Restriction map of large plasmid pFW1 in Bacillus sphaericus strain 10

Some strains of Bacillus sphaericus have been found to be toxic to mosquito larvae (1). They differ from Bacillus thuringiensis var. israelensis (BTI) (2,3) in the following aspects: BTI is relatively ineffective in polluted water, and its residual activity in most habitats is limited to a few days after treatment, whereas BS isolates are effective in such habitats, particularly against species of Culex; BS also remains effective longer, as a result of either persistence or recycling. B. sphaericus strain 10 (BS10) was isolated by the Lixiahe Institute of Agricultural Sciences in Jiangsu Province. Its larvicidal activity is much higher than that of BS1593, which was recommended by the World Health Organization for widespread use as a standard strain (1). The mosquito-larvicide gene of BS1593 has been cloned and expressed in E. coli and B. subtilis (4, 5). In the present study, BS10 was investigated to establish whether it contains the plasmid and whether homology exists between the mosquito-larvicide gene in BS and that in BTI.