Relationships among mycobacteria and nocardiae based upon deoxyribonucleic acid reassociation

The degree of renaturation between Nocardia farcinica 330 deoxyribonucleic acid (DNA) and DNA from 17 nocardial strains and 11 mycobacterial strains, and between Mycobacterium smegmatis 405 DNA and DNA from 11 mycobacterial strains and 14 nocardial strains was determined by using the nitrocellulose membrane filter technique. These results indicated that some cultures designated N. farcinica were identical to some cultures designated N. asteroides but that other strains called N. asteroides were distinctly different. The species M. smegmatis was homogeneous and distinct from the other species examined. Data comparing the extent of nucleotide sequences shared by M. smegmatis 405 DNA and DNA from nine other mycobacterial strains, as determined by the membrane filter technique and by monitoring DNA reassociation optically, were similar. The extent of reassociation between M. tuberculosis H37Ra DNA and DNA from 14 mycobacterial strains was determined optically. DNA from M. bovis BCG was 86% homologous with M. tuberculosis H37Ra DNA. The other mycobacterial DNA preparations examined were less than 40% homologous with M. tuberculosis H37Ra DNA. The genome sizes of the mycobacteria examined ranged between 2.5 x 10(9) daltons and 4.5 x 10(9) daltons.