The autolysin activity of B. thuringiensis strain was evaluated by the method of Raddadi et al. (2004) with a few modifications. Briefly, the cells grown in LB broth were harvested atOD600 1.2. The cells were washed inMES (2-Nmorpholino-ethansulfonic acid 50 mM, pH 6), resuspended in the same buffer, in potassium phosphate buffer (50 mM, pH 6.5) or Tris–HCl (50 mM, pH 8.5) buffers and incubated at 30C without agitation. The autolytic rate was expressed as the percentage decrease of the OD600 after 72 h. To evaluate hydrolase action of autolysins, commercially available substrate p-nitrophenyl-N-acetyl-b-D-glucosaminide (Sigma) and respective enzyme standard (b-N-acetylglucosaminidase of Canavalia ensiformis; Sigma) was used and assayed as described previously (Tsujii et al. 1996). In brief, 100 ll supernatant of SE strain was added in 50 mM phosphate buffer at pH 6.7 and incubated at 37C for 30 min. The enzymatic reaction was initiated by adding 0.5 mM p-nitrophenyl-N-acetyl-b-D-glucosaminide and incubated for 1 h at 37C. The reaction was stopped by adding three volumes of 1 M Na2CO3. Enzymatic activity was quantified by measuring the absorption at 405 nm and compared with standard curve of p-nitrophenol. One unit of hydrolase activity is defined as amount of enzyme converting 1.0 lmole of p-nitrophenyl-N-acetyl-b-D-glucosaminide to p-nitrophenol per min under the assay conditions.