Microoganisms are not autotroph but heterotroph organisms, that means they require organic compounds for growth and reproduction. In general, they need carbohydrates and proteins besides some vitamins and minerals. Furthermore, they need a certain water activity, an optimal temperature and a neutral pH value.
Growth and reproduction means cell division, a bacterium may divide once every twenty minutes under optimal conditions, that means eight cells out of one in one hour and two billion cells in 24 hours. A microorganism is active because of its enzymes. These enzymes are proteins and may be destroyed by heating.
Pasteurization at 65-80°C destroys 95 percent of all living microorganisms and the sterilization at 120°C for at least 15 minutes kills even spores of bacteria. Other such methods use chemicals: Inhibiting growth is called preservation and destroying organisms is called disinfection.
