EVALUATION OF AN RIBOSOMAL-RNA-TARGETED OLIGONUCLEOTIDE PROBE FOR THEDETECTION OF MOSQUITOCIDAL STRAINS OF BACILLUS-SPHAERICUS IN SOILS - CHARACTERIZATION OF NOVEL STRAINS LACKING TOXIN GENES

Colonies of Bacillus sphaericus on primary isolation have been identif ied using an oligonucleotide probe targeted to a specific region of th e 16S rRNA, Of 3440 colonies from soil Samples from Brazil, 57 hybridi zed to the probe in colony blots but when purified DNA was used in slo t-blots the probe was more specific and only 27 isolates hybridized. O f these, 20 strains were confirmed as members of DNA homology group II A (potential mosquitocidal Strains) by ribotyping and isoenzyme analys is. However, none of these strains was toxic to Anopheles or Culex lar vae, nor did they contain recognized toxin genes. This is the first de monstration of such nan-pathogenic strains of B. sphaericus DNA homolo gy group IIA aad their common occurrence suggests that pathogenicity i s not an important contribution to the success of these bacteria in th e environment. Similar screening of strains from Scottish soils indica ted that B. sphaericus DNA homology group IIA strains were less common in this habitat and none were recovered on this occasion.