One of the more important uses of microorganisms is as insecticides. The bacterium Bacillus thuringiensis produces in its cytoplasm a toxic crystal that kills caterpillars such as gypsy moth larvae and tomato hornworms. The toxic crystal damages the digestive tract of the insect and allows local bacteria to invade and destroy the tissues. The bacillus is sprayed on plants during the growing season and is regarded highly for its insecticide quality.
Another bacterium that can be used as an insecticide is Bacillus popillae. This organism causes milky spore disease when it infects caterpillars.
In the mining industry, microorganisms are widely used to leach low-grade ores to extract their valuable metals. For example, copper and uranium can be leached from low-grade ores by species of Thiobacillus. This organism frees the iron ions from ferrous sulfide by oxidizing ferrous ions to ferric ions. The ferric ions then oxidize copper sulfate to a soluble form which can easily be collected.