Metabolic engineering of folate production in lactic acid bacteria

Folate is an essential compound in the human diet. Folate deficiency occurs frequently among certain population groups even in highly developed countries and may increase the risks for several diseases like neural tube defects, cardiovascular diseases and certain forms of cancer. The dairy starter bacterium Lactococcus lactis is able to synthesize this vitamin. The use of metabolic engineering has enabled the generation of a L. lactis strain with a more than 50-fold increased folate production. The synthesis of polyglutamyl folates and the associated release or retention of folate from or in the bacterial cell could be controlled by the expression levels of genes involved in folate biosynthesis and by the culture conditions. Moreover, the formation of monoglutamyl folate from polyglutamyl folate could enhance the bioavailability of folate, because folate is mainly consumed in the monoglutamyl form. In this thesis, we present the first animal trial on bioavailability of folates produced by genetically modified lactic acid bacteria. The outcome of this experiment forms the basis for a human clinical trial with these bacteria. Transformation of the entire folate gene cluster to a folate auxotroph Lactobacillus gasseri led to the production of folate in this bacterium and opens new avenues for the food industry to increase folate levels in fermented products. Further research on the production of vitamins in lactic acid bacteria has resulted in the development of a multivitamin producing L. lactis strain with increased production of folate and riboflavin. Such multivitamin producing strains could contribute to the development of nutrigenomics, facilitating a tailor made diet for individuals that have specific requirements for these two vitamins due to a genetic polymorphism.