Effect of saccharides on growth, sporulation rate and δ-endotoxin synthesis of Bacillus thuringiensis

Abstract

Effect of monosaccharides (glucose, fructose and galactose) and disaccharides (sucrose, lactose and maltose) as carbon sources on growth and sporulation rate of Bacillus thuringiensis MPK13 as well as δ-endotoxin production was investigated using 400 ml shake flasks culture. Substantially high growth and sporulation rate were obtained in cultivation using glucose and sucrose. Fructose, galactose, lactose and maltose were also able to support growth, but failed to enhance high sporulation rate. In general, high sporulation rate was related with high growth rate and high viable cell count (>1.5 x 10¹² cfu/ml). However, the presence of appropriate quantity of glucose was required to trigger δ-endotoxin formation. The presence of δ-endotoxin with molecular weight of 130 kD assayed using sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), was only detected after 48 h of cultivation using 8 g/L glucose as the sole carbon source. Although good growth with high spore production was obtained in cultivation using a mixture of glucose (4 g/L) with other sugars, the spores produced contained no endotoxin. The existence of δ-endotoxin was also observed in cultivation using a mixture of various sugars (fructose, sucrose, maltose and lactose) with 8 g/L glucose, indicating that high glucose (> 8 g/L) must be present in the culture to trigger δ-endotoxin formation in the spores of Bacillus thuringiensis MPK13.

Key words: Bacillus thuringiensis, saccharides, cell growth, sporulation rate, δ-endotoxin.