Systematics and Ecology of Bacillus

Abstract

This chapter provides a review of current ideas concerning the systematics of the aerobic endospore-forming bacteria and shows how an appreciation of their classification and identification makes possible for a better understanding of their ecology. The DNA base composition of thermoactinomycete species is around 50 to 54% G+C, which is much lower than the 60% or more found in the true actinomycetes. 16S rRNA analyses have placed Thermoactinomyces species firmly alongside other thermophilic Bacillus species, and the sequences show very low homology with actinomycete rRNA sequences. It is possible to allocate many Bacillus species to one of six taxa that have distinguishable physiologies and, perhaps surprisingly, are generally consistent with the division of the genus based on spore morphologies. Phylogenetic trees of some members of the genus Bacillus based on 16S rRNA sequence analysis are provided in the chapter. That Bacillus species constitute discrete genetic and phenetic entities raises interesting questions with regard to gene exchange and the evolution of the species. The increased number of well-defined Bacillus species described together with the physiological diversity that they will undoubtedly represent will present a formidable challenge to the taxonomist, but the outcome should be a fascinating insight into the evolutionary history of these bacteria and perhaps of endospore formation itself.