No abstract

On the basis of ribosomal ribonucleic acid homologies, the genus Pseudomonas can be divided into at least five distinct groups, some of which are as distantly related t o each other as they are to Escherichia coli. One of these groups contains members of the genus Xanthomonas. The data presented support and extend the previous grouping based on deoxyribonucleic acid homologies and support the current view that the portion of the genome coding for ribosomal ribonucleic acid is more conserved in the course of evolution than the bulk of the genome.For about nine years our laboratory has been largely involved in taxonomic studies of the genus Pseudomonas. Our first approach was the phenotypic characterization of a large number of strains using mainly nutritional characters. On the basis of phenotypic resemblance, we recognized several "species groups," comprised of what we regarded as recognizable species. Below the specific rank, we further recognized a number of "biotypes," some of which had been previously described as species, and many of which may deserve specific rank (14). Deoxyribonucleic acid (DNA)-DNA hybridization experiments generally supported our conclusions based on phenotypic data but showed that some of the species and biotypes were quite heterogeneous with respect to DNA homology. It was also found that some species groups were sufficiently closely related to each other t o be united in a larger DNA homology complex. For example, the "P. fluorescens complex" was found to contain not only the "fluorescent group" but also the nonfluorescent pseudomonads that had been assigned to the "alcaligenes" and "stutzeri" groups ( 10, 14). Our studies have been reviewed recently (9).To pursue further our studies on bacterial phylogeny and speciation, we have resorted to ribosomal ribonucleic acid (rRNA)-DNA hybridizations among selected members of the various DNA homology groups, and included three species of Xanthomonas in the studies. The results are reported in the present paper. MATERIALS AND METHODSBacterial strains. The bacterial strains used in the presently described experiments are numbered as in our previous publications (1,2,4,7,8,(10)(11)(12)14). Reparation of rRNA. For the preparation of unlabeled rRNA, most strains were grown in a medium containing 0.033 M K-Na phosphate buffer, pH 6.8; (NH,), SO,, 0.1%; asparagine, 0.2%; yeast extract, 0.5%; Hutner mineral base (3), 10 ml per liter. For the growth of P. rnaltophilia, DL-sodium lactate was substituted for asparagine. P. saccharophila was grown in a medium containing 0.033 M K-Na phosphate buffer, pH 6.8; NH,Cl, 0.1%; MgSO, 07 H,O, 0.05%; ferric ammonium citrate, 0.005%; CaCl, , 0.0005%; and sodium succinate, 0.2%. For the growth of P. diminuta, the same basal medium was used as for P. saccharophila except that succinate was replaced by asparagine and the essential growth factors (1) were added. The cultures were grown at 30 C on a rotary shaker. The cells were suspended in 0.02 M tris-(hydroxymethy1)aminomethane (Tris)-hydrochloride buffer, pH 7....

No abstract

A number of nutritional and biochemical properties of more than 100 strains of the oxidase-negative moraxellas (the Mima-Herellea-Acinetobacter group of bacteria) were studied. These properties included the range of carbon sources that can support growth, the utilization of nitrate, the production of proteolytic and lipolytic enzymes, and the reactions involved in the oxidation of sugars and of aromatic compounds. No evidence could be obtained for the accumulation of either poly-3-hydroxybutyrate or polysaccharide as intracellular reserve materials. Of 158 different compounds tested, the group as a whole could use 85 as sole carbon sources for growth. The nutritional spectra of the individual strains, however, differed widely, with a range of from 17 to 74 alternative substrates. On the basis of 56 selected nutritional and physiological characters used for a numerical analysis, the collection could be divided into two major groups of strains comprising at least seven less clearly defined clusters. Neither the hydrolysis of gelatin nor acid production from aldose sugars was found to be a reliable index of strain affinities indicated by the phenotypic analysis, although both properties were of some use in distinguishing between the subgroups. For reasons that are discussed, we propose that the oxidasenegative moraxellas be placed in the genus Acinetobacter Brisou and Prevot, for which a modified description is presented. A. calco-aceticus (Beijerinck) is proposed as the type species, of which anitratum is regarded as a synonym or variety. On the basis of the present studies and unpublished supporting evidence provided by M. Mandel on deoxyribonucleic acid (DNA) composition and by J. Johnson on DNA homologies, it is proposed that two other species in the genus, A. lwoffi (Audureau) and A. hemolysans (Henriksen), as well as one subspecies, A. hemolysans haemolyticus (Stenzel and Mannheim), be recognized provisionally. 1. Mima polymorpha strain CDC 7833, received from P.

F i f t ys i x s t r a i n s o f " h y d r o g e n b a ct e r i a a n d r e l a t e d n o n a u t o t r o p h i c b a c t e r i a ,

S U M M A R YStrains of Pseudomonas stutzeri and related denitrifying bacteria were compared in their phenotypic properties and mean deoxyribonucleic acid (DNA) base composition. On the basis of this comparison and of in vitro DNA hybridization experiments, it was concluded that, using practical diagnostic tests, no more than two nomenspecies can be recognized within the group. One, P. stutzeri, was extremely variable in phenotypic characteristics and in DNA base composition; we included in it the strains previously assigned to P. stanieri. The other was a new species, P. rnendocina Palleroni, which was more homogeneous in phenotypic characters, and in DNA base composition and homology. The comparative properties of known denitrifying pseudomonads are tabulated. I N T R O D U C T I O NPseudomonas stutzeri is a non-fluorescent, denitrifying pseudomonad, widely distributed in soil and water. It was discovered and described as Bacillus denitrijkans I1 by Burri & Stutzer in 1895, and renamed Bacterium stutzeri by Lehmann & Neumann in I 896. Thereafter, the taxonomic and nomenclatural status of this well-characterized species became confused, and was cleared up by van Niel & Allen only in 1952, when they retraced the history of the species, and redescribed it. P. stutzeri can be distinguished from other Pseudomonas spp. by many properties, of which the salient ones are: vigorous denitrifying ability; use of starch and maltose as carbon sources; and a characteristic and unusual colony structure ; colonies of freshly isolated strains are wrinkled, tough and coherent, and have a light-brown colour which reflects the unusually high cytochrome c content of the cells.

No abstract

SUMMARYOn the basis of phenotypic characterization and DNA-DNA homology studies of strains of phytopathogenic Pseudomonas species, it is concluded that P. cepacia is so similar to P. multivorans that the latter name should be regarded as a synonym. On similar grounds, P. alliicola appears to be a synonym of P. marginata. P. caryophylli is a readily distinguishable species. From the DNA-DNA hybridization studies all of these species seem to be related to each other and to the animal pathogens P. pseudomallei and P. mallei.