The Complex and Changing Genus Bacillus: A Diverse Bacterial Powerhouse for Many Applications

For years, the Bacillus genus has encompassed a heterogeneous group of individuals whose main common trait was their ability to sporulate in the presence of oxygen. This criterion has been revised, resulting in the reclassification of several species into new genera and to a redefinition of the characteristics of the members of this taxon. Currently, the species of the genus are grouped into the Subtilis clade and the Cereus clade. The former, called Bacillus sensu stricto, initially composed of B. subtilis, B. licheniformis, B. pumilus, and B. amyloliquefaciens, has subsequently incorporated new species related to these. The Cereus clade, Bacillus cereus sensu lato, consists of pathogenic species (B. anthracis, B. cereus, and B. thuringiensis) as well as others of significance in agriculture and industry. Furthermore, identifying these individuals remains complex, requiring alternatives to 16S rRNA sequencing. The ability to form spores resistant to stressful conditions provides a significant advantage over other genera, with observable differences in sporulation rates and spore structure among different species. Additionally, Bacillus spp. are known for their capacity to produce antimicrobial substances, lytic enzymes, and volatile organic compounds, each with diverse applications. Some species are even used as probiotics. This review delves into aspects related to the taxonomy and identification of microorganisms belonging to the genus Bacillus, which often present challenges. The aim is to provide a comprehensive overview of the topic. In addition, it highlights the characteristics and applications of the genus, emphasizing its importance in biotechnology and microbiology.