Representative strains of Nocardioides, Arthrobacter simplex and Arthrobacter tumescens were degraded by acid methanolysis and the fatty acid esters released examined by thin-layer and gas chromatography. Branched-chain 14-methylpentadecanoic acid (iso-16) was the predominant component in all but one of the Nocardioides strains. Arthrobacter simplex also contained major amounts of this acid whereas A. tumescens had only minor amounts. All of the test strains possessed 15 and 17 carbon straight chain acids, tuberculostearic acid (10-methyloctadecanoic acid) and its 17 and 18-carbon homologues. The fatty acid profiles of Nocardioides strains lacked 13-methyltetradecanoic and heptadecanoic acids which were both present in Arthrobacter simplex and Arthrobacter tumescens. The profiles of these latter organisms were quantitatively different from each other. The polar lipids of the test strains all contained diphosphatidylglycerol and phosphatidylglycerol but only Arthrobacter tumescens contained phosphatidylinositol and three unidentified polar lipids. Nocardioides and Arthrobacter simplex strains all contained two very characteristic closely related polar lipids. All of the test strains contained tetrahydrogenated menaquinones with eight isoprene units as the major isoprenologue. The results of the present study support the integrity of the genus Nocardioides and provide a reliable way of distinguishing it from other actinomycetes, such as Streptomyces, which also have LL-diaminopimelic acid and glycine in the peptidoglycan. The lipid data, together with results from chemical, genetic and phage host range studies, provide sufficient grounds for the transfer of Arthrobacter simplex to Nocardioides as Nocardioides simplex comb. nov. An emended description of the genus Nocarioides is given.

Our phylogenetic analysis based on 16S ribosomal DNA (rDNA) sequences and chemotaxonomic analyses showed that Nocardioides simplex ATCC 13260, ATCC 19565, and ATCC 19566 are more closely related to the genus Rhodococcus, especially Rhodococcus erythropolis, than to the genus Nocardioides. N. simplex ATCC 13260 and N. simplex ATCC 19565 and ATCC 19566 exhibited levels of 16S rDNA similarity of 99.4 and 100%, respectively, to R. erythropolis DSM 43066T. Strains ATCC 13260, ATCC 19565, and ATCC 19566 had mesodiaminopimelic acid in their peptidoglycan and MK-8(H2) as their predominant menaquinone. These three strains produced cellular fatty acid patterns similar to those of R. erythropolis strains rather than those of Nocardioides species. Therefore, N. simplex ATCC 13260, ATCC 19565, and ATCC 19566 should be reclassified as strains of R. erythropolis Gray and Thornton 1928.