Bakterium

Bacterium (plural bacteria) is a unicellular microorganism in the domain Bacteria. Bacteria are prokaryotes, meaning they lack a nucleus and most other membrane-bound organelles. They exhibit diverse shapes, commonly appearing as spheres (cocci), rods (bacilli), or spirals (spirilla). Most have a cell wall containing peptidoglycan, and Gram staining distinguishes two major groups: Gram-positive and Gram-negative.

Genetic material is typically a single circular chromosome, often accompanied by small DNA molecules called plasmids. Bacteria reproduce asexually by binary fission, but can exchange genes through transformation, transduction, and conjugation, contributing to genetic diversity.

Metabolic diversity is broad. Bacteria can be photoautotrophs, chemoautotrophs, or heterotrophs, and may use aerobic respiration, anaerobic respiration, or fermentation. Some species form endospores as highly resistant dormant cells that endure extreme conditions.

Ecologically, bacteria are ubiquitous and play essential roles in nutrient cycling, decomposition, and symbiotic relationships with plants and animals. They contribute to soil fertility, biogeochemical processes, and the human microbiome, where many species are beneficial or neutral, while others can be pathogenic.

Applications and concerns: bacteria are used in food production, biotechnology, and medicine, including production of enzymes, antibiotics, and as model organisms in research. Pathogenic bacteria cause diseases, and antibiotic resistance poses ongoing public health challenges.