What is Anaerobic organism?
[[Image:Ana.png|300px|thumb|right|Thioglycolate broth is a medium used mainly to find out the oxygen requirements of microorganisms. <br/>1: Obligate aerobes need [[oxygen]]. They gather at the top of the tube where its concentration is highest. <br /> 2: [[Obligate anaerobe]]s are poisoned by oxygen, so they gather at the bottom of the tube where the oxygen concentration is lowest. <br /> 3: Facultative anaerobes can grow anywhere in tube, but they gather mostly at the top because they have more energy with oxygen. <br /> 4: Microaerophiles need [[oxygen]]: they cannot ferment or respire anaerobically. However, they are poisoned by high concentrations of oxygen. They gather in the upper part of the test tube but not the very top. <br /> 5: Aerotolerant organisms do not need oxygen as they metabolise energy anaerobically. But, unlike obligate anaerobes, they are not poisoned by [[oxygen]]. They are found evenly spread throughout the test tube]] An '''anaerobic organism''' is any [[organism|living thing]] that does not need [[oxygen]] for growth. * '''Obligate anaerobes''' will die when exposed to atmospheric levels of oxygen. * '''Facultative anaerobes''' can use oxygen when it is present. * '''Aerotolerant''' organisms can survive in the presence of oxygen, but they are anaerobic because they do not use oxygen as a [[terminal electron acceptor]]. [[Microaerophile]]s are organisms that may use oxygen, but only at low concentrations (low micromolar range); their growth is inhibited by normal oxygen concentrations (approximately 200 micromolar). [[Nanaerobe]]s are organisms that cannot grow in the presence of micromolar concentrations of oxygen, but can grow with and benefit from nanomolar concentrations of oxygen. Obligate anaerobes may use [[fermentation]] or [[anaerobic respiration]]. In the presence of oxygen, facultative anaerobes use [[aerobic respiration]]; without oxygen some of them ferment, some use anaerobic respiration. Aerotolerant organisms are strictly fermentative. Microaerophiles carry out