Novel insecticidal toxins from nematode-symbiotic bacteria

The current strategy of using transgenic crops expressing insecticidal prot ein toxins is placing increasing emphasis on the discovery of novel toxins, beyond those already derived from the bacterium Bacillus thuringiensis. He re we review the cloning of four insecticidal toxin complex (tc) encoding g enes from a different bacterium Photorhabdus luminescens and of similar gen e sequences from Xenorhabdus nematophilus. Both these bacteria occupy the g ut of entomopathogenic nematodes and are released into the insect upon inva sion by the nematode. In the insect the bacteria presumably secrete these i nsecticidal toxins, as well as a range of other antimicrobials, to establis h the insect cadaver as a monocultural breeding ground for both bacteria an d nematodes. In this review, the protein biochemistry and structure of the tc encoding loci are discussed in relation to their observed toxicity and h istopathology. These toxins may prove useful as alternatives to those deriv ed from B. thuringiensis for deployment in insect-resistant transgenic plan ts.