baciller

A baciller is a term used to describe a bacterium with a rod-shaped morphology. In English, the singular is often bacillus and the plural bacilli. The term emphasizes shape rather than a single taxonomic group, and many different genera include bacillary species, notably Bacillus and Clostridium, as well as others such as Listeria and some Escherichia species.

Physically, bacilli are cylindrical cells that typically range from about 0.2 to 0.8 micrometers in width and several micrometers in length. They may occur singly, in pairs, in chains (diplobacilli or streptobacilli), or in other arrangements depending on genus and growth conditions. Gram staining commonly separates bacilli into two broad groups: Gram-positive rods and Gram-negative rods, though shape alone is not definitive for taxonomy.

Reproduction occurs mainly by binary fission. Many bacilli are capable of forming endospores under adverse conditions; these spores are highly resistant to heat, desiccation, and chemicals and aid survival and dissemination. Spore formation is a characteristic feature of several Bacillus and Clostridium species but is not universal among bacilli.

Ecologically, bacilli are widespread in soil, water, air, plants, and the intestines of animals. They participate in nutrient cycling and fermentation. Some are pathogenic, such as Bacillus anthracis (anthrax) and Bacillus cereus (foodborne illness), while others are harmless or beneficial and used in industry or research. Nonpathogenic bacilli are common in laboratories and industrial settings due to their robustness and metabolic versatility.

Biotechnologically, Bacillus subtilis is a well-studied model organism and production host for enzymes, proteins, and industrial compounds. Knowledge of bacillar morphology aids microscopy, diagnostics, and taxonomy, though accurate identification typically relies on genetic and biochemical data in addition to shape.