Aerobic and anaerobic bacteria can be identified by growing them in liquid culture: 1: Obligate aerobic (oxygen-needing) bacteria gather at the top of the test tube in order to absorb maximal amount of oxygen. 2: Obligate anaerobic bacteria gather at the bottom to avoid oxygen. 3: Facultative bacteria gather mostly at the top, since aerobic respiration is the most beneficial one; but, as lack of oxygen does not hurt them, they can be found all along the test tube. 4: Microaerophiles gather at the upper part of the test tube but not at the top. They require oxygen but at a low concentration. 5: Aerotolerant bacteria are not affected at all by oxygen, and they are evenly spread along the test tube.
كائن لا هوائي Anaerobic ، هو قدرة الكائنات الحية على المعيشة في البيئات ، التي ينعدم فيها الأكسجين الحر ، أي غير المتحد مع عناصر أخرى .[1]