Rhodococcus tukisamuensis sp. nov., isolated from soil

Researchers isolated a novel bacterial strain, Mb8T, from soil in Sapporo, Japan, during a study screening for bacteria that degrade exopolysaccharides. Comprehensive morphological, biochemical, and molecular analyses were performed to characterize this strictly aerobic, non-motile, Gram-positive organism. The strain exhibits typical Rhodococcus characteristics, including mycolic acids with 44-52 carbon atoms, meso-diaminopimelic acid in the cell wall, and a G+C content of 66.0 mol%. Phylogenetic analysis based on 16S rDNA sequencing places strain Mb8T within the R. erythropolis subclade, most closely related to R. maanshanensis with 98.0% sequence similarity. However, DNA-DNA hybridization studies showed relatedness values below 70% to all tested Rhodococcus type strains, and the strain exhibits distinct phenotypic properties. Based on these genotypic and phenotypic differences, strain Mb8T is proposed as the type strain of a novel species, Rhodococcus tukisamuensis, named after Tukisamu in Sapporo where it was isolated.

Key findings

• Strain Mb8T represents a novel Rhodococcus species isolated from Japanese soil with 66.0 mol% G+C content and characteristic mycolic acids (44-52 carbon atoms)
• 16S rDNA analysis places the strain in the R. erythropolis subclade with 98.0% similarity to R. maanshanensis but DNA-DNA hybridization shows only 45% relatedness
• The organism is a strictly aerobic, non-motile, Gram-positive rod that forms filaments or branches in early growth and converts to cocci in stationary phase
• Phenotypic properties including carbohydrate utilization and decomposition patterns distinguish strain Mb8T from all other tested Rhodococcus species
• The strain was identified during selective enrichment using exopolysaccharides as the sole carbon source, demonstrating its ability to degrade these polymers