Evidence for a natural gene transfer from the ponyfish to its bioluminescent bacterial symbiont Photobacter leiognathi. The close relationship between bacteriocuprein and the copper-zinc superoxide dismutase of teleost fishes.

The copper and zinc-containing superoxide dismutases of six teleost fish species and of the bioluminescent bacterium Photobacter leiognathi were isolated and characterized, as was the iron-containing superoxide dismutase of P. leiognathiThe amino acid composition of the CuZn enzyme from P. leiognathi was more closely related to the corresponding fish enzymes than it was to any other yet described CuZn superoxide dismutase.Rank order correlation analysis o f amino acid difference indices, computed for all pairwise comparisons of bacteriocuprein and the ponyfish enzyme with other CuZn-superoxide dismutases, suggested that the bacterid and ponytish enzymes occupy similar phylogenetic positions, being most closely related to the superoxide dismutases of teleost fish.Discriminant functions analysis of all available superoxide dismutase amino acid compositions demonstrated that correct group classification could be achieved on the sole basis of amino acid composition.Thus, Fe and Mn superoxide dismutase groups could be delineated and both groups differed dramatically from the CuZn-superoxide dismutases, Bacteriocuprein was classified with the CuZn-superoxide dismutase group.Moreover, this analytical method subdivided the CuZn group into three subgroups made up of the avian plus mammalian, plant plus fungal, and the fish enzymes, with the P. €eeiognuthi enzyme placed in the fish subgroup.The physicochemical properties of the P. leiognuthi CuZn-superoxide dismutases were very similar to those of the comparable CuZn enzymes from other sources, especially those of teleost fish.In view of the long standing symbiosis between P.Zeiognathi and its teleost hosts, the leiognathid fishes, these results suggest that the gene specifying the CuZnsuperoxide dismutase was transferred from the fish to the bacterium, during their coevolutionary history.Three major types of superoxide dismutases have been described.The first of these contains Cu and Zn, the second