Microbial desulfonation

Organosulfonates are widespread compounds, be they natural products of low or high molecular weight, or xenobiotics Many commonly found compounds are subject to desulfonation, even if it is not certain whether all the corresp onding enzymes are widely expressed in nature. Sulfonates require transport systems to cross the cell membrane, but few physiological data and no bioc hemical data on this topic are available, though the sequences of some of t he appropriate genes are known. Desulfonative enzymes in aerobic bacteria a re generally regulated by induction, if the sulfonate is serving as a carbo n and energy source, or by a global network for sulfur scavenging (sulfate- starvation-induced (SSI) stimulon) if the sulfonate is serving as a source of sulfur. It is unclear whether an SSI regulation is found in anaerobes. T he anaerobic bacteria examined can express the degradative enzymes constitu tively, if the sulfonate is being utilized as a carbon source, but enzyme i nduction has also been observed. At least three general mechanisms of desul fonation are recognisable or postulated in the aerobic catabolism of sulfon ates: (1) activate the carbon neighboring the C-SO3- bond and release of su lfite assisted by a thiamine pyrophosphate cofactor; (2) destabilize the C- SO3- bond by addition of an oxygen atom to the same carbon, usually directl y by oxygenation, and loss of the good leaving group, sulfite; (3) an unide ntified, formally reductive reaction. Under SSIS control, different variant s of mechanism (2) can be seen. Catabolism of sulfonates by anaerobes was d iscovered recently, and the degradation of taurine involves mechanism (1). When anaerobes assimilate sulfonate sulfur, there is one common, unknown me chanism to desulfonate the inert aromatic compounds and another to desulfon ate inert aliphatic compounds; taurine seems to be desulfonated by mechanis m (1). (C) 1999 Published by Elsevier Science B.V. All rights reserved.