bacteriums

Bacterium is a single-celled prokaryotic organism that makes up a large portion of the microbial world. Bacteria are found in nearly every habitat, including soil, water, air, and the bodies of living organisms. They vary greatly in shape, from spheres (cocci) to rods (bacilli) to spirals, and range in size from about 0.2 to several micrometers.

All bacteria share a core cellular organization: a cell membrane, cytoplasm, ribosomes, and a generally circular chromosome located in the cytoplasm. Most have a rigid cell wall, and in many species it contains peptidoglycan. Some lack a cell wall (such as Mycoplasma). Most reproduce asexually by binary fission, but they can exchange genetic material via transformation, transduction, and conjugation, promoting adaptation.

Metabolism among bacteria is diverse. They can be autotrophic or heterotrophic, and may obtain energy through photosynthesis, oxidation-reduction reactions, or fermentation. Some fix atmospheric nitrogen, while others decompose organic matter. Bacteria often live in communities that form biofilms and use quorum sensing to coordinate behavior.

Impact on humans and ecosystems: Beneficial roles include digestion, nutrient cycling, production of fermented foods, and biotechnology. Pathogenic species cause diseases such as tuberculosis, cholera, and urinary tract infections. The widespread use of antibiotics has led to resistance, posing a major public health challenge.

Terminology: The singular form is bacterium; the standard plural is bacteria. The form bacteriums is rarely used and is generally avoided in formal writing.