Taxonomic Study of Bacillus coagulans Hammer 1915 with a Proposal for Bacillus smithii sp. nov.

Abstract

Guanine-plus-cytosine (G+C) content determinations, deoxyribonucleic acid (DNA) relatedness estimations, and phenotypic similarity analyses of 90 strains identified previously as Bacillus coagulans Hammer 1915 revealed that 52 (group 1) strains were Bacillus coagulans sensu stricto; 30 of the remaining organisms segregated into two distinct DNA relatedness groups, one consisting of 26 (group 2) strains and the other of 4 (group 4) organisms. Five (group 3) strains were Bacillus licheniformis, and three (group 5) strains were B. stearothermophilus. Because group 2 was a major cluster of strains which did not correspond in their characteristics to any previously known group, efforts were made to determine its taxonomic position. Group 2, with G+C contents ranging from 37 to 40 mol%, was compared with other species generally characterized as having G+C contents ranging from 37 to 44 mol% or capable of growing at 50°C or both (namely, Bacillus alcalophilus, Bacillus azotoformans, Bacillus badius, Bacillus firmus, Bacillus globiformis, Bacillus laterosporus, Bacillus macquariensis, Bacillus marinus, Bacillus megaterium, Bacillus pumilus, and Bacillus subtilis). Low DNA relatedness values and poor matching of phenotypic characteristics strongly indicated that group 2 organisms are strains of a new species, for which the name Bacillus smithii is proposed. The type strain of the new species is strain NRRL NRS-173.