Abstract
Dehydrogenase pathway, one of diaminopimelate pathway, is important to the biosynthesis of L-lysine and peptidoglycan via one single reaction catalyzed by meso-diaminopimelate dehydrogenase (DapDH). In this study, the thermostable DapDH was introduced into diaminopimelate pathway that increased the final titer (from 71.8 to 119.5 g/L), carbon yield (from 35.3% to 49.1%) and productivity (from 1.80 to 2.99 g/(L∙h)) of L-lysine by LATR12-2∆rpiB::ddhSt in fed-batch fermentation. To do this, the kinetic properties and the effects of different DapDHs on L-lysine production were investigated, and the results indicated that overexpression of StDapDH in LATR12-2 was beneficial to construct an L-lysine producer with good productive performance because it exhibited the best of kinetic characteristics and optimal temperature as well as thermostability in reductive amination. Furthermore, ammonium availability was optimized, and found that 20 g/L of (NH4)2SO4 was the optimal ammonium concentration for improving the efficiency of L-lysine production by LATR12-2∆rpiB::ddhSt. Metabolomics analysis showed that introducing the StDapDH significantly enhanced carbon flux into pentose phosphate pathway and L-lysine biosynthetic pathway, thus increasing the levels of NADPH and precursors for L-lysine biosynthesis. This is the first report of a rational modification of diaminopimelate pathway that improves the efficiency of L-lysine production through overexpression of thermostable DapDH in E. coli.
Highlights
L-lysine, one of the essential amino acids for animals and humans[1], is widely used in feed, food, and pharmaceutical industry, etc
We introduced a diaminopimelate dehydrogenase (DapDH) from different bacteria with different temperature optimum in E. coli to investigate its effect on L-lysine production; results indicated that the DapDH from thermophilic bacterium S. thermophilum (StDapDH) has the positive effects in improving the performance of L-lysine fermentation process by E. coli for the first time
The introducing mode and ammonium availability were investigated, indicating that the co-existence of two pathways and sufficient ammonium availability are good for increasing the final titer of L-lysine with a high carbon yield and productivity in E. coli
Summary
L-lysine, one of the essential amino acids for animals and humans[1], is widely used in feed, food, and pharmaceutical industry, etc. According to the previous reports[9,18], the dehydrogenase pathway acts as an ancillary pathway for the biosynthesis of L-lysine and peptidoglycan in bacteria It is a prerequisite for the increase of carbon flux to meso-DAP19,20. The introducing mode and ammonium availability were investigated, indicating that the co-existence of two pathways and sufficient ammonium availability are good for increasing the final titer of L-lysine with a high carbon yield and productivity in E. coli. These results reported here can serve as a general concept and guidance for breeding high-yielding strains and producing L-lysine in industry
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