Distribution of Bacillus thuringiensis in forest soil of Hokkaido

Abstract

Specimens from wild strains of Bacillus thuringiensis were collected from 200 partitioned survey sites in each of the following two places and were examined for the morphology of parasporal inclusions (PI) under a scanning electron microscope and for the H antigen distribution by an immunological method. The results are summarized as follows. 1) In an area in the Nohoro Forest Park, a representative lowland of the Hokkaido forest, 39 strains of B. thuringiensis were isolated from 17 (8.5%) of the 200 sampling sites. At 14 of the 17 sites, the density was as low as one strain per sampling site. The isolated strains were comprised of four H antigen types: 5a5b, 16, 4a4c and 14. H antigen type 5a5b was dominant, occupying about 61% of the total strains. All strains were one of five types in terms of parasporal inclusion morphology: bipyramidal & cuboidal, bipyramidal & cuboidal & irregular, irregular and cuboidal. The strain named IL1-7-2 was incapable of producing bipyramidal parasporal inclusions, but it produces a remarkably large quantity of cuboidal parasporal inclusions and was considered to be of a new type different from the type serovars. 2) In an open-air chapel of Rakuno Gakuen University, wherein trees are well conserved, 70 strains of B. thuringiensis were isolated from 26 (13%) of the 200 survey sites. At 24 of the 26 sites, the density was as low as four or fewer strains per area. The isolated strains were comprised of 11 H antigen types: 1, 3a3b, 4a4b, 5a5b, 6, 7, 8a8b, 10, 14, 16 and 24a24b. Again the H antigen type 5a5b was dominant, occupying about 60% of the total strains. As to the parasporal inclusion morphology, all strains were one of seven types, including collapsed bipyramidal and collapsed cuboidal. The strains named MR10-3-3, MR10-5-1, MRIO-5-2, MRIO-5-3, MR10-6-2 and ML4-2-1 were incapable of producing bipyramidal parasporal inclusion, but only produce cuboidal parasporal inclusion and were thus considered to be of a new type different from the type serovar.