Engineering microbial cell factories: Metabolic engineering of Corynebacterium glutamicum with a focus on non-natural products.

Corynebacterium glutamicum is the workhorse of biotechnological amino acid production. For more than 50 years amino acid producing strains of this actinomycete have been improved by classical breeding, metabolic engineering and systems and synthetic biology approaches. This review focusses mainly on recent developments on C. glutamicum strain development for non-natural products. Recently, metabolite sensors have accelerated classical strain breeding. Synthetic pathways for access to alternative carbon sources, such as pentoses, and to new products, such as α, ω-amino acids, α, ω-diamines, α-keto acids, isobutanol, carotenoids and terpenes, have been embedded in the central metabolism of C. glutamicum. Furthermore, C. glutamicum is a chassis for new and improved production processes that has been improved in two ways: by rendering it biotin prototrophic and by curing it from its prophage DNA followed by further genome reduction. The first combinations of this chassis approach with production will be highlighted. Although their transfer to industrial scale processes will have to be evaluated, these recent achievements indicate how synthetic biology helps realizing proof-of-principles. Moreover, current and future synthetic biology technology developments hold the promise to explore the full potential of C. glutamicum as production host for value-added chemicals.