ABSTRACT
Introduction ....................................................................................................................................309 The Systematics of Bacillus Sensu Lato ........................................................................................ 310
Bacillus Systematics: The Classical Paradigm ................................................................... 310 Bacillus Systematics: The Molecular Paradigm ................................................................. 311 An Overview of Bacillus Sensu Lato ................................................................................. 311 Characterization and Classication of Novel Bacillus Isolates .......................................... 314
Industrial Applications of Bacillus ................................................................................................ 317 Developing Bacillus Strains for Industry ........................................................................... 317 Enzymes.............................................................................................................................. 319 Vitamins and Fine Chemicals ............................................................................................ 319 Agriculture .......................................................................................................................... 319
Medical Applications of Bacillus .................................................................................................. 320 Cell Physiology and Development ................................................................................................. 322 Future Technology and Applications ............................................................................................. 325 Acknowledgments .......................................................................................................................... 326 References ...................................................................................................................................... 326
The genus Bacillus represents a very large, diverse set of bacteria that have one common yet distinct feature: the ability to make dormant endospores aerobically when challenged with unfavorable growth conditions. A photograph of sporulating cells of Bacillus subtilis is shown in Figure 24.1A. In 1989, Ruth Gordon authored a chapter for the Practical Handbook of Microbiology (CRC Press) that reviewed the systematics of the genus Bacillus using the most extensive, up-to-date information at that time (Gordon, 1989). Then, the various species of Bacillus were divided into three groups based on the phenotype of the sporangia (e.g., swollen vs. non-swollen) and the mature spore (e.g., spherical, cylindrical, or ellipsoidal), and on biochemical tests (e.g., catalase, starch hydrolysis) and growth properties (e.g., 7% NaCl). The species within these groups were highly heterogeneous. Since that time, however, there have been several major reclassications of species within Bacillus caused in large part by the introduction of more sophisticated testing methods that rely on comparison at the genome level and a constant inux of new species isolated from extreme environments. Bacillus now represents just a small part of a larger taxonomic consortium of endospore-producing bacteria referred to as Bacillus sensu lato. Consequently, it is not possible in a review such as this one to provide an in-depth description of each Bacillus species. On the contrary, the goal of this work is to provide the reader with a higher level (over-arching) summary on Bacillus sensu lato, describing in large brush-strokes the common characteristics of its current members. However, the review will also attempt to focus on those key species, specically B. subtilis, that play an increasingly important role in industry, medicine, and basic science. This two-tier approach should provide the investigator with a greater appreciation of this highly interesting and adaptable group of bacteria.
