Summary auto-generated
This taxonomic study demonstrates that Pseudomonas elongata, originally classified in the genus Pseudomonas, should be reclassified as Microbulbifer elongatus based on comprehensive molecular and chemical evidence. Phylogenetic analysis of 16S rDNA sequences revealed that P. elongata is significantly more closely related to the genus Microbulbifer than to authentic pseudomonads, sharing 97.5-98.2% sequence similarity with known Microbulbifer species but less than 92% similarity with Pseudomonas species. Chemotaxonomic analyses supported this reclassification: P. elongata contains ubiquinone-8 as its predominant respiratory lipoquinone and iso-C15:0 as its major fatty acid, both characteristic of Microbulbifer rather than Pseudomonas. DNA-DNA hybridization studies established that P. elongata represents a distinct genomic species from the two previously recognized Microbulbifer species, M. hydrolyticus and M. salipaludis. Despite minor morphological differences, including distinctive yellowish-brown colony pigmentation and elongated cell morphology, the molecular evidence overwhelmingly supported taxonomic transfer. The authors formally propose the new combination Microbulbifer elongatus comb. nov., correcting a long-standing taxonomic misclassification.
Key findings
- 16S rDNA phylogenetic analysis shows Pseudomonas elongata clusters with Microbulbifer species (97.5-98.2% sequence similarity) rather than authentic pseudomonads (<92% similarity)
- P. elongata contains ubiquinone-8 and iso-C15:0 fatty acid as major components, matching Microbulbifer characteristics, not Pseudomonas characteristics which have ubiquinone-9 and different fatty acids
- DNA-DNA hybridization reveals P. elongata is genomically distinct from M. hydrolyticus (11.4% relatedness) and M. salipaludis (8.5% relatedness), confirming species status within genus
- Phylogenetic trees from three independent algorithms consistently place P. elongata within the Microbulbifer clade with 100% bootstrap confidence
- Formal reclassification proposed as Microbulbifer elongatus comb. nov., despite morphological differences in colony color and cell shape
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Abstract
Phylogenetic analysis based on 16S rDNA sequences revealed that Pseudomonas elongata Humm 1946 is more closely related to the genus Microbulbifer than to authentic pseudomonads. The type strain of P. elongata (DSM 6810T) exhibited 16S rDNA similarity levels of 97·5 and 98·2 % to the type strains of Microbulbifer hydrolyticus and Microbulbifer salipaludis, respectively, but of less than approximately 92 % to Pseudomonas species with known 16S rDNA sequences. Respiratory lipoquinone and cellular fatty acid analyses showed that the type strain of P. elongata has characteristics similar to those of the genus Microbulbifer, not those of the genus Pseudomonas. P. elongata DSM 6810T contained ubiquinone-8 as the predominant respiratory lipoquinone and iso-C15 : 0 as the major fatty acid. DNADNA relatedness data indicate that P. elongata is a species distinct from M. hydrolyticus and M. salipaludis. Therefore, on the basis of these data, P. elongata Humm 1946 should be transferred to the genus Microbulbifer as Microbulbifer elongatus comb. nov.