Sphingomonas pituitosa sp nov., an exopolysaccharide-producing bacterium that secretes an unusual type of sphingan

Strain EDIVT, an exopolysaccharide-producing bacterium, was subjected to po lyphasic characterization. The bacterium produced copious amounts of an ext racellular polysaccharide, forming slimy, viscous, intensely yellow-pigment ed colonies on Czapek-Dox (CZD) agar. The culture fluids of the liquid vers ion of CZD medium were highly viscous after cultivation for 5 d. Cells of s train EDIVT were Gram-negative, catalase-positive, oxidase-negative, nonspo re-forming, rod-shaped and motile. Comparisons of 16S rDNA gene sequences d emonstrated that EDIVT clusters phylogenetically with the species of the ge nus Sphingomonas sensu stricto. The G+C content of the DNA (64.5 mol%), the presence of ubiquinone Q-10, the presence of 2-hydroxymyristic acid (14:0 2-OH) as the major hydroxylated fatty acid, the absence of 3-hydroxy fatty acids and the detection of sym-homospermidine as the major component in the polyamine pattern, together with the presence of sphingoglycolipid, suppor ted this delineation. 16S rDNA sequence analysis indicated that strain EDIV T is most closely related (99.4% similarity) to Sphingomonas trueperi LMG 2 142(T). DNA-DNA hybridization showed that the level of relatedness to 5. tr ueperi is only 45.5%. Further differences were apparent in the cellular fat ty acid profile, the polar lipid pattern, the Fourier-transform infrared sp ectrum and whole-cell proteins and in a number of biochemical characteristi cs. On the basis of the estimated phylogenetic position derived from 16S rD NA sequence data, DNA-DNA reassociation and phenotypic differences, strain EDIVT (= CIP 106154(T) = DSM 13101(T)) was recognized as a new species of S phingomonas, for which the name Sphingomonas pituitosa sp. nov. is proposed . A component analysis of the exopolysaccharide (named PS-EDIV) suggested t hat it represents a novel type of sphingan composed of glucose, rhamnose an d an unidentified sugar. Glucuronic acid, which is commonly found in sphing ans, was absent. The mean molecular mass of PS-EDIV was approximately 3 x 1 0(6) Da.