ABSTRACT
This entry provides a brief review of the biochemistry
of anaerobic microorganisms and their applications in
industrial fermentation. Anaerobic reactions are biolo-
gical processes by which complex organic materials are
decomposed partially in the absence of air to yield a
variety of reduced organic compounds (e.g., ethanol,
butanol, acetic acid, methane, and sulfide), instead of
complete aerobic combustion to CO2 and H2O. These
reactions occur everywhere in nature, ranging from
aquatic environments to the gastrointestinal tract of
animals.[1-3] Anaerobic metabolism also plays an
important role in the global sulfur[4,5] and nitrogen
cycle.[6,7] In industry, anaerobic fermentations have
been applied in wastewater treatment,[8-11] food pro-
cessing including alcoholic beverages[12] and lactic
acid-fermented foods,[13] and bulk chemical and fuel
production.[14] Metabolic pathways are usually very
complex in anaerobic microorganisms. Within the
total group of anaerobic microorganisms, four general
kinds of reactions are usually observed. They include
alcohol and ketone production by solventogens, acid
production by acidogens, methane production by
methanogens, and hydrogen sulfide production by
sulfate-reducing bacteria (SRB). The anaerobic meta-
bolisms of nitrate-reducing bacteria and facultative
anaerobic bacteria that are found in many anaerobic
wastewater treatment processes are not discussed in
this entry.
