CONSTRUCTION OF FOOD-GRADE MUTANTS OF LACTIC-ACID BACTERIA

Selection of reliable starter strains is an important objective for da iry industries. The present industrial approach is to isolate a strain at random by screening a collection of natural isolates. More recent advances in genetic technology may give rise to more direct strategies for strain selection. To this end, we have constructed genetic tools based on two natural processes: homologous recombination and transposi tion. Using these tools, we can: i) identify and modify genes involved in a bacterial process; ii) construct food-grade mutants, ie, genetic ally modified strains with no trace of foreign DNA; and iii) extend th is modification to other related bacteria. The engineered strain has t he advantage that its improved properties are well defined and can be reproduced. Food-grade mutants represent a real potential to answer so me of the industrial problems concerning starter technology.