Abstract
To establish safety is most important when genetically-modified microorganisms like lactic acid bacteria are planned to apply for food production. For this reason, it would be necessary to use exclusively safe genetic materials which are suitable for food production, and also to guarantee the genetic stability and the safety of the genetically-improved microorganisms. The authors have tried to establish the fundamental techniques to construct safe recombinant strains of yogurt starters: Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus. So far two techniques have been established including a double cross-over, which ensures exclusive introduction of the objective gene in the host chromosome, and a host-vector system composed of only safe genetic materials. These results would be useful to establish safety of the future recombinant lactic acid bacteria to be used for food production.
