Mosquitocidal activity of a native Bacillus thuringiensis isolate Bt ReX02 from Gunung Jerai Forest, Malaysia against Culex quinquefasciatus and Aedes albopictus

A. Prazanna Lakxmy, R. Xavier, C.M. Reena Josephine, Y.W. Lee*, K. Marimuthu, S. Kathiresan, S. Sreeramanan**

Department of Biotechnology, Faculty of Applied Sciences, Aimst University, Semeling, Kedah Darul Aman (Malaysia) *Coopers Lifesci Sdn-Bhd-WellTech Health care Group, Kuala Lumpur (Malaysia) **School of Biological sciences, Universiti Sains Malaysia (USM), Penang (Malaysia)

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• Infectious Diseases

Background and Objective: To evaluate the mosquito larvicidal potential of the native Bacillus thuringiensis isolate BtReX02, which was isolated from a tropical rain forest ecosystem in Malaysia. This study also aimed at determining the phenotypic and biochemical characteristics of the isolate.

Materials and Methods: The phenotypic characterization was carried out by growing the isolate in nutrient broth to observe the colonial morphology, vegetative cells, sporulation, motility and haemolytic activity. The parasporal crystal morphology was determined by Coomassie Brilliant Blue (CBB) staining of the sporulated cells and then observed under light microscope.
The mosquito larvicidal assay was conducted with the second instar larvae of Culex quinquefasciatus and Aedes albopictus to determine the entomocidal potency of the isolate. The total protein profile was determined by SDS-PAGE.

Results and Discussion: Preliminary phenotypic and biochemical characterization showed that the isolate is motile, an indirect indication of the virulence of the strain and exhibited hemolytic activity, an important feature of antidipteran Bacillus thuringiensis strains. Study on the crystal morphology showed the presence of cuboidal crystals, another characteristic feature of a mosquitocidal Bacillus thuringiensis strains. Bioassay with the second instar larvae of Culex quinquefasciatus, Aedes albopictus established the antidipteran activity of this native Bacillus thuringiensis isolate. Protein profile analysis revealed the unique pattern showing high molecular mass as well as low molecular mass proteins corresponding to the Cry and Cyt proteins respectively. The protein profile is strikingly different from other mosquitocidal strains such as Bacillus thuringiensis subsp.israelensis and Bacillus thuringiensis subsp. jegathesan.
Periodical introduction of such native strains of Bacillus thuringiensis will add a new weapon in the armoury to manage the vector borne diseases and also in the management of insect resistance.

Corresponding Author: Rathinam Xavier, Ph.D; e-mail: rxavier77@yahoo.com

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