Genotype versus phenotype in the circumscription of bacterial species: the case of Pseudomonas stutzeri and Pseudomonas chloritidismutans.

The phenotypic characteristic of strain AW-1(T) of Pseudomonas chloritidismutans that is most relevant from the taxonomic point of view appears to be the capacity of growth under anaerobic conditions using chlorate as electron acceptor. This property is not restricted to this species only within the genus Pseudomonas, since it is also present in strains of genomovars 1 or 5, and 3 of Pseudomonas stutzeri. P. chloritidismutans has been described as a non-denitrifying species, but the isolation of variants that are able to grow anaerobically in the presence of nitrate is possible after subcultivation under selective conditions. The subdivision of P. stutzeri into a number of species on the basis of these characteristics does not help to clarify the phylogenetic relationships among the members of an otherwise coherent group of strains, and the considerations presented in this communication support the reclassification of the new species name P. chloritidismutans, which in our opinion, should be considered as a Junior name of P. stutzeri. A multilocus sequence analysis, together with a phenotypic analysis of the anaerobic oxidative metabolism, gives new insights into the phylogeny and evolution of the species.

A detailed phenotypic and genotypic description of Pseudomonas strain OX1.

Strain OX1 exhibits important physiological, ecological, and biotechnological properties in the degradation of chemical pollutants. It was previously classified as a member of Pseudomonas stutzeri based on its phenotypic characteristics. The present taxonomic study describes phenotypic and genomic properties of strain OX1 and illustrates the value both of multigenic sequence analysis and siderotyping methods to justify its species circumscription within the genus Pseudomonas. We have concluded that strain OX1 is a member of the Pseudomonas corrugata group, distantly related to P. stutzeri, and should be considered representative of a new species. However, phenotypic differentiation between species in this group remains difficult, and species proposals based on only a single strain must be cautious. We, therefore, prefer not to propose a new species until more strains with the same genomic and phenotypic properties as strain OX1 have been isolated.

Comparative genetic diversity of Pseudomonas stutzeri genomovars, clonal structure, and phylogeny of the species.

A combined phylogenetic and multilocus DNA sequence analysis of 26 Pseudomonas stutzeri strains distributed within the 9 genomovars of the species has been performed. Type strains of the two most closely related species (P. balearica, former genomovar 6, and P. mendocina), together with P. aeruginosa, as the type species of the genus, have been included in the study. The extremely high genetic diversity and the clonal structure of the species were confirmed by the sequence analysis. Clustering of strains in the consensus phylogeny inferred from the analysis of seven nucleotide sequences (16S ribosomal DNA, internally transcribed spacer region 1, gyrB, rpoD, nosZ, catA, and nahH) confirmed the monophyletic origin of the genomovars within the Pseudomonas branch and is in good agreement with earlier DNA-DNA similarity analysis, indicating that the selected genes are representative of the whole genome in members of the species.