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.

Abstract

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 301T and 469T 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 301T were C18 : 1ω7c (53.3 %) and C16 : 1ω7c (22.9 %), with C14 : 0 2-OH (10.8 %) as the major 2-hydroxy fatty acid. Fatty acids of strain 469T were dominated by C18 : 1ω7c (34.4 %), C16 : 1ω7c (32.0 %) and C14 : 0 2-OH (15.2 %) as the major 2-hydroxy fatty acid. The genomic DNA G+C contents of strains 301T and 469T 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 301T were Sphingobium amiense DSM 16289T, Sphingobium vermicomposti DSM 21299T, Sphingobium yanoikuyae DSM 7462T and Sphingobium scionense DSM 19371T (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 301T and the type strains of these four Sphingobium species. Closest relatives of strain 469T were Sphingomonas suberifaciens DSM 7465T and Sphingobium scionense DSM 19371T (97.1 and 96.5 % 16S rRNA gene sequence similarity, respectively). The degree of DNA–DNA hybridization between strain 469T and Sphingomonas suberifaciens DSM 7465T was 17.9 %. Based on the results of the molecular analyses and their phenotypic characteristics, strains 301T and 469T represent two novel species of the genus Sphingobium . The name Sphingobium limneticum sp. nov. is proposed for strain 301T( = DSM25076T = LMG 26659T). The name Sphingobium boeckii sp. nov. is proposed for strain 469T ( = DSM 25079T = LMG 26901T). The polyphasic analysis also suggests that Sphingomonas suberifaciens should be reclassified as Sphingobium suberifaciens comb. nov. with Ca1T ( = EY 2404T = ATCC 49355T = CIP 105429T = DSM 7465T = ICMP 12535T = NBRC 15211T = JCM 8521T = LMG 17323T = NCPPB 3629T) as the type strain.