Journal
ANNALS OF MICROBIOLOGY
Volume 63, Issue 3, Pages 1131-1135Publisher
SPRINGER
DOI: 10.1007/s13213-012-0570-0
Keywords
Bacillus thuringiensis; Host; Melanin; Ultraviolet radiation; Biopesticide
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The bacterium Bacillus thuringiensis produces a crystal protein with insecticidal properties; however, crystal proteins can be damaged by ultraviolet (UV) radiation. The aim of this study was to improve the stability of the insecticidal crystal protein (ICP) by constructing a mutant line that expresses high levels of the UV light-protecting pigment, melanin. BMB181, a B. thuringiensis mutant with high melanin production, was obtained after sub-culturing BMB171 for several generations at 42 A degrees C. The melanin yield by BMB181 (without tyrosine supplementation) reached 8.55 mg/ml. The electroporation efficiency of BMB181 reached 10(6) CFU/mu g when a 6.7-kb foreign plasmid was used. Microscopic and SDS-PAGE analyses revealed that ICP (CryIAc10; GenBank: AAA73077.1), which is highly toxic to Lepidoptera, was synthesized efficiently by strain BMB181. The insecticidal properties of a recombinant line derived from strain BMB181, designated BMB32 (cry1Ac10/BMB181), was tested against the cotton bollworm, Helicoverpa armigera. After UV irradiation for 4 h, BMB32 had a half maximal inhibitory concentration value of 1.37 mu g/ml, whereas the control line BMB31 (cry1Ac10/BMB171) had a median lethal dose value of 25.85 mu g/ml. These results indicate that the B. thuringiensis mutant is a candidate for industrial scale production of light-stable insecticides.
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