Drug Discovery in Exotic Marine Symbionts

Rare and exotic marine organisms have proven to be a promising source of new drugs and other bioactive compounds. Haygood and collaborators have discovered that giant shipworms and other mollusks harbor a rich ecosystem of symbiotic bacteria, and that the symbiotic relationships between marine bacteria and marine animals are based on chemical signals exchanged between mollusks, for instance, and their bacterial symbionts. The discoveries garnered significant attention owing to their potential for providing rich platforms for drug discovery. The "wooden-steps" hypothesis proposed that large chemosynthetic mussels found at deep-sea hydrothermal vents descend from much smaller species associated with sunken wood and other organic deposits and that the endosymbionts of these progenitors made use of hydrogen sulfide from biogenic sources (e.g., decaying wood) rather than from vent fluids. The study of bacterial symbiosis in exotic organisms, such as shipworm mollusks, illustrates universal principles that may be applied to the human microbiome

Phylogenetic resolution and habitat specificity of members of the Photobacterium phosphoreum species group

Substantial ambiguity exists regarding the phylogenetic status of facultatively psychrophilic luminous bacteria identified as Photobacterium phosphoreum , a species thought to be widely distributed in the world's oceans and believed to be the specific bioluminescent light-organ symbiont of several deep-sea fishes. Members of the P. phosphoreum species group include luminous and non-luminous strains identified phenotypically from a variety of different habitats as well as phylogenetically defined lineages that appear to be evolutionarily distinct. To resolve this ambiguity and to begin developing a meaningful knowledge of the geographic distributions, habitats and symbiotic relationships of bacteria in the P. phosphoreum species group, we carried out a multilocus, fine-scale phylogenetic analysis based on sequences  of  the  16S  rRNA,  gyrB  and  luxABFE   genes of many newly isolated luminous strains from symbiotic and saprophytic habitats, together with previously isolated luminous and non-luminous strains identified as P. phosphoreum from these and other habitats. Parsimony analysis unambiguously resolved three evolutionarily distinct clades, phosphoreum , iliopiscarium and kishitanii . The tight phylogenetic clustering within these clades and the distinct separation between them indicates they are different species, P. phosphoreum , Photobacterium iliopiscarium and the newly recognized ‘Photobacterium kishitanii’ . Previously reported non-luminous strains, which had been identified phenotypically as P. phosphoreum , resolved unambiguously as P. iliopiscarium , and all examined deep-sea fishes (specimens of families Chlorophthalmidae, Macrouridae, Moridae, Trachichthyidae and Acropomatidae) were found to harbour ‘P. kishitanii’ , not P. phosphoreum , in their light organs. This resolution revealed also that ‘P. kishitanii’ is cosmopolitan in its geographic distribution. Furthermore, the lack of phylogenetic variation within ‘P. kishitanii’ indicates that this facultatively symbiotic bacterium is not cospeciating with its phylogenetically divergent host fishes. The results of this fine-scale phylogenetic analysis support the emerging view that bacterial species names should designate singular historical entities, i.e. discrete lineages diagnosed by a significant divergence of shared derived nucleotide characters.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74443/1/j.1462-2920.2005.00859.x.pd