Characterization of Bacillus thuringiensis strain Bt185 toxic to the Asian cockchafer: Holotrichia parallela.

A new Bacillus thuringiensis strain, Bt185, was isolated from HeBei soil samples in China. Observations after transmission electron microscopy found that the strain produced spherical parasporal inclusions similar to that of the B. thuringiensis subsp. japonensis Buibui strain, which showed toxicity to both Anomala corpulenta and Popillia japonica. The plasmid profile seen on an agarose gel revealed that Bt185 contained six large bands of 191 kb, 161 kb, 104 kb, 84 kb, 56 kb, and 37 kb. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis revealed one major band with an estimated molecular mass of 130 kDa. Polymerase chain reaction-restriction fragment length polymorphism results showed that a novel cry8-type gene sequence was found in the Bt185 strain. When we screened for this novel gene sequence, an additional novel cry8-type gene was isolated, having a partial sequence of 2340 bp and encoding a protein of 780 amino acids. Bioassay results showed that Bt185 had no toxicity against several Coleopteran and Lepidopteran pests. However, Bt185 exhibited toxicity against larvae of the Asian cockchafer, Holotrichia parallela. This is the first report of the occurrence of a Bacillus strain that has insecticidal activity against Holotrichia parallela larvae.