Abstract
A host-vector system was established in Lactobacillus helveticus with β-galactosidase activity as a selection marker. Plasmid pBG10 was constructed by joining the β-galactosidase gene from L. bulgaricus, the promoter region of the erythromycin resistance gene from pAMβ1, the replication region of pBR329, and the replication region the L. helveticus cryptic plasmid pLJ1. L. helveticus SBT2195 (Lacmutant), transformed with pBG10, was selected on skim milk plates. The structural gene of α-amylase (1536bp) from Bacillus licheniformis, inserted downstream of the promoter region of the erythromycin resistance gene of pBG10, was expressed in L. helveticus SBT2195. Plasmid pBG10 is a food-grade and expression vector in L. helveticus.
