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( Article Type: Explanation )

Bacteria are single-cell organisms. They are prokaryotic (which means their genetic material is not enclosed by a nuclear membrane and they do not have mitochondria or plastids). Many are decomposers, which get the nutrients they need to survive by breaking down complex organic compounds in the tissues of living or dead organisms into simpler inorganic nutrient compounds. This is why wounds must be cleaned – to prevent these organisms from living off the damaged cells of the wound and turning it ‘septic’ or infected. If wounds are left unattended long enough, gangrene (which is an advanced form of infection) may set in and can result in limb amputation or even death of the patient.

Bacteria can also seriously affect humans and domestic animals. The disease, tetanus, is caused by the bacterium, Clostridium tetani, and is characterised by muscles becoming rigid and inflexible. Anthrax, which affects cattle and sheep, is a bacterial disease. It spreads through spores and can result in Septicaemia (blood poisoning) and death in animals and humans.

Some bacteria, such as cyano bacteria (previously known as blue-green algae), can photosynthesise: they combine inorganic chemicals, using sunlight, to make the organic nutrient compounds they need to live. Whilst in the direct human context bacteria are often seen as a problem, they form a key part of the functioning of natural ecosystems. For example, of direct human value are bacteria that have been isolated, which live on oil and hydrocarbons. These have a use in dealing with oil spill clean ups and situations where oil clean-up detergents cannot be used for fear of causing other environmental damage. Bacteria occur everywhere in the biosphere and are responsible for activities ranging from the souring of milk to the decay of dead animals.