DNA Homology and Taxonomy of Pseudomonas and Xanthomonas

Abstract

SUMMARYThe relatedness between several nomen species of the PseudomonasXanthomonas group and some other organisms was numerically fixed through D N A homology and D N A base composition. For Pseudomonas the numerically analysed strains proposed by Lysenko as neotypes were used. The mean Yo (G+C) was in the range 60-67.5. 14C-DNA from either Fseudomonasfluorescens or P. putida was hybridized with D N A from 17 different species centres and the D N A homology was in the range 50-100 %.Genetic species differentiation in the genus Pseudomonas seems justified. In three border cases (P. iodinum, P. diminuta and P. atlantica) D N A homology was only 28-50%, so the inclusion of these organisms in the genus Pseudomonas is uncertain. The species centres P. pavonacea and F. rubescens are omitted from the genus Pseudomonas because of their very low D N A homology and aberrant D N A base composition. Twentyeight nomen species of Xanthomonas all form a narrow group in the range 63.5-69y0 (G+C). With two exceptions D N A homology with a median strain Xanthomonas pelargonii was always over 75 yo and frequently nearly complete. 14C-DNA from P. fluorescens hybridized with Xanthomomas-DNA to the same extent as with the pseudomonads proper. The Xanthomonas cluster overlapped perfectly with part of the Pseudomonas group. It is proposed therefore to gather all xanthomonads in a single genetic species P. campestris. This is such a dense cluster that the preservation of separate species names for the border cases seems undesirable. About one half to two-thirds of Pseudomonas-and Xanthomolzas-DNA is identical. The genera Rhixobium, Axotobacter and Axomonas appeared to be rather closely related to Pseudomonas since they shared some 40-50y0 of their DNA. The genus Serratia appeared to be more closely related to Pseudomonas than to Escherichia. The genera Gluconobacter, Acetobacter, Serratia and Escherichia shared some 20-30y0 D N A with Pseudomonas, but Bacillus-DNA was almost entirely different. From a comparison between D N A homology and taximetric similarity, it appeared that most pseudomonads would not contain unused genes. The advantages of a classification based on % (G+C) and D N A homology are obvious.

Taxonomic Study of Bacillus by Deoxyribonucleic Acid-Deoxyribonucleic Acid Hybridization and Interspecific Transformation

“…According to these authors, the homology indexes between different strains of E. coli and between several species of Shigella, Salmonella, and Alkalescens-Dispar and E. coli were from 100 to 36%, more than 70, 45, and 88%, respectively, measured by the hydroxapatite binding method. De Ley et al (6) also reported high homology indexes in Pseudomonas (100 to 55%), except two strains which showed low homology indexes (5%), and Xanthomonas (100 to 54%) by interspecific DNA-DNA hybridization.…”

Notes on the characterization of prokaryote strains for taxonomic purposes

“…The technique of DNA-DNA or DNA-RNA hybridization was introduced into prokaryote systematics from the 1960s onwards (Brenner et al, 1967;De Ley et al, 1966;Johnson & Ordal, 1968;McCarthy & Bolton, 1963;Pace & Campbell, 1971;Palleroni et al, 1973 T m is calculated on the basis of the known DNA G+C content of the strains to be hybridized. The temperature at which the hybridization is carried out must be clearly stated.…”

Deoxyribonucleic Acid Homology in Yeasts. Genetic Relatedness within the Genus Candida

“…The use of nucleic acid homology techniques has proved valuable in determining genetic relatedness among micro-organisms including various bacteria (Weissman, Reich, Somerson & Cole, 1966;De Ley, Park, Tijtgat & van Ermengem, 1966) and mycoplasmas . One of the methods for determining DNA-RNA hybrid formation is the technique described by Gillespie & Spiegelman (1965).…”