Propionibacterium freudenreichii is a commercially important bacterium that is used in the production of cheeses, cobalamin (vitamin B12) and propionic acid. Metabolic engineering using genetically improved strains will make the fermentation process more economical and also enhance the quality of the products. Host-vector systems and expression vectors using strong promoters from P. freudenreichii were developed in propionibacteria. By using these expression vectors and amplification of various genes, productions of 5-aminolevulinic acid, tetrapyrrole compounds and vitamin B12 were reported. Here, we review the advancement of genetic engineering in P. freudenreichii in recent years, covering the molecular aspects of the formation of tetrapyrrole compounds and vitamin B12.
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