Metabolic engineering was used with Corynebacterium glutamicum to increase the rate of lysine synthesis.
(a) Branchpoint engineering allows more metabolic flux to be directed down one branch of the pathway, reducing the synthesis of an undesired product. This also allows more efficient use of the limited supply of energy the cell has.
(b) By optimising cofactor supply, the concentration of cofactors can be increased to allow for greater flux through previously limiting factors in the pathway. This was used to engineer higher levels of lysine synthesis in Corynebacterium glutamicum, increasing the concentration of NADPH for the transhydrogenase reaction.
(c) Increasing product efflux also allows for an improvement in synthesis of lysine. At high levels, lysine is toxic to Corynebacterium glutamicum. Therefore, efflux is necessary to maintain the fermentation. Controlled overexpression of LysE (a lysine exporter) allows for the correct balance of lysine efflux. This makes it easier to recover the lysine, as it can simply be extracted from the growth media, instead of having to lyse the cells.
These three processes allowed for a very large increase in lysine synthesis, reaching 180 grams per Litre of fermentation. This makes it much more economical to synthesise lysine, as well as reducing costs to patients and in animal feeds.