A polycyclic aromatic hydrocarbon (PAH)-utilizing Mycobacterium strain, PYR-1(T), was isolated from petroleum-contaminated estuarine sediments and has been shown by 16S rRNA gene sequencing to be closely related to Mycobacterium aurum ATCC 23366(T) and Mycobacterium vaccae ATCC 15438(T). In this investigation, the 16S rDNA, fatty acid methyl esters, DNA-DNA hybridization, PFGE analysis of restriction-digested total genomic DNA and biochemical tests were used to determine the taxonomic relationship of strain PYR-1(T) to other closely related Mycobacterium species. The sequence of the 16S rRNA gene of strain PYR-1(T) was similar to that of Mycobacterium austroafricanum ATCC 33464(T), except for one gap at position 43. Fatty acid methyl ester analysis also showed similarity to M. austroafricanum ATCC 33464(T); however, the Euclidean distance was greater than 4.0, indicating that these strains were not identical. Dot-blot DNA-DNA hybridization of strain PYR-1(T) with M. austroafricanum indicated less than 40% relatedness. When the total chromosomal DNA of M. aurum ATCC 23366(T), M. austroafricanum ATCC 33464(T) and strain PYR-1(T) was digested with restriction enzyme Xbal and analysed by PFGE, all three organisms gave different restriction patterns. Previous studies from our laboratory have shown that the reverse-phase HPLC elution profiles of mycolic acids of strain PYR-1(T) and M. austroafricanum ATCC 33464(T) have different patterns. Based on phylogenetic analysis using 165 rRNA gene sequences, fatty acid analysis, DNA-DNA hybridization and PFGE analysis and physiological and chemotaxonomic characteristics, it is concluded that strain PYR-1(T) (= DSM 7251(T) = NRRL B-24157(T)) represents a novel species of the genus Mycobacterium, for which the name Mycobacterium vanbaalenii sp. nov. is proposed.