CHARACTERIZATION OF BACTERIAL ISOLATES (Rhizobium leguminosarum and Bacillus thuringiensis) ABLE TO DEGRADE OF MALATHION AND METHOMYL PESTICIDES .

The symbiotic nitrogen fixing soil bacterium, Rhizobium leguminosarum bv. vicieae, is well known for its ability to interact with the leguminous plant Vicia faba. It has, however, not been reported that this species possesses the capability to degrade pesticides that are commonly associated with the agricultural processes. In this study the ability of R.leuminosarum bv.vicieae and the bioinsecticide B.thuringiensis bacteria  to degrade malathion and methomyl was investigated. Some mutants were have been isolated. Three mutants of Rhizobia were found to be resistant to malathion up to 7000 ppm(RF12 mal^r, RZ11 mal^r and RH11 mal^r). Bt mutants (Bt3 mal^r, Bt7 mal^r and Bt8 mal^r) were also resistant up to 7000 ppm. Methomyl resistant mutants (RF12 lan^r, RZ11 lan^r and Bt7 lan^r) were resistant up to 10.000 ppm. All these mutants were able to utilize malathion or methomyl as a sole carbon source. The yeast extract was observed to enhance bacterial growth rate in the presence of the two pesticides, Whereas, Cfu/ml was reached up to 9.78 x 10¹⁶ in Rhizohium and 9.84 x 10¹⁶ in Bt after 10 days of incubation time. Bacterial mutants did not lose the property to grow on media containing 7000 ppm malathion or 10.000 ppm methomyl after acridine orange mediated curing. Gene transfer by conjugation mechanism showed that degradative gene(s) was able to transfer among not only between strains but also between different genera. Transconjugants were able to resist and grow in malathion or methomyl containing media. Some transconjugants were found to be higher response to these pesticides than their parents. It has been suggested that malathion and methomyl degradation gene(s) of Rhizobium leguminosarum bv. vicieae and Bacillus thuringiensis are chromosomal harboring not plasmid genes.