Endospore Formation in Bacillus

INTRODUCTION Several species of gram-positive bacteria are noted for their elaborate adaptive responses to conditions of nutrient depletion. These developmental changes are sometimes transient and reversible, as in the attainment of “competence” for DNA uptake and transformation among some Streptococcus , Staphylococcus , and Bacillus species, but also include examples of true cellular differentiation, as in the case of spore formation in most Bacillus and Streptomyces species. In both Bacillus and Streptomyces , sporulation is actually the culmination of a complex sequence of physiological and morphological changes, not all of which are directly connected with the generation of a spore. Many Bacillus species, for example, produce and secrete an abundance of exoenzymes and small molecules, such as proteases and antibiotics, as they sporulate (most of these substances having no apparent role in spore formation), and Streptomyces species are well known for the diversity of antibiotics and other secondary metabolites they produce as they reach stationary phase (whether or not spores are formed). A very striking sporulation-associated event (irrelevant to the formation of a viable spore) peculiar to Bacillus thuringiensis is the production of an intracellular crystalline protein aggregate (the “crystal toxin”), which has extremely potent insecticidal properties (Bechtel and Bulla 1976). Not surprisingly, the complex changes that accompany and comprise the process of Sporulation in these organisms are dependent on the temporally regulated expression of many sets of genes at multiple chromosomal locations. This paper summarizes the work of several laboratories engaged in determining how, at the molecular level, such regulation is accomplished...