Engineering of klebsiella oxytoca for simultaneous utilization of mixed sugars from microalgae hydrolysate

Abstract

Microalgae have been mainly used for the production of bio-diesel because of its high lipid content. In the actual process using microalgae, large amounts of the residue are generated. After the acid saccharification process, the mixed sugars are obtained from microalgae residue and bio system can be constructed with Klebsiella oxytoca, which can produce 2,3-butanediol (2,3-BDO) by using the various carbon sources. However, the consumption of other sugars except glucose was delayed because of the carbon catabolite repression (CCR). It reduces the growth rate of K. oxytoca and productivity of 2,3-BDO. To solve this problem, K. oxytoca was engineered for simultaneous utilization of mixed sugars. Galactose transporter protein (galP) was introduced into K. oxytoca, so that galactose was always consumed regardless of glucose concentration. Also, I controlled the expression level of protein by using the constitutive synthetic promoter, because the overexpression of sugar transporter protein may decrease the viability of the cells. Through this engineering of K. oxytoca, I achieved the increase of consumption rate of mixed sugars and productivity of 2,3-BDO. Also, it was confirmed that the sugar metabolism efficiency was increased by removing the mgsA gene of K. oxytoca, which is involved in the production of methylglyoxal, the inhibitor of sugar metabolism.