Production, modification, and consumption of atmospheric trace gases by microorganisms

Some trace gases are contained in the atmosphere in appreciable amounts: methane, carbon monoxide, hydrogen, nitrous oxide. The bulk of these gases is of biological origin. Hydrogen is a primary product of microbial metabolism under anaerobic conditions. However, before reaching the atmosphere, it is converted by methane bacteria to methane, by nitrate reducing bacteria to nitrogen and to nitrous oxide and by sulfate reducing bacteria to hydrogen sulfide. Carbon monoxide is produced from certain organic compounds. Hydrogen, methane, and carbon monoxide are quickly oxidized by microorganisms under aerobic conditions. However, especially methane and carbon monoxide reach the atmosphere. The literature dealing with the microorganisms and biochemical reactions involved in the production and conversion of trace gases is reviewed.