Abstract
Background
The non-proteinogenic aromatic amino acid, p-amino-l-phenylalanine (l-PAPA) is a high-value product with a broad field of applications. In nature, l-PAPA occurs as an intermediate of the chloramphenicol biosynthesis pathway in Streptomyces venezuelae. Here we demonstrate that the model organism Escherichia coli can be transformed with metabolic grafting approaches to result in an improved l-PAPA producing strain.
Results
Escherichia coli K-12 cells were genetically engineered for the production of l-PAPA from glycerol as main carbon source. To do so, genes for a 4-amino-4-deoxychorismate synthase (pabAB from Corynebacterium glutamicum), and genes encoding a 4-amino-4-deoxychorismate mutase and a 4-amino-4-deoxyprephenate dehydrogenase (papB and papC, both from Streptomyces venezuelae) were cloned and expressed in E. coli W3110 (lab strain LJ110). In shake flask cultures with minimal medium this led to the formation of ca. 43 ± 2 mg l−1 of l-PAPA from 5 g l−1 glycerol. By expression of additional chromosomal copies of the tktA and glpX genes, and of plasmid-borne aroFBL genes in a tyrR deletion strain, an improved l-PAPA producer was obtained which gave a titer of 5.47 ± 0.4 g l−1 l-PAPA from 33.3 g l−1 glycerol (0.16 g l-PAPA/g of glycerol) in fed-batch cultivation (shake flasks). Finally, in a fed-batch fermenter cultivation, a titer of 16.7 g l−1 l-PAPA was obtained which is the highest so far reported value for this non-proteinogenic amino acid.
Conclusion
Here we show that E. coli is a suitable chassis strain for l-PAPA production. Modifying the flux to the product and improved supply of precursor, by additional gene copies of glpX, tkt and aroFBL together with the deletion of the tyrR gene, increased the yield and titer.
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