| The approach of this research was to isolate a microorganism capable of acquiring sulfur from endosulfan by placing soil bacteria under increasingly stringent pressure to capture the endosulfan sulfur moiety for growth under stable neutral pH conditions. In the first phase of research, a soil microbe identified as Pseudomonas aeruginosa was isolated which utilized both the {dollar}alpha{dollar} and {dollar}beta{dollar} isomers of endosulfan but not endosulfan sulfate as a sole source of sulfur. This microbe appeared to possess a unique ability to capture sulfur from endosulfan and, as such, was given the strain designation of WSC for Wadmalaw Island, S.C. site of its discovery.; During the second phase, the products and rates of this biotransformation reaction were investigated. The biotransformation of endosulfan produced endodiol as the principal product which represented a 100-fold decrease in the toxicity of the parent compounds. The rate of endosulfan disappearance observed during the exponential growth phase of the bacterium was 0.38 and 0.26 nmol/hr/L for {dollar}alpha{dollar}- and {dollar}beta{dollar}-endosulfan, respectively, which was 24 times faster than previously reported rates for abiotic hydrolysis under comparable pH conditions. A yield coefficient of 24 mg cells (dry wt.)/mg S was estimated for both isomers of endosulfan. A mutant of Pseudomonas aeruginosa WSC was identified which had lost the ability to acquire sulfur from endosulfan while retaining an intact sulfur assimilation pathway. The isolation of this mutant would appear to eliminate the possibility that endosulfan was non-enzymatically degraded to endodiol and extracellular free sulfite by Ps. aeruginosa WSC. This mutant will also provide an important starting point in future work intended to investigate the gene(s) responsible for endosulfan detoxification.; In the third and final phase of research, the effect of selected environmental factors on the biotransformation capabilities of Ps. aeruginosa WSC were studied. Endosulfan was found to be only slightly toxic to the organism in the typical concentrations of endosulfan applied to agricultural fields (1 to 10 ppm), which suggests that endosulfan would be unlikely to exert severe toxicity pressures on the isolate at typical environmental concentrations. Biotransformation of endosulfan to endodiol was observed to be uninfluenced or slightly enhanced by the presence of alternative sulfur sources, which would suggest that the presence of usual environmental sulfur sources would not repress the detoxification activity of the microbe in environmental settings. Finally, the effect of sorption on bioavailability was investigated. Ps. aeruginosa WSC was observed to utilize endosulfan as a sulfur source when the insecticide was sorbed to soil particles: the limiting factor appeared to be available dissolved oxygen rather than the rate of endosulfan desorption from the soil. |
