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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]
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].
  1. *expressed in g product per g substrate or% of maximum theoretical; n.d. not determined; n.c. not calculated.