Summary auto-generated
This study used 16S rRNA gene sequencing to comprehensively reclassify the genus Pseudomonas, which had become a taxonomically problematic group. The researchers analyzed 128 Pseudomonas species (57 new sequences determined, 69 from databases) and compared them to other Proteobacteria. They found that only 57 species belong to the authentic genus Pseudomonas (sensu stricto), which was confirmed by agreement with prior rRNA-DNA hybridization studies. The remaining species were distributed across four Proteobacteria subclasses (α, β, γ, and γ-β). Many previously misclassified species were correctly assigned to other established genera including Burkholderia, Sphingomonas, Ralstonia, Burkholderia, Comamonas, and others. The study identified 26 Pseudomonas species that remain unassigned to other genera, mapping their phylogenetic affiliations. Within authentic Pseudomonas, seven subclusters were identified corresponding to known species groups. This work resolved significant taxonomic confusion by using molecular data to restore phylogenetic clarity to a historically problematic bacterial genus.
Key findings
- Only 57 of 128 examined Pseudomonas species belong to the authentic genus Pseudomonas sensu stricto, with the type species P. aeruginosa confirming the grouping
- 71 Pseudomonas species were reclassified into other genera across multiple Proteobacteria subclasses, correcting longstanding taxonomic misplacements
- Seven distinct phylogenetic subclusters were identified within authentic Pseudomonas, correlating well with previous rRNA-DNA hybridization classifications
- 26 previously misnamed Pseudomonas species have defined phylogenetic affiliations but require formal reclassification to new or existing genera
- 16S rRNA sequence analysis successfully resolved the heterogeneous genus Pseudomonas into coherent phylogenetic groups aligned with true evolutionary relationships
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Abstract
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 54>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.