f Transfer of Rhodocyclus gelatinosus to Rubrivivax gelatinosus gen. nov., comb. nov., and Phylogenetic Relationships with Leptothrix, Sphaerotilus natans, Pseudomonas saccharophila, and Alcaligenes latus

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).