L-arabinose (Supplementary Table S3)
Summary
The family Vibrionaceae (Gammaproteobacteria) is a diverse group of Gram-negative bacteria that includes following genera: Vibrio, Photobacterium, Aliivibrio, Catenococcus, Echinomonas, Enterovibrio, Grimontia and Salinivibrio [1,2]. Photobacterium species display varied phenotypic, physiological and ecological characteristics, all of them are chemoorganotrophs, possess Q-8 as the predominant respiratory lipoquinone and present C16:1 and C16:0 as their major fatty acids. This genus has been revised on the basis of its taxonomic, ecological and pathogenic characteristics [4]. P. damselae [8] was formed as a new combination for former Vibrio damsela and Pasteurella piscicida. This species is the only one for which subspecies have been proposed so far with the publication of P. damselae subsp. In the last two decades, the number of descriptions has intensified with the proposal of 24 novel species and two new combinations with valid names (Table 1)
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