Abstract
Backgroundl-ornithine is a valuable amino acid with a wide range of applications in the pharmaceutical and food industries. However, the production of l-ornithine by fermentation cannot compete with other methods, because of the low titers produced with this technique. Development of fermentation techniques that result in a high yield of l-ornithine and efficient strategies for improving l-ornithine production are essential.ResultsThis study demonstrates that tween 40, a surfactant promoter of the production of glutamate and arginine, improves l-ornithine production titers in engineered C. glutamicum S9114. The intracellular metabolism under tween 40 triggered fermentation conditions was explored using a quantitative proteomic approach, identifying 48 up-regulated and 132 down-regulated proteins when compared with the control. Numerous proteins were identified as membrane proteins or functional proteins involved in the biosynthesis of the cell wall. Modulation of those genes revealed that the overexpression of CgS9114_09558 and the deletion of CgS9114_13845, CgS9114_02593, and CgS9114_02058 improved the production of l-ornithine in the engineered strain of C. glutamicum Orn8. The final strain with all the exploratory metabolic engineering manipulations produced 25.46 g/L of l-ornithine, and a yield of 0.303 g l-ornithine per g glucose, which was 30.6% higher than that produced by the original strain (19.5 g/L).ConclusionThese results clearly demonstrate the positive effect of tween 40 addition on l-ornithine accumulation. Proteome analysis was performed to examine the impact of tween 40 addition on the physiological changes in C. glutamicum Orn8 and the results showed several promising modulation targets for developing l-ornithine-producing strains.
Highlights
Addition of tween 40 can promote the biosynthesis of l-ornithine by redirecting the carbon flux from the tricarboxylic acid cycle to glutamate accumulation or improving membrane permeability in C. glutamicum
Results after 40 h of C. glutamicum Orn8 fermentation using a shake flask suggests that the production titer was significantly affected by the temporal points of filtration degermed tween 40 addition, and cell growth was reduced when the temporal points of filtration degermed tween 40 addition was less than 6 h (Fig. 1a)
The reduced expression of acetyl-CoA carboxylase, a biotin dependent enzyme encoded by dtsR1 and dtsR2, indicated that the biosynthesis of fatty acids was inhibited by tween 40 addition, which presumably leads to cell wall becomes more permeable by reducing the mycolic acid layer and provide abundant acetyl-CoA for the production of l-ornithine
Summary
The original aim of this study was to find efficient targets for improving l-ornithine production
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