Bacillus pseudomycoides sp. nov.

Abstract

Previous DNA relatedness studies showed that strains identified as Bacillus mycoides segregated into two genetically distinct yet phenotypically similar groups, one being B. mycoides sensu stricto and the other, an unclassified taxon. In the present study, the taxonomic position of this second group was assessed by measuring DNA relatedness and determining phenotypic characteristics of an increased number of B. mycoides strains. Also determined was the second group's 16S RNA gene sequence. The 36 B. mycoides strains studied segregated into two genetically distinct groups showing DNA relatedness of about 30%; 18 strains represented the species proper and 18 the second group with intragroup DNA relatedness for both groups ranging from 70 to 100%. DNA relatedness to the type strains of presently recognized species with G+C contents of approximately 35 mol% (Bacillus alcalophilus, Bacillus cereus, Bacillus circulans, Bacillus lentus, Bacillus megaterium and Bacillus sphaericus) ranged from 22 to 37%. Although shown to be genetically distinct taxa, the two B. mycoides groups exhibited highly similar (98%) 16S RNA sequences. Phylogenetic analyses showed that both B. mycoides and the second group clustered closely with B. cereus. Although not distinguishable by physiological and morphological characteristics, the two B. mycoides groups and B. cereus were clearly separable based on fatty acid composition. The data established that the second B. mycoides group merits recognition as a new species for which the name Bacillus pseudomycoides is proposed. The type stain is NRRL B-617(T).