oxygen affecting the growth of microorganism?

The presence of oxygen in the atmosphere is required for the survival of human beings. Contrary to this, you would realize that there are many microorganisms including bacteria, which have the ability to thrive in the absence of oxygen or free air. Microorganisms have been classified as aerobic when they require fiee oxygen, anaerobic when they grow best in the absence of free oxygen, and facultative when they grow well either aerobically or anaerobically.

Moulds are aerobic, most yeast grows best aerobically, and bacteria of different kinds may be aerobic, anaerobic or facultative. The bacteria which have the ability to thrive in the absence of oxygen or fiee air are known as 'strict' or 'obligate anaerobes'. These organisms die when exposed to air or oxygen. But there are only few obligate anaerobes. Many bacteria are referred thus, because they tolerate extremely low levels of oxygen. There is another category of bacteria, which can survive either in the presence or absence of oxygen. They are known as 'facultative anaerobesJ. The other kinds of bacteria which cannot survive in the absence of oxygen are called 'obligate aerobes'. There is yet another category of bacteria known as 'micro- aerophiles', which requires 'oxygen for survival albeit at low concentrations than present in air.