they promote plant growth by volatile emissions. some species of bacillus are naturally competent for dna uptake by transformation. two bacillus species are medically significant: b. anthracis, which causes anthrax; and b. cereus, which causes food poisoning, with symptoms similar to that caused by staphylococcus. b. cereus produces toxins which cause two different set of symptoms: emetic toxin which can cause vomiting and nausea diarrhea b. thuringiensis is an important insect pathogen, and is sometimes used to control insect pests. b. subtilis is an important model organism. it is also a notable food spoiler, causing ropiness in bread and related food. b. subtilis can also produce and secrete antibiotics. some environmental and commercial strains of b. coagulans may play a role in food spoilage of highly acidic, tomato-based products. industrial significance many bacillus species are able to secrete large quantities of enzymes. bacillus amyloliquefaciens is the source of a natural antibiotic protein barnase (a ribonuclease), alpha amylase used in starch hydrolysis, the protease subtilisin used with detergents, and the bamh1 restriction enzyme used in dna research. a portion of the bacillus thuringiensis genome was incorporated into corn (and cotton) crops. the resulting gmos are resistant to some insect pests. bacillus subtilis (natto) is the key microbial participant in the ongoing production of the soya-based traditional natto fermentation, and some bacillus species are on the food and drug administration's gras (generally regarded as safe) list. the capacity of selected bacillus strains to produce and secrete large quantities (20–25 g/l) of extracellular enzymes has placed them among the most important industrial enzyme producers. the ability of different species to ferment in the acid, neutral, and alkaline ph ranges, combined with the presence of thermophiles in the genus, has led to the development of a variety of new commercial enzyme products with the desired temperature, ph activity, and stability properties to address a variety of specific applications. classical mutation and (or) selection techniques, together with advanced cloning and protein engineering strategies, have been exploited to develop these products. efforts to produce and secrete high yields of foreign recombinant proteins in bacillus hosts initially appeared to be hampered by the degradation of the products by the host proteases. recent studies have revealed that the slow folding of heterologous proteins at the membrane-cell wall interface of gram-positive bacteria renders them vulnerable to attack by wall-associated proteases. in addition, the presence of thiol-disulphide oxidoreductases in b. subtilis may be beneficial in the secretion of disulphide-bond-containing proteins. such developments from our understanding of the complex protein translocation machinery of gram-positive bacteria should allow the resolution of current secretion challenges and make bacillus species preeminent hosts for heterologous protein production. bacillus strains have also been developed and engineered as industrial producers of nucleotides, the vitamin riboflavin, the flavor agent ribose, and the supplement poly-gamma-glutamic acid. with the recent characterization of the genome of b. subtilis 168 and of some related strains, bacillus species are poised to become the preferred hosts for the production of many new and improved products as we move through the genomic and proteomic era. use as model organism colonies of the model species bacillus subtilis on an agar plate bacillus subtilis is one of the best understood prokaryotes, in terms of molecular and cellular biology. its superb genetic amenability and relatively large size have provided the powerful tools required to investigate a bacterium from all possible aspects. recent improvements in fluorescent microscopy techniques have provided novel insight into the dynamic structure of a single cell organism. research on b. subtilis has been at the forefront of bacterial molecular biology and cytology, and the organism is a model for differentiation, gene/protein regulation, and cell cycle events in bacteria.