DDT-resistance inAnopheles gambiae(Diptera: Culicidae) from Zanzibar, Tanzania, based on increased DDT-dehydrochlorinase activity of glutathione S-transferases

Abstract

AbstractDDT-resistantAnopheles gambiaeGiles from Zanzibar, Tanzania, had increased levels of DDT-dehydrochlorination compared to a DDT-susceptible strain. Glutathione S-transferases (GSTs) are responsible for conversion of DDT to DDE in both the susceptible and resistant strains. Sequential column chromatography, including Q-Sepharose, S-hexylglutathione agarose, hydroxylapatite and phenyl Sepharose, allowed the partial purification of seven GSTs. All seven GSTs possessed different degrees of DDTase activity. There was an eight-fold increase in total DDTase activity in the resistant compared to the susceptible enzymes. Characterization with three substrates, 1-chloro-2,4-dinitrobenzene (CDNB), 1,2-dichloro-4-nitrobenzene (DCNB) and DDT, revealed the different substrate specificity for each isolated GST indicating different isoenzymes. GST Va possessed 60% of total DDTase activity suggesting that it contributed most to DDT-metabolism in this insect species. The DDTase activity of the GSTs in both strains ofA. gambiaewere found to be correlated with the GST activities toward DCNB. Preliminary studies on DDT-resistant and susceptibleA. gambiaeshowed that both DDT-resistance and the increased levels of GST activity were stage specific which suggested that different GSTs may be involved in DDT-resistance in adults and larvae ofA. gambiae.