MICROBIAL-METABOLISM OF SULFUR-CONTAINING AND PHOSPHORUS-CONTAINING XENOBIOTICS

The enzymes involved in the microbial metabolism of many important pho sphorus- or sulfur-containing xenobiotics, including organophosphate i nsecticides and precursors to organosulfate and organosulfonate deterg ents and dyestuffs have been characterized. In several instances their genes have been cloned and analysed. For phosphonate xenobiotics, the enzyme system responsible for the cleavage of the carbon-phosphorus b ond has not yet been observed in vitro, though much is understood on a genetic level about phosphonate degradation. Phosphonate metabolism i s regulated as part of the Pho regulon, under phosphate starvation con trol. For organophosphorothionate pesticides the situation is not so c lear, and the mode of regulation appears to depend on whether the comp ounds are utilized to provide phosphorus, carbon or sulfur for cell gr owth. The same is true for organosulfonate metabolism, where different (and differently regulated) enzymatic pathways are involved in the ut ilization of sulfonates as carbon and as sulfur sources, respectively. Observations at the protein level in a number of bacteria suggest tha t a regulatory system is present which responds to sulfate limitation and controls the synthesis of proteins involved in providing sulfur to the cell and which may reveal analogies between the regulation of pho sphorus and sulfur metabolism.