Enrichment of an endosulfan-degrading mixed bacterial culture

An endosulfan-degrading mixed bacterial culture was enriched from soil with a history of endosulfan exposure. Enrichment was obtained by using the ins ecticide as the sole source of sulfur, Chemical hydrolysis was minimized by using strongly buffered culture medium (pH 6.6), and the detergent Tween 8 0 was included to emulsify the insecticide, thereby increasing the amount o f endosulfan in contact with the bacteria. No growth occurred in control cu ltures in the absence of endosulfan, Degradation of the insecticide occurre d concomitant with bacterial growth. The compound was both oxidized and hyd rolyzed, The oxidation reaction favored the alpha isomer and produced endos ulfate, a terminal pathway product. Hydrolysis involved a novel intermediat e, tentatively identified as endosulfan monoaldehyde on the basis of gas ch romatography-mass spectrometry and chemical derivatization results. The acc umulation and decline of metabolites suggest that the parent compound was h ydrolyzed to the putative monoaldehyde, thereby releasing the sulfite moiet y required for growth. The monoaldehyde was then oxidized to endosulfan hyd roxyether and further metabolized to (a) polar product(s). The cytochrome P 450 inhibitor, piperonyl butoxide, did not prevent endosulfan oxidation or the formation of other metabolites. These results suggest that this mixed c ulture is worth investigating as a source of endosulfan-hydrolyzing enzymes for use in enzymatic bioremediation of endosulfan residues.