GLUTATHIONE-S-TRANSFERASE ACTIVITY IN RHIZOSPHERE BACTERIA AND THE POTENTIAL FOR HERBICIDE DETOXIFICATION

Glutathione S-transferase (GST; EC 2.5.1.18) activity was found in isolates of Gram-negative rhizobacteria, especially Pseudomonadaceae and Enterobacteriaceae. GST-mediated dechlorination of chlorodinitrobenzene and the herbicide alachlor and GST-mediated cleavage of the ether bond of the herbicide fluorodifen was observed for some strains. No atrazine-GST activity was found. Certain fluorescent pseudomonads can dechlorinate 75 to 100 mu M alachlor in 48 to 96 h with the cysteine conjugate as the major accumulating intermediate. Levels of alachlor-GST catabolism observed in native rhizosphere communities were lower than most Pseudomonas fluorescens strains identified in this work. Activities of gamma-glutamyltranspeptidase (EC 2.3.2.2), and cysteine-beta-lyase (EC 4.4.1.6 and 8) enable a rapid metabolism of glutathione-conjugates. Rhizosphere-competent bacteria selected for high GST activity and downstream catabolism may have potential as seed/soil inoculants in bioremediation/detoxification of certain herbicides or other xenobiotics.