bakterija

Bakterija (bacterium) is a single-celled prokaryotic organism in the domain Bacteria. It lacks a membrane-bound nucleus and most organelles found in eukaryotic cells. Bacteria vary in size and shape, commonly cocci (spherical), bacilli (rod-shaped), or spirilla (spiral). Most have a cell wall containing peptidoglycan and a cell membrane beneath it. The cytoplasm contains a single circular chromosome and often plasmids.

Genetic material is not enclosed in a nucleus. Reproduction is usually by binary fission, enabling rapid population growth. Variation arises by mutation and by horizontal gene transfer through transformation, transduction, and conjugation.

Metabolism and ecology: Bacteria show diverse metabolism. They can be autotrophic, using light or chemical energy; most are heterotrophic, consuming organic compounds. They can be aerobic, anaerobic, or facultative. Some perform photosynthesis, others decompose matter; nitrogen fixation occurs in certain species.

Ecological roles and health: They play essential roles in ecosystems, including decomposition and nutrient cycling. They are part of the human microbiota, aiding digestion and immune function. A minority are pathogens capable of causing disease; antibiotics and resistance are major concerns in medicine.

Classification and study: Bacteria are classified by shape, staining properties (Gram-positive or Gram-negative), metabolism, and genetics. In the lab, they are grown on culture media; Gram staining distinguishes major groups. Research covers ecology, evolution, pathogenesis, and biotechnology.

Note: This article uses general terms; many bacteria have diverse attributes and exceptions to these general statements.