Table 1 Selected examples of four major target categories where genetic engineering strategies were applied to improve product formation by microorganisms
From: Genetic improvement of microorganisms for applications in biorefineries
Organism | Product | Main substrate | Yield* | Productivity | Concentration | Outcomes | Main genetic modifications | Reference |
|---|---|---|---|---|---|---|---|---|
Driving carbon flux towards the desired pathway | ||||||||
E. coli SY4 | Ethanol | Glycerol | 0.42 g g-1 | 0.15 g L-1 h-1 | 7.8 g L -1 | Yield improved 69 fold. Engineered strains efficiently utilized glycerol in a minimal medium without rich supplements | Deletion of genes to minimize the synthesis of by-products | [7] |
E. coli LA02Δdld | Lactic acid | Glycerol | 0.80 g g-1 | 1.25 g g-1 h-1 | 32 g L -1 | Low-value glycerol streams to a higher- value product like D-lactate. Yield improved seven fold | Overexpression of pathways involved in the conversion of glycerol to lactic acid and blocking those leading to the synthesis of competing by-products | [8] |
E. coli | Acetate | Glucose | 0.456 g g-1 | 1.38 g g-1 h-1 | 53 g L -1 | Reduction of the fermentation by products concentration by 1, 25 (succinate) to 33 fold (lactate). Yield improved over seven fold | Deletion of genes involved in the succinate formation as fermentation product | [9] |
Y. lipolytica | Succinic acid | Glycerol | 0.45 g g-1 | n.d | 45 g L -1 | Succinic acid production yield increased over 20 fold | Deletion in the gene coding one of succinate dehydrogenase subunits | [10] |
Y-3314 | ||||||||
Mannheimia succiniciproducens | Succinic Acid | Glucose | 0.76 g g-1 | 1.8 g g-1 h-1 | 52.4 g L -1 | Nearly complete elimination of fermentation by-products, (acetic, formic, and lactic acids) and carbon recovery increased to 58% to 77% by fed-batch culture | Disruption of genes responsible for by product formation (ldhA, pflB, pta, and ackA ) | [11] |
Increasing of tolerance to toxic compounds | ||||||||
C. acetobutylicum | Butanol | Glucose | n.d. | n.d. | Increased tolerance and extended metabolism response to butanol stress. | Overexpression of spo0A, responsible for the transcription of solvent formation genes | [12] | |
C. acetobutylicum | Butanol | Glucose | 70.8% | n.d. | 13.6 g L -1 | Reduction of acetone production from 2,83 g L-1 to 0,21 g L-1 and enhanced butanol yield from 57% to 70.8 | Disruption of the acetoacetate decarboxylase gene (adc) avoiding acetone production and optimization of medium | [13] |
S. cerevisiae | Ethanol | Glucose plus HMF (inhibitor) | 0.43 g g-1 | 0.61 g g-1 h-1 | n.d | Four times higher specific uptake rate of HMF and 20% higher specific Ethanol productivity | Overexpression of alcohol dehydrogenases ADH6 or ADH1-mutated | [14] |
S. cerevisiae | Ethanol | Spruce hydrolystae | n.d | 0.39 g g-1 h-1 | n.d | HMF conversion rate and ethanol productivity for the engineered strains four to five times and 25% higher than for the control strain. | Overexpression of alcohol dehydrogenases ADH6 or ADH1-mutated | [14] |
E. coli XW068(pLOI4319) | Lactate | Xylose plus HMF | 85% of the theoretical maximum | n.d. | n.d | Furfural tolerance increased by 50%. Minimal growth and lactate production occurred after 120 h for the control strain | Overexpression of NADH-dependent propanediol oxidoreductase (FucO) | [15] |
Increasing substrate uptake range | ||||||||
E. coli | Ethanol | Xylose | 0.48 g g-1 | 2.00 g g-1 h-1 | 43 g L -1 | Rapid co-fermentation due to reduced repression of xylose metabolism by glucose, and 60% less time required for fermentation of 5-sugars mix to ethanol. | Deletion of methylglyoxal synthase gene (mgsA), involved in sugar metabolism | [16] |
Lactobacillus plantarum | Lactic Acid | Corn starch | 0.89 g g-1 | 4.51 g g-1 h-1 | 86 g L -1 | First direct and efficient fermentation of optically pure D- lactic acid from raw corn starch reported | Deletion of L-lactate dehydrogenase gene (ldhL1) and expression of Streptococcus bovis 148 α-amylase (AmyA) | [17] |
S. cerevisiae | Ethanol | Xylose | 0.43 g g-1 | 0.02 g g-1 h-1 | 7.3 g L -1 | Higher ethanol yields than XR/XDH carrying strains | Overexpression of Piromyces sp xylose isomerase (XI) | [18] |
S. cerevisiae | Ethanol | Xylose | 0.33 g g-1 | 0.04 g g-1 h-1 | 13.3 g L -1 | Higher specific ethanol productivity and final ethanol concentration than XI carrying strains | Overexpression of xylose reductase (XR) and xylitol dehydrogenase (XDH) enzymes from Scheffersomyces stipitis | [19] |
E. coli | Butanol | Glucose | 6.1% | 0.02 g g-1 h-1 | 1.2 g L -1 | Anaerobic production of butanol by a microorganism expressing genes from a strict aerobic organism | Expression of C. acetobutylicum butanol pathway sinthetic genes in E. coli | [20] |
Generation of new products | ||||||||
E. coli | Fatty acid ethyl esters (FAEEs) | Glucose | 7% | n.d. | 30.7 g L -1 | Tailored fatty ester (biodiesel) production | Heterologous expression of a “FAEE pathway” engineered in E. coli | [21] |
S. cerevisiae | Butanol | Galactose | n.d | n.d | 2.5 mg L -1 | First demonstration of n-butanol production in S. cerevisiae | N-butanol biosynthetic pathway engineered in S. cerevisiae | [22] |
E. coli K12 | 1,3-propandiol | Glycerol | 90.2% | 2.61 g g-1 h-1 | 104.4 g L -1 | Substantially high yield and productivity efficiency of 1,3-PD with glycerol as the sole source of carbon | Heterologous overexpression of genes from natural producers of 1,3-PDO | [23]. |