Baktérium

Baktérium, or bacterium, is a single-celled prokaryotic organism in the domain Bacteria. Bacteria are characterized by a lack of a membrane-bound nucleus and other organelles. Most are only a few micrometers in size and come in shapes such as cocci, bacilli, and spirilla. A typical bacterial cell has a cell wall made of peptidoglycan (with variations between Gram-positive and Gram-negative species) and a cytoplasmic membrane; some species lack a cell wall (e.g., Mycoplasma).

The genetic material of bacteria is a single circular chromosome located in the cytoplasm; many also carry small DNA molecules called plasmids. Bacteria reproduce primarily by binary fission and can exchange genes through transformation, transduction, and conjugation, contributing to rapid adaptation.

Metabolism among bacteria is diverse. They may be autotrophic or heterotrophic, and some are photosynthetic (notably cyanobacteria), chemolithotrophic, or fermentative. They inhabit nearly every environment, from soils and oceans to extreme habitats and inside other organisms.

Ecologically, bacteria drive nutrient cycling, decomposition, and symbiotic relationships, such as nitrogen fixation in plant roots. They have wide-ranging applications in industry and biotechnology, including fermentation, production of enzymes and vitamins, and recombinant DNA technology.

Bacteria include many harmless or beneficial species, but some are pathogenic, causing diseases in humans, animals, and plants. The use of antibiotics has reduced many infections, yet antibiotic resistance is a growing global concern, highlighting the importance of surveillance and responsible use.