PHOSPHOESTERASE ACTIVITY AND PHOSPHATE RELEASE FROM TRIBUTYL-PHOSPHATE BY A CITROBACTER SP

Tributyl phosphate (TBP) and other alkyl phosphates represent a class of persistent organophosphorus compounds of widespread use. Biodegrada tion of the phosphotriesters is postulated to occur through sequential hydrolytic cleavages via the phosphodiester and monoester intermediat es to alcohol and inorganic phosphate (P-i). Immobilized cells of a Ci trobacter sp. liberated P-i upon challenge with TBP but the reaction w as short-lived. In vitro studies with purified phosphomonoesterase (ph osphatase) used P-31 nuclear magnetic resonance to demonstrate P-i tra nsfer onto ethanol (phosphotransferase activity). This suggested that in vivo the onset of a futile phosphohydrolytic and transphosphorylati on cycle would limit the extent of phosphate production. A mutant defi cient in the transphosphorylating phosphomonoesterase showed an extend ed release of P-i under challenge with TBP that was not subject to the complete and premature reaction termination that precluded applicatio n of the parent strain to possible industrial processes for alkyl phos phate biodegradation.