BacillusStrains Most Closely Related toBacillus nealsoniiAre Not Effectively Circumscribed within the Taxonomic Species Definition

Abstract

Bacillusstrains with >99.7% 16S rRNA gene sequence similarity were characterized with DNA:DNA hybridization, cellular fatty acid (CFA) analysis, and testing of 100 phenotypic traits. When paired with the most closely related type strain, percent DNA:DNA similarities (%S) for sixBacillusstrains were all far below the recommended 70% threshold value for species circumscription withBacillus nealsonii. An apparent genomic group of fourBacillusstrain pairings with 94%–70%Swas contradicted by the failure of the strains to cluster in CFA- and phenotype-based dendrograms as well as by their differentiation with 9–13 species level discriminators such as nitrate reduction, temperature range, and acid production from carbohydrates. The novelBacillusstrains were monophyletic and very closely related based on 16S rRNA gene sequence. Coherent genomic groups were not however supported by similarly organized phenotypic clusters. Therefore, the strains were not effectively circumscribed within the taxonomic species definition.