Characteristics of new bacillus thuringiensis strains isolated From soils in the vicinity of the Baekdu mountain and biological activity against Spodoptera exigua

From among 16 B. thuringiensis strains collected and isolated from soils in the vicinity of the Baekdusan mountain, four strains (YN1-1, YN2-6, YN4-2, and YN6-2) that showed high LC95 values for Spodoptera exigua. 3rd larvae of 2.43 × 10⁶, 7.00 × 10⁶, 3.26 × 10⁶, and 2.62 × 10⁶ cfu/ml, respectively, were finally selected. SDS-PAGE experiments were conducted to identify the toxoprotein patterns of the new four strains and, in the results, all the strains showed major bands of ca. 130 kDa, which were changed into ca. 65 kDa through digestion by Spodoptera exigua midgut fluid. To identify the Cry gene compositions of the strains, plasmid DNAs were extracted and PCR was conducted using specific primers (crylAa-crylL). Six genes (crylAa, crylAb, crylC, crylD, cryll and crylL) were identified in three strains: YN1-1, 2-6, and 4-2 and the amplification of five genes; crylAa, crylAc, crylC, crylD and crylL in the YN6-2 strain. All four B. thuringiensis strains were identified as B. thuringiensis subsp. aizawai strains by comparing the H serotypes of 16S rRNA and flagellin (fliC) gene. The possibility of commercialization of YN1-1 strain was examined by insecticidal activity test for the Spodoptera exigua 3rd larvae of six B. thuringiensis pesticide products sold in Korea.