Taxonomic Study of Bacillus by Deoxyribonucleic Acid-Deoxyribonucleic Acid Hybridization and Interspecific Transformation

Abstract

Taxonomic relationships between various species of Bacillus were studied, using 52 test strains of 8 species, by deoxyribonucleic acid (DNA)-DNA hybridization and by testing transformability of the auxotrophic and antibiotic resistance genetic markers. Results for species identification by the conventional taxonomic method described in Bergey's Manual (8th ed., 1974) showed good agreement with the DNA-DNA hybridization data for B. licheniformis (16 strains), B. pumilus (one strain), B. coagulans (three strains), B. megaterium (three strains), B. cereus (one strain), and B. brevis (one strain). However, data for 16 of 27 test strains of B. subtilis and related species indicated lower homology indexes (20 to 25%) to the Marburg strain. Transformation of the auxotrophic markers to the wild type in the Marburg strain by DNA prepared from those strains showing lower homology to the Marburg strain was not detected, whereas the antibiotic resistance markers were transformed with the same DNA preparation. Transformation of the antibiotic resistance markers to the Marburg strain by DNA prepared from some strains of species other than B. subtilis, e.g., B. licheniformis and B. pumilus, was also detected, whereas transformation of the auxotrophic markers was not. These results strongly suggest that these two groups of B. subtilis should be divided into two different species. However, evidence suggesting the existence of a core region of DNA among a wide variety of species of Bacillus was presented.