Table 1.
Metabolic engineering for overproduction of RF by gene manipulation
| Organism | GOIa and Manipulationb | Riboflavin titersc | Improvement | References |
|---|---|---|---|---|
| Overexpression of the RF synthesis pathway | ||||
| B. subtilis | ribA + | c−1 | 25% | [40] |
| B. subtilis | rib operon + | 0.4–0.7 | Tenfold | [52] |
| B. subtilis | rib operon + | 4.3 | 27% | [87] |
| A. gossypii | RIB genes + | 0.327 | 3.1-fold | [53] |
| E. coli | ribABDEC + | 0.229 | – | [54] |
| C. ammoniagenes | rib genes + | 15.3 | 16-fold | [88] |
| C. famata | RIB1 +, RIB7 + | 16.4 | 62-fold | [30] |
| E. ashbyi | RIB1 +, RIB3 + | 0.331 | 1.44-fold | [89] |
| L. lactis | ribGBAH | 0.024 | – | [90] |
| Overexpression of the purine biosynthesis pathway | ||||
| B. subtilis | purF + | ~ 5.1 | 31% | [91] |
| B. subtilis | ΔpurR, purF* | 0.827 | Threefold | [92] |
| A. gossypii | prs + , AGR371C +, AGL080C + | 0.05 | 80% | [93] |
| A. gossypii | AER117W+ | ~ 0.12c−2 | 40% | [94] |
| A. gossypii | ADE4 + , SHM+ | 24.28 mg/gc−3 | 12-fold | [95] |
| A. gossypii | AgADE4*+ | 0.228 | Tenfold | [96] |
| A. gossypii | ΔAgURA3 | 7.5 mg/gc−4 | 6.5 | [97] |
| E. coli | (ndk, gmk, purA, purF and prs) + | 0.388 | 72% | [98] |
| L. fermentum | ΔfolE | 3.49 mg/L | 50% | [99] |
| Optimization of the central carbon metabolism | ||||
| B. subtilis | zwf+ | ~ 0.8 | 25% | [100] |
| B. subtilis | zwf + , gnd+ | 15.7 | 39% | [101] |
| B. subtilis | fbp + , pckA + , gapB+ | 13.36 | 27.8% | [102] |
| B. subtilis | ΔccpN | ~ 13 | ~ 28% | [103] |
| E. coli | Δpgi, Δedd, Δeda | 0.56 | – | [54] |
| Enhanced synthesis of glycine | ||||
| A. gossypii | GLY1+ | ~ 16 mg/gc−4 | Ninefold | [104] |
| A. gossypii | ΔSHM2 | 9.6 mg/gc−4 | Tenfold | [105] |
| A. gossypii | AGX1+ | ~ 0.15 | 30% | [106] |
| Other strategies | ||||
| B. subtilis | ΔcydC | 12.3 | 38% | [107] |
| B. subtilis | HSPs+ | ~ 0.3–0.35 | 23–66% | [108] |
aGOI represents the gene of interest. ribA, DHPB synthase; RIB1, GTP cyclohydrolase II; RIB7, RF synthase; RIB3, DHPB synthase; purF, PRPP amidotransferase; purR, purine repressor PurR; AGR371C and AGL080C, PRPP synthetases; prs, PRPP synthetase; purF, PRPP amidotransferase; AER117W, IMP dehydrogenase; ADE4, PRPP amidotransferase; SHM1 and SHM2, serine hydroxymethyltransferase; AgURA3, orotidine-5′-phosphate decarboxylase; zwf, glucose-6-phosphate dehydrogenase; gnd, 6-phosphogluconate dehydrogenase; fbp, fructose-1,6-bisphosphatase; pckA, phosphoenolpyruvate carboxykinase; gapB, glyceraldehyde-3-phosphate dehydrogenase; ccpN, gluconeogenic repressor CcpN; pgi, glucose-6-phosphate isomerase; edd, phosphogluconate dehydratase; eda, multifunctional 2-keto-3-deoxygluconate 6-phosphate aldolase and 2-keto-4-hydroxyglutarate aldolase and oxaloacetate decarboxylase; GLY1, threonine aldolase; SHM2, serine hydroxymethyltransferase; AGX1, alanine-glyoxylate aminotransferase; cydC, cytochrome bd oxidase; HSPs, heat shock proteins; folE, GTP cyclohydrolase I
b“+”indicates gene over-expression; “−” indicates gene downregulation; “Δ” indicates gene knockout; “*” indicates gene mutation
cThe maximum RF titer of the engineered strains. Unit: g/L unless otherwise specified; c−1, Strain VB2XL1 produced up to 25% more RF as compared to its parent strain RB50::[pRF69]n::[pRF93]m Ade; c−2, total (intracellular +extracellular) RF concentration; c−3, mg/g of biomass; c−4, mg/g mycelium