Abstract
The efficiency of industrial fermentation process mainly depends on carbon yield, final titer and productivity. To improve the efficiency of l-lysine production from mixed sugar, we engineered carbohydrate metabolism systems to enhance the effective use of sugar in this study. A functional metabolic pathway of sucrose and fructose was engineered through introduction of fructokinase from Clostridium acetobutylicum. l-lysine production was further increased through replacement of phosphoenolpyruvate-dependent glucose and fructose uptake system (PTSGlc and PTSFru) by inositol permeases (IolT1 and IolT2) and ATP-dependent glucokinase (ATP-GlK). However, the shortage of intracellular ATP has a significantly negative impact on sugar consumption rate, cell growth and l-lysine production. To overcome this defect, the recombinant strain was modified to co-express bifunctional ADP-dependent glucokinase (ADP-GlK/PFK) and NADH dehydrogenase (NDH-2) as well as to inactivate SigmaH factor (SigH), thus reducing the consumption of ATP and increasing ATP regeneration. Combination of these genetic modifications resulted in an engineered C. glutamicum strain K-8 capable of producing 221.3 ± 17.6 g/L l-lysine with productivity of 5.53 g/L/h and carbon yield of 0.71 g/g glucose in fed-batch fermentation. As far as we know, this is the best efficiency of l-lysine production from mixed sugar. This is also the first report for improving the efficiency of l-lysine production by systematic modification of carbohydrate metabolism systems.
Highlights
The efficiency of industrial fermentation process mainly depends on carbon yield, final titer and productivity
In order to improve the efficiency of l-lysine production from mixed sugar, we focused on the genetic modification of genes involved in carbohydrate metabolism systems to increase the l-lysine productivity of C. glutamicum K-1
Hetero-expression of ScrK from C. acetobutylicum at pfkB gene loci was set as a potential strategy for enhancing l-lysine production on mixed sugar in this study
Summary
The efficiency of industrial fermentation process mainly depends on carbon yield, final titer and productivity. The recombinant strain was modified to co-express bifunctional ADP-dependent glucoki‐ nase (ADP-GlK/PFK) and NADH dehydrogenase (NDH-2) as well as to inactivate SigmaH factor (SigH), reducing the consumption of ATP and increasing ATP regeneration Combination of these genetic modifications resulted in an engineered C. glutamicum strain K-8 capable of producing 221.3 ± 17.6 g/L l-lysine with productivity of 5.53 g/L/h and carbon yield of 0.71 g/g glucose in fed-batch fermentation. PTS uses phosphoenolpyruvate (PEP) as phosphoryl group donor, resulting in the low intracellular PEP and the increase of flux through PEP carboxykinase [14] It is a problem for realizing the efficient production of l-lysine that how to balance carbohydrate uptake capacity and carbohydrate consumption rate. This gives us a positive reference to construct l-lysine high-producing strain to improve the efficiency of l-lysine production
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