GLUTATHIONE-S-TRANSFERASE ACTIVITY AND METABOLISM OF GLUTATHIONE CONJUGATES BY RHIZOSPHERE BACTERIA

Glutathione-S-transferase (GST) activity was determined in 36 species of rhizosphere bacteria with the substrate 1-chloro-2,4-dinitrobenzene (CDNB) and in 18 strains with the herbicide alachlor. Highest levels of CDNB-GST activity (60 to 222 nmol . h(-1) . mg(-1)) were found in g ram-negative bacteria: Enterobacter cloacae, Citrobacter diversus, Kle bsiella planticola, Pseudomonas cepacia, Pseudomonas fluorescens, Pseu domonas putida, and Xanthomonas campestris. There was very low CDNB-GS T activity in the gram-positive strains. Rapid metabolism of CDNB-glut athione conjugates, attributable to high levels of gamma-glutamyltrans peptidase, also occurred in the gram-negative bacteria, especially pse udomonads. Alachlor-GST activity detected in cell extracts and whole-c ell suspensions of some strains of the families Enterobacteriaceae and Pseudomonaceae was 50- to 100-fold lower than CDNB-GST activity (0.5 to 2.5 nmol . h(-1) . mg(-1)) and was, for the most part, constitutive . The glutathione-alachlor conjugate was rarely detected. Cysteineglyc ine and/or cysteine conjugates were the major products of alachlor-GST metabolism. Whole-cell suspensions of certain Pseudomonas spp, dechlo rinated from 20 to 75% of 100 mu M alachlor in 24 h. Results indicate that rhizosphere bacteria, especially fluorescent pseudomonads, may pl ay an important role in the degradation of xenobiotics such as alachlo r via GST-mediated reactions.