noun, singular: bacterium
Microscopic, single-celled organisms belonging to Kingdom Monera that possess a prokaryotic type of cell structure, which means their cells are noncompartmentalized, and their DNA (usually circular) can be found throughout the cytoplasm rather than within a membrane-bound nucleus. They reproduce by fission or by forming spores. They can practically live everywhere. They can inhabit all kinds of environment, such as in soil, acidic hot springs, radioactive waste, seawater, deep in the Earth's crust, in stratosphere, and even in the bodies of other organisms.
Bacteria belong to Kingdom Monera, together with Cyanobacteria (blue-green algae), which are also prokaryotic. Bacteria may be classified based on their shape: spherical (cocci), rod-like (bacilli), spiral (spirochetes), or comma-shaped (vibrios). Other ways of classifying them are based on whether or not they are: gram positive or gram negative, aerobic or anaerobic, autotrophic or heterotrophic, etc.
Although some of them produce infectious diseases on humans (e.g. including cholera, syphilis, anthrax, leprosy and bubonic plague) several other bacteria have been found beneficial. For example, bacteria in the gut aid in digestion. They’re also vital in recycling nutrients, such as the fixation of nitrogen from the atmosphere. Bacteria, often Lactobacillus in combination with yeasts and molds, have been used for thousands of years in the preparation of fermented foods such as cheese, pickles, soy sauce, sauerkraut, vinegar, wine and yoghurt.
Related forms: bacterial (adjective).