Fig. 5
Dynamic metabolic regulation for improved serine production in E. coli using the glycine-OFF riboswitch glyOFF6. a Schematic representation of the metabolic pathways involved in serine production from glucose in recombinant E. coli. The expression of glyA, encoding serine hydroxymethyltransferase, was dynamically regulated under the synthetic glycine-OFF riboswitch glyOFF6 in plasmid pUC18, co-expressed with pPK10 to produce serine in E. coli. The genes sdaA, encoding L-serine deaminase I; sdaB, encoding L-serine deaminase II; and tdcG, encoding L-serine deaminase III were deleted, serAΔ197, (encoding a truncated 3-phosphoglycerate dehydrogenase gene from C. glutamicum), serC (encoding phosphoserine aminotransferase), serB (encoding phosphoserine phosphatase) and pgk (encoding phosphoglycerate kinase) were upregulated by overexpression using the plasmid pPK10. GLU, glucose; PGA, 3-phosphoglycerate; PEP, phosphoenolpyruvate; ISO, isocitrate; AKG, α-ketoglutaric acid; FUM, fumaric acid; OAA, oxaloacetic acid; TCA cycle: tricarboxylic acid cycle; PGA, 3-phosphoglycerate; PEP, phosphoenolpyruvate; PYR, pyruvate; Ac-CoA, acetyl coenzyme A; PAP, 3-phosphopyruvate; S3P, 3-phosphoserine; MTPG, methylene-tetrahydropteroyl polyglutamate; AMHDP, s-amino-methyldihydrolipoyl protein; GLY, glycine; SER, serine; Amp: ampicillin, Cr: chloramphenicol resistance gene; ori, replicon; glycine-OFF riboswitch glyOFF6 in the solid line box; b OD600, glucose consumption, and serine production of engineered strain E4GS and control strain E4GD in M9Y medium under aerobic conditions with an initial OD600 of 0.05. (Black solid circle: E4GD OD600; Black solid square: E4GD OD600; Blue falling triangle: E4GD glucose consumption; Blue positive triangle: E4GS glucose consumption; Red diagonal triangle: E4GD serine production; Red rhombus: E4GS serine production) Error bars represent the standard deviations of triplicate samples