Bacillus thuringiensis Cry2Ab is active on Anopheles mosquitoes: Single D block exchanges reveal critical residues involved in activity

Abstract

Cry2Aa exhibits dual activity to Lepidoptera and Diptera. Cry2Ab differs in amino acid sequence from Cry2Aa by 13% and has shown significant lepidopteran activity, but no mosquitocidal activity. Previous studies implicate 23 Cry2Aa specificity-conferring residues of domain II, which differ in Cry2Ab. Nine residues are putatively involved in conferring Cry2Aa dipteran specificity. To explore Cry2Ab dipteran toxicity, site-directed mutagenesis was employed to exchange Cry2Ab residues with Cry2Aa D (dipteran) block residues. Cry2Ab wild type demonstrated high toxicity (LC 50 of 540 ng mL -1) to Anopheles gambiae, but not to Aedes or Culex, within a 24-h time period. Cry2Ab should be reclassified as a dual active Cry toxin. Cry2Ab mutagenesis revealed critical residues for Cry2Ab protein function, as well as enhanced activity against the malarial mosquito, An. gambiae. © 2011 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved.