Abstract
The dehydrogenase pathway and the succinylase pathway are involved in the synthesis of L-lysine in Corynebacterium glutamicum. Despite the low contribution rate to L-lysine production, the dehydrogenase pathway is favorable for its simple steps and potential to increase the production of L-lysine. The effect of ammonium (NH4+) concentration on L-lysine biosynthesis was investigated, and the results indicated that the biosynthesis of L-lysine can be promoted in a high NH4+ environment. In order to reduce the requirement of NH4+, the nitrogen source regulatory protein AmtR was knocked out, resulting in an 8.5% increase in L-lysine production (i.e., 52.3 ± 4.31 g/L). Subsequently, the dehydrogenase pathway was upregulated by blocking or weakening the tetrahydrodipicolinate succinylase (DapD)-coding gene dapD and overexpressing the ddh gene to further enhance L-lysine biosynthesis. The final strain XQ-5-W4 could produce 189 ± 8.7 g/L L-lysine with the maximum specific rate (qLys,max.) of 0.35 ± 0.05 g/(g·h) in a 5-L jar fermenter. The L-lysine titer and qLys,max achieved in this study is about 25.2% and 59.1% higher than that of the original strain without enhancement of dehydrogenase pathway, respectively. The results indicated that the dehydrogenase pathway could serve as a breakthrough point to reconstruct the diaminopimelic acid (DAP) pathway and promote L-lysine production.
Highlights
L-lysine is an essential amino acid widely used in food, animal feed, medicine, cosmetics, and other industries [1]
Algae, fungi, plants, and bacteria [6], the diaminopimelic acid (DAP) pathway starts with the biosynthesis of L-∆1 -tetrahydrodipicolinate (THDPA) from L-aspartate, which is converted into meso-DAP, and L-lysine is produced with diaminopimelate deacetylase
DAP pathway was reconstructed to optimize L-lysine production in C. glutamicum, which demonstrated that the dehydrogenase pathway is promising for promoting L-lysine production
Summary
L-lysine is an essential amino acid widely used in food, animal feed, medicine, cosmetics, and other industries [1]. L-lysine is mainly produced by microbial fermentation in the industries, with C. glutamicum and Escherichia coli being the most commonly used strains [1]. The L-lysine biosynthesis includes two pathways, the diaminopimelic acid (DAP). In the AAA pathway, L-lysine is synthesized from α-ketoglutarate and acetylcoenzyme A (acetyl-CoA) in which α-aminoadipic acid serves as an intermediate metabolite. In the DAP pathway, L-lysine is synthesized from aspartate and pyruvate in which meso-diaminopimelic acid (meso-DAP) serves as an intermediate metabolite (Figure 1) [5]. Algae, fungi, plants, and bacteria [6], the DAP pathway starts with the biosynthesis of L-∆1 -tetrahydrodipicolinate (THDPA) from L-aspartate, which is converted into meso-DAP, and L-lysine is produced with diaminopimelate deacetylase
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