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The aerobic endospore-forming bacteria (AEFB) comprise species of Bacillus and related genera, allocated in the phylum Firmicutes. Although Bacillus spp. are among the first bacteria to be characterised, the wide diversity renders appropriate categorisation and generalisations challenging tasks. To determine genetic diversity, analyses at the molecular level are the most accurate. However, gene expression, morphological, biochemical, and physiological aspects must also be considered. The metabolism of bacteria is adapted to their natural environment or host. Thus, metabolic outlines can be used for identifying AEFB, form the basis of the formal description of bacterial taxa, and are strongly recommended for taxonomic purposes. This work addressed the biochemical and physiological profiles of 312 environmental AEFB—designated as SDF (Solo do Distrito Federal)—by performing 30 tests. Out of it, 246 were classified by 16S rRNA gene sequences. We summarised the phenotypic test relationships among selected SDF strains using a Pearson correlation-based clustering represented in heatmaps. In practice, biochemical and physiological profiles are often less discriminatory than molecular data and may be unstable because of the loss of traits. Though these test reactions are not universally positive or negative within species, they may define biotypes and be efficient strain markers, enhancing the accuracy of unknown sample identification. It can be also helpful in selecting the best represent the phenotypes of samples. Along with the other phenotypic and genotypic data, the present results will be of great importance for the robust classification of the SDF strains within the scope of the polyphasic approach.

Many species in the order Bacillales form a specialized cell type called a spore that is resistant to a range of environmental stresses. Transmission electron microscopy (TEM) reveals that the spore is comprised of a series of concentric shells, surrounding an interior compartment harbouring the spore DNA. The outermost of these shells varies considerably in morphology among species, likely reflecting adaptations to the highly diverse niches in which spores are found. To better characterize the variation in spore ultrastructure among diverse species, we used TEM to analyse spores from a collection of 23 aerobic spore-forming bacteria from the Solo do Distrito Federal (SDF strains), spanning the genera Bacillus, Lysinibacillus, Paenibacillus and Brevibacillus, isolated from soil from central Brazil. We found that the structures of these spores varied widely, as expected. Interestingly, even though these isolates are novel strains of each species, they were structurally very similar to the known examples of each species in the literature. Because in most cases, the species we analysed are poorly characterized, our data provide important evidence regarding which structural features are likely to be constant within a taxon and which are likely to vary.