Cry3Aa11: A New Cry3Aa δ-Endotoxin from a Local Isolate of Bacillus thuringiensis

Insecticidal Activity of Bacillus thuringiensis Proteins Against Coleopteran Pests

Bacillus thuringiensis is the most successful microbial insecticide agent and its proteins have been studied for many years due to its toxicity against insects mainly belonging to the orders Lepidoptera, Diptera and Coleoptera, which are pests of agro-forestry and medical-veterinary interest. However, studies on the interactions between this bacterium and the insect species classified in the order Coleoptera are more limited when compared to other insect orders. To date, 45 Cry proteins, 2 Cyt proteins, 11 Vip proteins, and 2 Sip proteins have been reported with activity against coleopteran species. A number of these proteins have been successfully used in some insecticidal formulations and in the construction of transgenic crops to provide protection against main beetle pests. In this review, we provide an update on the activity of Bt toxins against coleopteran insects, as well as specific information about the structure and mode of action of coleopteran Bt proteins.

Characterization of a novel cry8 gene specific to Melolonthidae pests: Holotrichia oblita and Holotrichia parallela

A new polymerase chain reaction-restriction fragment length polymorphism method for the identification of cry8-type genes from Bacillus thuringiensis has been established by designing a pair of new universal primers. By this method, a novel gene, cry8Ga1, encoding a polypeptide of 1,157 amino acids with a deduced molecular mass of 131.2 kDa was identified and cloned from B. thuringiensis HBF-18. Recombinant B. thuringiensis strain HD8G, harboring cry8Ga1, has insecticidal activity against larvae of Melolonthidae pests: Holotrichia oblita and Holotrichia parallela. This is the first report of a Cry toxin that has insecticidal activity to Melolonthidae pest H. oblita.

Expression of chitinase A (chiA) gene from a local isolate of Serratia marcescens in Coleoptera-specific Bacillus thuringiensis

AIMS

The present study focused on cloning and expression of chiA gene from a highly chitinolytic local isolate of Serratia marcescens in an anti-Coleopteran Bacillus thuringiensis and comparison of the characteristics of the native and recombinant ChiAs.

METHODS AND RESULTS

chiA gene from Ser. marcescens was cloned, sequenced and compared with the previously cloned chiA genes. chiA gene was PCR cloned and expressed in anti-Coleopteran B. thuringiensis strain 3023 as verified by Western blot analysis. Specific ChiA activity of the recombinant B. thuringiensis (strain 3023-SCHI) reached its highest level at 21st hour of growth (16.93 U mg(-1)), which was 5.2- and 1.3-fold higher than that of its parental strain and Ser. marcescens, respectively. Temperature and pH effects on native and recombinant ChiAs were next determined. The recombinant plasmid was quite stable over 240 generations.

CONCLUSIONS

Serratia marcescens ChiA was heterologously expressed in an anti-Coleopteran B. thuringiensis at levels even higher than that produced by the source organism.

SIGNIFICANCE AND IMPACT OF THE STUDY

Bacillus thuringiensis 3023-SCHI co-expressing anti-Coleopteran Cry3Aa protein and Ser. marcescens chitinase offers a viable alternative to the use of chitinolytic microbes/enzymes in combination with entamopathogenic bacteria for an increased potency because of synergistic interaction between them.