Purification and characterization of the larvicidal toxin of Bacillus sphaericus 1593M

We present here a procedure for purifying the larvicidal toxin from sporulating cells of Bacillus sphaericus 1593M and describe some of the biochemical and biophysical properties of this toxin. The procedure involves solubilization of the cell-wall/membrane bound toxin by sonication of cells followed by repeated rounds of freezing and thawing at 50°C. Further purification involved Sephadex G-100 and DEAE Sephacel chromatography. We show by Sephadex G-100 chromatography that at pH 7.5 the smallest active form of the toxin has an Mr of 38,000 and that this toxin can reversibly aggregate to molecular forms of a size higher than 2×105 Mr. By shifting the pH from 7.5 to 8.5 only the aggregated forms can be observed.