Trong môi trường yếm khí, vi sinh vật có thể chu kỳ các hợp chất carbon để sản lượng năng lượng trong một quá trình được gọi là quá trình lên men. Carbon dioxide có thể được chuyển đổi khác được gọi là khí methane (CH4). Điều này xảy ra trong môi trường yếm khí | cules is cycled further by microorganisms in a series of reactions that form the so-called tricarboxylic acid or TCA cycle. The breakdown of the carbohydrate serves to supply energy to the microorganism. This process is also known as respiration. In anaerobic environments microorganisms can cycle the carbon compounds to yield energy in a process known as fermentation. Carbon dioxide can be converted to another gas called methane CH4 . This occurs in anaerobic environments such as deep compacted mud and is accomplished by bacteria known as methanogenic bacteria. The conversion which requires hydrogen yields water and energy for the methanogens. To complete the recycling pattern another group of methane bacteria called methane-oxidizing bacteria or methanotrophs literally methane eaters can convert methane to carbon dioxide. This conversion which is an aerobic oxygen-requiring process also yields water and energy. Methanotrophs tend to live at the boundary between aerobic and anaerobic zones. There they have access to the methane produced by the anaerobic methanogenic bacteria but also access to the oxygen needed for their conversion of the methane. Other microorganisms are able to participate in the cycling of carbon. For example the green and purple sulfur bacteria are able to use the energy they gain from the degradation of a compound called hydrogen sulfide to degrade carbon compounds. Other bacteria such as Thiobacillus ferrooxidans uses the energy gained from the removal of an electron from iron-containing compounds to convert carbon. The anerobic degradation of carbon is done only by microorganisms. This degradation is a collaborative effort involving numerous bacteria. Examples of the bacteria include Bacteroides succinogenes Clostridium butyricum and Syntrophomonas sp. This bacterial collaboration which is termed interspecies hydrogen transfer is responsible for the bulk of the carbon dioxide and methane that is released to the atmosphere. See also Bacterial
