Immobilization in alginate as a new technique for the separation of Bacillus thuringiensis var. israelensis spore crystal complex

Abstract

Bacillus thuringiensis var. israelensis (Bti) spore crystal complex (SCC) produced by fermentation has to be separated before use for mosquito control in the breeding habitats. In this paper we report the development of a novel immobilization technique using sodium alginate as a matrix to separate the SCC of Bti and compared with acid precipitation method. Two strains of Bti VCRC B-17 and WHO standard strain IPS-82 were tested. Wet biomass yield of VCRC B-17 and IPS-82 separated by acid precipitation method was 215 and 224g/L, respectively, whereas by alginate immobilization method it was 258 and 270g/L, respectively. Spore yield of the respective strains, by acid precipitation method was 1.87×1014 and 2.17×1014CFU/mL, whereas by alginate immobilization method 2.3×1015 and 3.0 x 1015CFU/mL, respectively. Lethal concentration (LC50) of SCC of VCRC B-17 and IPS-82 by acid precipitation method was 1.18nl/mL and 0.92nl/mL, respectively, whereas LC50 values by alginate immobilization method was 0.94nl/mL and 0.71nl/mL, respectively. In the case of industrial substrate soya medium the yield of wet biomass, spore count and lethal concentration of VCRC B17 obtained by acid precipitation and alginate immobilization method were 311 and 360g/L, 1.40×1014 and 2.07×1015CFU/mL and 1.22 and 0.95nl/mL, respectively. Protease activity measured after acid precipitation and alginate immobilization method was 10.8 and 103.67U/mL, respectively. The international toxic units (ITU) of the VCRC B-17 by acid precipitation and alginate immobilization method were 13,636 and 13,888ITU/mg, respectively. Thus the alginate immobilization method has potential application in the harvesting and formulation of biopesticides.