Sphingobium limneticum sp. nov. and Sphingobium boeckii sp. nov., two freshwater planktonic members of the family Sphingomonadaceae, and reclassification of Sphingomonas suberifaciens as Sphingobium suberifaciens comb. nov.

Two novel chemo-organoheterotrophic members of the Sphingomonadaceae were isolated from alpine and pre-alpine lakes. Cells stained gram-negative, were motile and rod-shaped, and formed yellow, circular, convex colonies on different agar media. Strains 301(T) and 469(T) were strictly aerobic, catalase- and oxidase-positive, and grew at temperatures between 10 and 40 °C (optimum, 28 °C), and at pH values between 5 and 10 (optimum, pH 7). Both strains contained Q-10 as the dominant quinone, sphingoglycolipids and 2-hydroxymyristic acid, whereas 3-hydroxy fatty acids were absent. Major fatty acids of strain 301(T) were C(18 : 1)ω7c (53.3 %) and C(16 : 1)ω7c (22.9 %), with C(14 : 0) 2-OH (10.8 %) as the major 2-hydroxy fatty acid. Fatty acids of strain 469(T) were dominated by C(18 : 1)ω7c (34.4 %), C(16 : 1)ω7c (32.0 %) and C(14 : 0) 2-OH (15.2 %) as the major 2-hydroxy fatty acid. The genomic DNA G+C contents of strains 301(T) and 469(T) were 63.4 and 64.6 mol%, respectively. 16S rRNA gene sequence comparison indicated that both strains belonged to the genus Sphingobium. This classification was supported by the presence of spermidine as the major polyamine. The phylogenetically closest relatives of strain 301(T) were Sphingobium amiense DSM 16289(T), Sphingobium vermicomposti DSM 21299(T), Sphingobium yanoikuyae DSM 7462(T) and Sphingobium scionense DSM 19371(T) (98.8, 98.0, 97.9 and 97.4 % sequence similarity, respectively). DNA-DNA hybridization of genomic DNA yielded similarities in the range 43.2-12.1 % between strain 301(T) and the type strains of these four Sphingobium species. Closest relatives of strain 469(T) were Sphingomonas suberifaciens DSM 7465(T) and Sphingobium scionense DSM 19371(T) (97.1 and 96.5 % 16S rRNA gene sequence similarity, respectively). The degree of DNA-DNA hybridization between strain 469(T) and Sphingomonas suberifaciens DSM 7465(T) was 17.9 %. Based on the results of the molecular analyses and their phenotypic characteristics, strains 301(T) and 469(T) represent two novel species of the genus Sphingobium. The name Sphingobium limneticum sp. nov. is proposed for strain 301(T)( = DSM25076(T) = LMG 26659(T)). The name Sphingobium boeckii sp. nov. is proposed for strain 469(T) ( = DSM 25079(T) = LMG 26901(T)). The polyphasic analysis also suggests that Sphingomonas suberifaciens should be reclassified as Sphingobium suberifaciens comb. nov. with Ca1(T) ( = EY 2404(T) = ATCC 49355(T) = CIP 105429(T) = DSM 7465(T) = ICMP 12535(T) = NBRC 15211(T) = JCM 8521(T) = LMG 17323(T) = NCPPB 3629(T)) as the type strain.