bakteerien

Bakteerien, or bacteria, are among the most abundant and diverse groups of organisms on Earth. They are prokaryotes, lacking a membrane-bound nucleus, and most are unicellular. Individual cells range from about 0.2 to 5 micrometers in length. They inhabit nearly every environment, from soil and water to the bodies of plants and animals.

Structure and reproduction. Most bacteria have a cell wall composed of peptidoglycan, a plasma membrane, and a cytoplasm with circular DNA located in a region called the nucleoid. Some also carry extra genetic material in plasmids. Bacteria reproduce primarily by binary fission, a rapid asexual process. Genetic variation arises through mutations and horizontal gene transfer via transformation, transduction, and conjugation.

Metabolism and ecology. Bacteria display a wide range of metabolisms: they can be aerobic, anaerobic, or facultatively anaerobic; some are photosynthetic, others rely on organic or inorganic compounds. They play essential roles in ecosystems, including nutrient cycling (carbon, nitrogen, sulfur), decomposition, and symbiotic relationships with hosts. In industry and food production, bacteria are used in fermentation and biotechnology.

Impact on health and history. Some bacteria are pathogens that cause diseases in humans, animals, and plants. Others are beneficial, contributing to digestion in the gut and protecting against pathogens. The study of bacteria dates back to Anton van Leeuwenhoek, who first observed them, and to the development of germ theory by Pasteur and Koch. The discovery of antibiotics revolutionized medicine, while modern genomics continues to reveal bacterial diversity and functions.