During the course of studies on halophilic, Gram-negative bacteria, a comparison of two strains of halophilic bacteria, Pseudomonas halophila DSM 3050 and Halomonas variabilis DSM 3051 (formerly Halovibrio variabilis) demonstrated that the characteristics of strain DSM 3050 corresponded to the original description of Halovibrio variabilis and those of DSM 3051 to P. halophila, both of which had been isolated from the Great Salt Lake in Utah [Fendrich, C. (1988). Syst Appl Microbiol 11, 36-43]. It was concluded that these two strains did not correspond with their original descriptions, e.g. the original description of Halovibrio variabilis matched that of Pseudomonas halophila DSM 3050 and the original description of Pseudomonas halophila matched that of Halovibrio variabilis DSM 3051, which was subsequently transferred to the genus Halomonas as Halomonas variabilis DSM 3051. These findings raise the question of whether the genus name Halovibrio, with the type species Halovibrio variabilis, should be associated with type strain DSM 3050 and recognition of strain DSM 3051 as the type strain of Pseudomonas halophila.

During the course of studies on halophilic, Gram-negative bacteria, a comparison of two strains of halophilic bacteria, Pseudomonas halophila DSM 3050 and Halomonas variabilis DSM 3051 (formerly Halovibrio variabilis) demonstrated that the characteristics of strain DSM 3050 corresponded to the original description of Halovibrio variabilis and those of DSM 3051 to P. halophila, both of which had been isolated from the Great Salt Lake in Utah [Fendrich, C. (1988). Syst Appl Microbiol 11, 36-43]. It was concluded that these two strains did not correspond with their original descriptions, e.g. the original description of Halovibrio variabilis matched that of Pseudomonas halophila DSM 3050 and the original description of Pseudomonas halophila matched that of Halovibrio variabilis DSM 3051, which was subsequently transferred to the genus Halomonas as Halomonas variabilis DSM 3051. These findings raise the question of whether the genus name Halovibrio, with the type species Halovibrio variabilis, should be associated with type strain DSM 3050 and recognition of strain DSM 3051 as the type strain of Pseudomonas halophila.

The broad and vague phenotypic definition allowed the genus Pseudomonas to become a dumping ground for incompletely characterized polarly flagellated, gram-negative, rod-shaped, aerobic bacteria, and a large number of species have been accommodated in the genus Pseudomonas. The 16S rRNA sequences of 128 valid and invalid Pseudomonas species, which included almost valid species of the genus Pseudomonas listed in the Approved Lists of Bacterial Names, were obtained: sequences of 59 species were determined and those of 69 species were obtained from the GenBank/EMBL/DDBJ databases. These sequences were compared with the sequences of other species of the Proteobacteria. Fifty-seven valid or invalid species including Pseudomonas aeruginosa (type species of the genus Pseudomonas Migula 1894) belonged to the genus Pseudomonas (sensu stricto). Seven subclusters were formed in the cluster of the genus Pseudomonas (sensu stricto), and the resulting clusters conformed well to the rRNA-DNA hybridization study by Palleroni (1984). The other species did not belong to the genus Pseudomonas (sensu stricto) and were related to other genera, which were placed in four subclasses of the Proteobacteria (alpha, beta, gamma and gamma-beta subclasses). Twenty-six examined species, which were not included in the cluster of the Pseudomonas (sensu stricto) and have not been transferred to other genera as yet, are listed alphabetically: 'Pseudomonas abikonensis', Pseudomonas antimicrobica, Pseudomonas beijerinckii, Pseudomonas beteli, Pseudomonas boreopolis, 'Pseudomonas butanovora', Pseudomonas carboxydohydrogena, Pseudomonas cissicola, Pseudomonas doudoroffii, Pseudomonas echinoides, Pseudomonas elongata, Pseudomonas flectens, Pseudomonas geniculata, Pseudomonas halophila, Pseudomonas hibiscicola, Pseudomonas huttiensis, Pseudomonas iners, Pseudomonas lanceolata, Pseudomonas lemoignei, Pseudomonas mephitica, Pseudomonas pictorum, Pseudomonas saccharophila, Pseudomonas spinosa, Pseudomonas stanier, Pseudomonas syzygii and Pseudomonas woodsii. The phylogenetic affiliations of these 26 pseudomonads species are shown.