Bacillus

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Bacillus anthracis

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Bacillus cereus

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Bacillus coagulans

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Bacillus natto

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Bacillus subtilis

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Bacillus thuringiensis

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etc.

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Bacillus is a genus of rod-shaped bacteria. The word bacillus is also used to describe any rod-shaped bacterium, and in this sense bacilli are found in many different groups of bacteria. When the particular genus Bacillus is referred to, it is capitalized and italicized. Likewise, Bacilli refers to the particular class Bacillus belongs to, while bacilli are any rod-shaped bacteria.

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The genus Bacillus belongs to the Firmicutes, and like most other members has a Gram-positive stain. They are either obligate or facultative aerobes, and test positive for catalase. When conditions are stressful, the cells produce oval endospores that can stay dormant for extended periods. These characters originally defined the genus, but not all such species are closely related, and many have been moved to other genera.

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Bacillus are ubiquitous in nature, including both free-living and pathogenic species. Two species are considered medically significant: B. anthracis, which causes anthrax, and B. cereus, which causes a foodborne illness similar to that of Staphylococcus. The type species is B. subtilis, and is an important model organism. It is also a notable food spoiler, as is B. coagulans.

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An easy way to isolate Bacillus is by placing non-sterile soil in a test tube with water, shaking, placing in melted mannitol salts agar, and incubating at room temperature for at least a day. Colonies are usually large, spreading and irregularly-shaped. Under the microscope, the Bacillus appear as rods, and a substantial portion usually contain an oval endospore at one end, making it bulge.

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Bacilli: Bacillales...

Firmicutes: Bacilli...

Gram-positive: Gram-positive bacteria are those that are stained dark blue or violet by gram staining, in contrast to Gram-negative bacteria, which are not affected by the stain. The stain is caused by a high amount of peptidoglycan in the cell wall, which typically, but not always lacks the secondary membrane and...