Efficient bioproduction of 5-aminolevulinic acid, a promising biostimulant and nutrient, from renewable bioresources by engineered Corynebacterium glutamicum

Jiuzhou Chen,Xuan Guo,Deming Rao,Wenjuan Zhou,Jibin Sun,Ping Zheng,Yanhe Ma,Yu Wang

doi:10.1186/s13068-020-01685-0

Abstract

Background5-Aminolevulinic acid (5-ALA) is a promising biostimulant, feed nutrient, and photodynamic drug with wide applications in modern agriculture and therapy. Considering the complexity and low yield of chemical synthesis methods, bioproduction of 5-ALA has drawn intensive attention recently. However, the present bioproduction processes use refined glucose as the main carbon source and the production level still needs further enhancement.ResultsTo lay a solid technological foundation for large-scale commercialized bioproduction of 5-ALA, an industrial workhorse Corynebacterium glutamicum was metabolically engineered for high-level 5-ALA biosynthesis from cheap renewable bioresources. After evaluation of 5-ALA synthetases from different sources, the 5-ALA biosynthetic pathway and anaplerotic pathway were rebalanced by regulating intracellular activities of 5-ALA synthetase and phosphoenolpyruvate carboxylase. The engineered biocatalyst produced 5.5 g/L 5-ALA in shake flasks and 16.3 g/L in 5-L bioreactors with a one-step fermentation process from glucose. To lower the cost of feedstock, cheap raw materials were used to replace glucose. Enzymatically hydrolyzed cassava bagasse was proven to be a perfect alternative to refined sugars since the final 5-ALA titer further increased to 18.5 g/L. Use of corn starch hydrolysate resulted in a similar 5-ALA production level (16.0 g/L) with glucose, whereas use of beet molasses caused seriously inhibition. The results obtained here represent a new record of 5-ALA bioproduction. It is estimated that replacing glucose with cassava bagasse will reduce the carbon source cost by 90.1%.ConclusionsThe high-level biosynthesis of 5-ALA from cheap bioresources will brighten the prospects for industrialization of this sustainable and environment-friendly process. The strategy for balancing metabolic flux developed in this study can also be used for improving the bioproduction of other value-added chemicals.

Highlights

ALA synthetase (ALAS) screening for 5‐ALA production in C. glutamicum Since ALAS is an essential enzyme for 5-Aminolevulinic acid (5-ALA) production via C4 pathway and it is absent from C. glutamicum, introduction of a heterogeneous ALAS is required (Fig. 1)
In this study, we showed that 5-ALA production could be greatly enhanced by accurately regulating the expression of key enzymes involved in 5-ALA biosynthetic pathway and anaplerotic pathway in C. glutamicum
The best producer strain CA1P4 produced the highest 5-ALA titer up to 18.5 g/L using cheap renewable bioresources including cassava bagasse in 39 h fermentation, which is the highest titer for 5-ALA bioproduction reported to date

Summary

Results

To lay a solid technological foundation for large-scale commercialized bioproduction of 5-ALA, an industrial workhorse Corynebacterium glutamicum was metabolically engineered for high-level 5-ALA biosynthesis from cheap renewable bioresources. The engineered biocatalyst produced 5.5 g/L 5-ALA in shake flasks and 16.3 g/L in 5-L bioreactors with a one-step fermentation process from glucose. To lower the cost of feedstock, cheap raw materials were used to replace glucose. Hydrolyzed cassava bagasse was proven to be a perfect alternative to refined sugars since the final 5-ALA titer further increased to 18.5 g/L. Use of corn starch hydrolysate resulted in a similar 5-ALA production level (16.0 g/L) with glucose, whereas use of beet molasses caused seriously inhibition. The results obtained here represent a new record of 5-ALA bioproduction. It is estimated that replacing glucose with cassava bagasse will reduce the carbon source cost by 90.1%

Conclusions

Results and discussion

Methods