Gene dosage effect on the expression of the delta-endotoxin genes of Bacillus thuringiensis subsp. kurstaki in Bacillus subtilis and Bacillus megaterium

Significant differences in expression of the delta-endotoxin genes cryA1 and cryA2 of Bacillus thuringiensis subsp. kurstaki were observed in B. subtilis and B. megaterium. The cryA1 gene was expressed when present on a high-copy-number (hcn) vector in B. megaterium but not in B. subtilis. The cryA2 gene was expressed in both hosts, but at a higher level in B. megaterium. Expression of the cryA2 gene in B. megaterium was better from a hcn vector than from a low copy number vector. Inhibition of sporulation was observed when the toxin genes were present on hcn plasmids in B. subtilis while no such effect was evident in B. megaterium. In addition, there was a significant reduction in copy numbers in both B. subtilis and B. megaterium when delta-endotoxin genes or a spoVG promoter-containing fragment of DNA were cloned into hcn plasmids.