Improved fermentative production of the compatible solute ectoine by Corynebacterium glutamicum from glucose and alternative carbon sources

•Ectoine production by Corynebacterium glutamicum with highest reported yield.•Avoidance of l-lysine export led to production of pure ectoine.•Ectoine production from alternative non-native carbon sources established.

The cyclic amino acid ectoine is a compatible solute serving as a protective substance against osmotic stress. Ectoine finds various applications due to its moisturizing effect. To avoid the disadvantages of the prevailing so-called “bacterial milking ectoine production process” caused by the high salt concentration, low salt fermentation strategies are sought after. As l-lysine and ectoine biosynthesis share l-aspartate-semialdehyde as common precursor, l-lysine producing strains can be converted to ectoine producing strains. Corynebacterium glutamicum, which is used for l-lysine production in the million-ton-scale, was engineered for ectoine production by heterologous expression of the ectoine biosynthesis operon ectABC from Chromohalobacter salexigens. Derepression of glucose metabolism by deletion of the regulatory gene sugR and avoiding l-lactate formation by deletion of the lactate dehydrogenase gene ldhA increased ectoine productivity. In bioreactor fed-batch cultivations an ectoine titer of 22 g L−1 and a volumetric productivity of 0.32 g L−1 h−1 were obtained. The ectoine yield of 0.16 g g−1, to the best of our knowledge, exceeded previously reported yields. Moreover, ectoine production from the alternative carbon sources glycerol, glucosamine, xylose, arabinose, and soluble starch was achieved.