Expression of the <Emphasis Type="BoldItalic">Escherichia coli pntAB</Emphasis> genes encoding a membrane-bound transhydrogenase in <Emphasis Type="BoldItalic">Corynebacterium glutamicum</Emphasis> improves <Emphasis Type="SmallCaps">l</Emphasis>-lysine formation

A critical factor in the biotechnological production of l-lysine with Corynebacterium glutamicum is the sufficient supply of NADPH. The membrane-integral nicotinamide nucleotide transhydrogenase PntAB of Escherichia coli can use the electrochemical proton gradient across the cytoplasmic membrane to drive the reduction of NADP⁺ via the oxidation of NADH. As C. glutamicum does not possess such an enzyme, we expressed the E. coli pntAB genes in the genetically defined C. glutamicum lysine-producing strain DM1730, resulting in membrane-associated transhydrogenase activity of 0.7 U/mg protein. When cultivated in minimal medium with 10% (w/v) carbon source, the presence of transhydrogenase slightly reduced glucose consumption, whereas the consumption of fructose, glucose plus fructose, and, in particular, sucrose was stimulated. Biomass was increased by pntAB expression between 10 and 30% on all carbon sources tested. Most importantly, the lysine concentration was increased in the presence of transhydrogenase by ∼10% on glucose, ∼70% on fructose, ∼50% on glucose plus fructose, and even by ∼300% on sucrose. Thus, the presence of a proton-coupled transhydrogenase was shown to be an efficient way to improve lysine production by C. glutamicum. In contrast, pntAB expression had a negative effect on growth and glutamate production of C. glutamicum wild type.