Phylogeny, genomics, and symbiosis of Photobacterium (original) (raw)

2011, FEMS Microbiology Reviews

Photobacterium comprises several species in Vibrionaceae, a large family of Gramnegative, facultatively aerobic, bacteria that commonly associate with marine animals. Members of the genus are widely distributed in the marine environment and occur in seawater, surfaces, and intestines of marine animals, marine sediments and saline lake water, and light organs of fish. Seven Photobacterium species are luminous via the activity of the lux genes, luxCDABEG. Much recent progress has been made on the phylogeny, genomics, and symbiosis of Photobacterium. Phylogenetic analysis demonstrates a robust separation between Photobacterium and its close relatives, Aliivibrio and Vibrio, and reveals the presence of two well-supported clades. Clade 1 contains luminous and symbiotic species and one species with no luminous members, and Clade 2 contains mostly nonluminous species. The genomes of Photobacterium are similar in size, structure, and organization to other members of Vibrionaceae, with two chromosomes of unequal size and multiple rrn operons. Many species of marine fish form bioluminescent symbioses with three Photobacterium species: Photobacterium kishitanii, Photobacterium leiognathi, and Photobacterium mandapamensis. These associations are highly, but not strictly species specific, and they do not exhibit symbiont-host codivergence. Environmental congruence instead of host selection might explain the patterns of symbiont-host affiliation observed from nature. The currently recognized species of Photobacterium (January 2010) are listed in Table 1. Members of the genus, collectively and individually, are widely distributed geographically in the marine environment and have been isolated from seawater at many locations, from the skin, intestines, and intestinal tracts of marine animals, from stored fish tissue, from marine corals, from light organs of many species of marine fish, and from marine sediments and saline lake water (Table 1). Environmental distributions are known to some extent for some species; for example, Photobacterium leiognathi is found more commonly in coastal, warmer waters and in bioluminescent