Abstract
Background: 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 great potentials to increase the production of L-lysine. Results: The aim of this work is to enhance the carbon flux in dehydrogenase pathway to promote L-lysine production. Firstly, 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 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 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. Conclusions: 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.
Structural basis for redox sensitivity in Corynebacterium glutamicum diaminopimelate epimerase: an enzyme involved in l-lysine biosynthesis
