Summary auto-generated
This paper reports on a taxonomic reclassification of bacterial species within rRNA superfamily III. The researchers investigated phylogenetic relationships among Rhodocyclus gelatinosus, Leptothrix species, Sphaerotilus natans, Pseudomonas saccharophila, and Alcaligenes latus using DNA-rRNA hybridization, DNA base composition analysis, and protein gel electrophoresis. The studied organisms share high GC content (67.8-72.5 mol%) and form a distinct group within superfamily III (the beta subclass of Proteobacteria). Two major rRNA branches were identified: one containing Rhodocyclus gelatinosus strains, and another containing Leptothrix discophora and Leptothrix cholodnii. Sphaerotilus natans, P. saccharophila, and A. latus clustered with these at equivalent phylogenetic distances. Critically, Rhodocyclus gelatinosus was found to be only distantly related to the type species of genus Rhodocyclus (R. purpureus) and to R. tenuis. Based on these significant differences and clear distinctiveness from nearest phylogenetic neighbors, the authors propose transferring Rhodocyclus gelatinosus to a new genus, Rubrivivax gelatinosus gen. nov., comb. nov.
Key findings
- Rhodocyclus gelatinosus forms a separate rRNA branch from all other Rhodocyclus species and is only distantly related to R. purpureus and R. tenuis, justifying its removal from the genus Rhodocyclus
- Rubrivivax gelatinosus, Leptothrix discophora, Leptothrix cholodnii, Sphaerotilus natans, Pseudomonas saccharophila, and Alcaligenes latus represent phylogenetically distinct taxa sharing high GC content within rRNA superfamily III but with unique protein electrophoretic patterns
- DNA-rRNA hybridization analysis reveals two separate rRNA branches linked at Tm(e) 74.8±0.7°C, with Sphaerotilus natans and the facultatively autotrophic species located at this bifurcation point
- Each studied organism produced unique protein banding patterns by SDS-PAGE, indicating phenotypic diversity despite phylogenetic relationships
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Abstract
The taxonomic relationships among Rhodocyclus, Leptothrix, and Sphaerotilus species, Pseudomonas saccharophila, and Alcaligenes latus were investigated by performing DNA-rRNA hybridization experiments, by determining DNA base compositions, and by performing protein gel electrophoresis experiments. These taxa have relatively high guanine-plus-cytosine contents (67.8 to 72.5 mol%) and form a separate group within rRNA superfamily III. Rhodocyclus gelatinosus and “Leptothrix discophora” form two separate rRNA branches, which are linked at a Tm(e) level of 74.8 ± 0.7°C [Tm(e), temperature at which 50% of an DNA-rRNA hybrid is denatured]. Also situated at this Tm(e) level and therefore equidistantly related to Rhodocyclus gelatinosus and “Leptothrix discophora” are Sphaerotilus natans, P. saccharophila, and A. latus. Leptothrix cholodnii is located on the “L. discophora” rRNA branch but produces a protein pattern which is different from that of “L. discophora.” All of the other taxa which we investigated also have unique protein patterns. Since Rhodocyclus gelatinosus is only very distantly related to the type species of the genus Rhodocyclus (Rhodocyclus purpureus) and to Rhodocyclus tenuis and because it is clearly different from its nearest phylogenetic neighbors, we propose to rename this species as Rubrivivax gelatinosus gen. nov., comb. nov. The type strain remains strain NCIB 8290 (= LMG 4311).