Reclassification and emended description of Caulobacter leidyi as Sphingomonas leidyi comb. nov., and emendation of the genus Sphingomonas

Abstract

‘ Caulobacter leidyi ’ DSM 4733T has been shown to be affiliated with the family Sphingomonadaceae instead of the Caulobacteraceae , and due to its poor characterization has been omitted from the current edition of Bergey’s Manual of Systematic Bacteriology and removed to limbo. We isolated a novel sphingoglycolipid-containing dimorphic prosthecate bacterium, designated strain 247, from a pre-alpine freshwater lake. Strain 247 and ‘ Caulobacter leidyi ’ DSM 4733T were characterized in detail. The rod-shaped cells were Gram-stain-negative, aerobic, catalase- and oxidase-positive, and formed a stalk or polar flagellum. Both strains grew optimally at 28–30 °C, and pH 6.0–8.0. The major fatty acids were C18 : 1ω7c, C16 : 0 and 11-methyl C18 : 1ω7c. C14 : 0 2-OH represents the major 2-hydroxy fatty acid. Q-10 was the major respiratory quinone and the major polar lipids were diphosphatidylglycerol, phosphatidyldimethylethanolamine, phosphatidylglycerol, phosphatidylmonomethylethanolamine, phosphatidylethanolamine, phosphatidylcholine, three glycolipids, two phosphoaminolipids and two unidentified sphingoglycolipids. The major polyamine was sym-homospermidine. The G+C content of genomic DNA of strains 247 and DSM 4733T was 67.6 mol% and 67.0 mol%, respectively. According to 16S rRNA gene sequence analysis and DNA–DNA hybridization, strains DSM 4733T and 247 were phylogenetically closely related (99.6 % 16S rRNA gene sequence similarity, 82.9 % DNA–DNA hybridization value) and affiliated to the genus Sphingomonas . The closest recognized species was Sphingomonas aquatilis DSM 15581T (98.1 % sequence similarity). In addition, the presence of cystine arylamidase, absence of β-galactosidase, and the inability to utilize l-arabinose, galactose and sucrose distinguished strains DSM 4733T and 247 from most other members of the family Sphingomonadaceae . So far, the dimorphic life cycle that involves a prosthecate and a flagellated stage is unique for strains DSM 4733T and 247 among all members of the family Sphingomonadaceae . Therefore, Caulobacter leidyi is reclassified as Sphingomonas leidyi, with the type strain DSM 4733T ( = ATCC 15260T = CIP 106443T = VKM B-1368T) and strain 247 (DSM 25078 = LMG 26658) as an additional strain of this species.