Table 1.

Summary of the metabolic engineering optimization strategies used for the production of lycopene in E. coli.

Major Methods	Optimization Strategies	Yield/Titer	Culture Conditions	References
Overexpression of rate-limiting enzymes	Comparison of crtEBI genes from different strains	59 mg/L	-	[15]
	Knockout of zwf; overexpression of idi, dxs and ispD, ispF	7.55 mg/g DCW	Shake-flask fermentation	[28]
	Overexpression of crtE, crtB, crtI, ipi, dxs	5.2 mg/g DCW	Shake-flask fermentation	[29]
	Overexpression of dxs, dxr	22 mg/L	Shake-flask fermentation	[31]
	Overexpression of dxs	1.33 mg/g DCW	Shake-flask fermentation	[32]
	The co-expression of appY, crl, and rpoS with dxs	4.7 mg/g DCW	-	[29]
Directed evolution	Directed evolution of GGPP synthase	45 mg/g DCW	Shake-flask fermentation	[33]
	Directed co-evolution of dxs, dxr and idi	0.65 mg/L	-	[34]
Whole pathway engineering	Expression of the MVA pathway	4.28 mg/L	Shake-flask fermentation	[35]
	Type 2 IDI; heterologous MVA pathway	198 mg/g DCW	Shake-flask fermentation	[36]
	Heterologous expression of the MVA pathway	-	Shake-flask fermentation	[37]
Removal of competing pathways	ΔgdhA, ΔaceE, ΔytjC (gpmB), ΔfdhF	18 mg/g DCW	Batch shake-flask cultivations	[38]
Pathway balancing	Combination of gene knockout and overexpression	2.5 mg/g DCW	-	[20]
	Genome-wide stoichiometric flux balance analysis; genes knockouts	6.6 mg/g DCW	Shake-flask fermentation	[39]
	Gene knockout (Δhnr, ΔyliE)	-	Shake-flask fermentation	[40]
Regulatory engineering	Ntr regulon, stimulated by excess glycolytic flux through sensing of ACP	0.16 mg/L/h	Shake-flask fermentation	[41]
	Engineering of the cAMP receptor protein (CRP)	18.49 mg/g DCW	Batch fermentation	[42]
Optimization of carbon sources	Auxiliary carbon source optimization	1050 mg/L	Baffled flask fermentation	[12]
	Supplementing auxiliary carbon sources	40 mg/L/h	Fed-batch culture	[43]
	Fermentation with fatty acids or waste cooking oils	94 mg/g DCW	Fed-batch fermentation	[44]
Optimization of fermentation	High cell density fermentation	220 mg/L	Batch fermentation	[45]
	Different types of plasmid expression; optimization of fermentation conditions	67 mg/g DCW	Shake-flask fermentation	[46]
Targeted engineering	Targeted engineering; targeted proteomic and intermediate analysis	1.23 g/L	Fed-batch fermentation	[47]
	Two-dimensional search for gene targets	16 mg/g DCW	Shake-flask fermentation	[48]
Cofactor engineering	Modulating supply of NADPH and ATP; overexpression of dxs, idi and the crt gene operon	50.6 mg/g DCW	Fed-batch fermentation	[27]
Membrane engineering	Membrane engineering; overexpression of plsb, plsc and dgka	36.4 mg/g DCW	Shake-flask fermentation	[49]
Genome engineering	Synthesis genes were integrated into chromosome	33.43 mg/g DCW	Shake-flask fermentation	[50]
	Large-scale programming used to optimize the MEP pathway	9 mg/g DCW	-	[51]
	A new combinatorial multi-gene pathway assembly scheme	448 mg/g DCW	-	[52]