Study of genetic relationships among marine species of the genera Beneckea and Photobacterium by means of in vitro DNA/DNA hybridization

Abstract

Strains representative of species of the marine genera Beneckea and Photobacterium were used as reference standards in in vitro DNA/DNA competition experiments. Within a given species, strains were found to be related by over 80% competition. (Competition was defined as the amount of radioactive DNA displaced by heterologous DNA relative to the amount displaced by homologous DNA.) On the basis of interspecies competition values (expressed as averages), the following groupings could be made: 1. "Photobacterium" fischeri was related to strain ATCC 15382 by a competition of 38% and was distinct from all the other strains tested (competition less than or equal to 11%). 2. The genus Photobacterium consisted of 3 species, P.phosphoreum, P.leiognathi, and a newly designated species, P.angustum (composed of non-luminous strains). The latter species was found to be related to P.leiognathi and P.phosphoreum by 56 and 28% competition, respectively, while P.phosphoreum was related to P.leiognathi by 29%. 3. In the genus Beneckea, 65% competition was detected between B.harveyi and B.campbellii as well as between B.parahaemolytica and B.alginolytica. These pairs of species were related to each other by 51-58% and to B.natriegens by 34-56% competition. A newly designated pathogenic species, B.vulnifica, appeared to have a low but significant relationship to all the above mentioned species of Beneckea. 4. Two biotypes, related by 68% competition, were recognized in the species B.splendida. Similarly, B.pelagia was found to consist of 2 biotypes related by a competition of 67%. The competition values between these species were 38-40%. 5. B.nereida, B.nigrapulchrituda, and "Vibrio" anguillarum had competition values less than or equal to 30% to each other as well as to other species of Beneckea. 6. With Vibrio cholerae as the reference standard, V.albensis was found to be related by a competition of 82%, while V.proteus and V.metschnikovii had competition values of 22 and 12%, respectively. These results suggested that V.albensis should be synonymized with V.cholerae, while the latter two organisms should remain distinct from this species. V.cholerae as well as the other terrestrial organisms tested did not appear to be significantly related to any of the marine strains (competition values less than or equal to 27%). The speciation derived from the results of the DNA/DNA competition experiments was compared to previous speciation based on phenotypic similarities.

Evaluation of the Genus Listonella and Reassignment of Listonella damsela (Love et al.) MacDonell and Colwell to the Genus Photobacterium as Photobacterium damsela comb. nov. with an Emended Description

“…anguillarum and L . pelagia have exhibited at least 20 to 30% DNA homology (under optimal conditions) with most other Vibrio species tested in previous studies (12,33). This level is considered by some authors to be appropriate for members of the one genus (34).…”

“…Similarly, Vibrio cholerae and Vibrio mimicus, which are also closely related as determined by DNA homology levels (40 to 67% at 63°C [15] and 55 to 67% at 60°C [12]), also failed to cluster in the 5s rRNA analysis (23). In contrast, Photobacterium leiognathi and Photobacterium angustum, which exhibited levels of DNA homology similar to those described above (53 to 61% at 63°C [33]), were found to have identical 5s rRNA sequences (23).…”

“…Vibrio harveyi was closely related to Vibrio alginolyticus and Vibrio parahuemolyticus as measured by levels of DNA homology (50 to 58% at 63°C [33] and 52 to 55% at 60°C [12]). but V .…”

“…Such levels provide no indication of a close relationship, and it has been suggested that these two species may deserve a separate generic designation (5,32,33).…”

Vibrio rotiferianus sp. nov., isolated from cultures of the rotifer Brachionus plicatilis

“…(Reichelt et al, 1976), and later called the core group of the Vibrio genus (Dorsch et al, 1992). This group has had little taxonomic change over time; the last species described was Vibrio vulnificus (Farmer, 1980).…”