Abstract
DNA base composition and degree of homology relative to Streptomyces griseus DNA of various morphologically distinct actinomycetes were studied in order to find out any genotypic difference that may exist between their DNA's, for a more rational approach to the taxonomy and phylogeny of the actinomycetes. The present results indicated that the average percentage of GC, analyzed by the paper chromatographic method, was in the range of 67.5-74.5 and, if Nocardia and its relatives be excepted, generally between 70 and 74; the difference was gradual and failed to delineate any organisms. However, organisms having the nocardial type of cell wall, i.e., Nocardia and Micropolyspora, occupied the lower region, followed by Streptosporangium and Microellobosporia. Furthermore, the DNA homology test by the DNA-agar method showed that, under the experimental conditions used, no conspicuous difference applicable to the classification was recognizable inter- and intragenerically, including even strains of Mycobacterium and Thermoactinomyces, as compared with the marked difference of E. coli used as a control. Using these data, as well as the previously reported cell-wall composition (1), a possible phylogenetic position of various mesophilic actinomycetes is presented.
