Diversity of Bacillus thuringiensis strains from soil in China and their pesticidal activities

A large number of Bacillus thuringiensis (Bt) isolates have been obtained from soil samples in China. The flagellar antigen serotypes, cry genes and crystal proteins of 570 Bt isolates were determined, and the pesticidal activity was assayed against the insects, Plutella xylostella, Heliothis armigera, Phaedon brassicae and Locusta migratoria manilensis, and the snail, Oncomelania hupensis. The results indicated that the Bt isolates were distributed within 35 H-serotypes, in which isolates of H3 were the most abundant (20%) followed by H5 (13%), H7 (9%) and H4 (8.7%), whereas isolates of other H-serotypes were less than 6%. The percentage of isolates containing the genes cry1Ac, cry1Aa/cry1Ac, cry1Aa/cry1Ac/cry1Ab, and cry1Aa/cry1Ac/cry1C was 14.7%, 6.6%, 5.6%, and 7.0%, respectively, while 265 isolates, representing 46.5% of the 570 Bt isolates, did not show any amplification product for the genes cry1Aa, cry1Ac, cry1C, cry2, cry3, cry4, cry7Aa. Some of the 570 Bt isolates caused high mortality of the assayed pests with 14.9%, 6%, 1.6%, 1.1%, and 0.2% of the isolates killing more than 90% of P. xylostella, H. armigera, P. brassicae, O. hupensis, and L. migratoria manilensis, respectively. The remaining 76.2% of the 570 isolates caused no mortality or less than 90% mortality against the tested insect and snail species.