Rhodococcus cerastii sp. nov. and Rhodococcus trifolii sp. nov., two novel species isolated from leaf surfaces

Abstract

Two Gram-positive, non-endospore-forming rods, strains C5T and T8T , were isolated from the phyllospheres of Cerastium holosteoides and Trifolium repens, respectively, and were studied in detail for their taxonomic position. 16S rRNA gene sequence analysis allocated both isolates clearly to the genus Rhodococcus . Isolate C5T was most closely related to Rhodococcus fascians and Rhodococcus yunnanensis , showing 99.2 % gene sequence similarity to both species. Strain T8T revealed the highest 16S rRNA gene sequence similarity to Rhodococcus corynebacterioides (98.8 %) and Rhodococcus kroppenstedtii (98.6 %). The quinone system of both strains was composed of dihydrogenated menaquinones with eight (major amount) as well as nine, seven and six isoprenoid units (MK-8H2, MK-9H2 MK-7H2 MK-6H2).The polar lipid profiles of strains C5T and T8T consisted of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylinositol, phosphatidylinositol mannoside and one unknown phospholipid. Additionally, strain C5T contained one unknown glycolipid, and strain T8T three unknown aminolipids. The fatty acid profiles contained major amounts of C16 : 0, C18 : 1ω9c and 10-methyl C18 : 0, which supported the grouping of the two isolates in the genus Rhodococcus . Physiological/biochemical characterization and DNA–DNA hybridizations with the type strains of the most closely related species allowed a clear phenotypic and genotypic differentiation of both strains. For this reason, we propose strain C5T ( = LMG 26203T  = CCM 7906T) as the type strain of a novel species with the name Rhodococcus cerastii sp. nov., and strain T8T ( = LMG 26204T  = CCM 7905T) as the type strain of a second novel species with the name Rhodococcus trifolii sp. nov.