TABLE 14.

Summary of studies aimed at growth and fermentation enablement in liquid medium by virtue of heterologous expression of saccharolytic genes

Substrate and hostEnzymes (genes)SubstrateGrowth or fermentationaReference
α-Linked substrates
    K. oxytocaα-Amylase from Bacillus stearothermophilus, pullulanase from Thermoanaerobium brockiiStarch (40 g/liter)Anaerobic fermentation, 15 g of ethanol per liter and 1.4 g of cells per liter171
    S. cerevisiaeGlucoamylase (GA1)Soluble starchCO2 release comparable to control with added amylase302
α-Amylase (amyE), glucoamylase (glaA)Corn starch (10 g/liter)Final optical density of 2.0145
α-Amylase (LKA1)Soluble starch (20 g/liter)Aerobic growth, final optical density >1.5646
Glucoamylase from Rhizopus oryzaeSoluble starch (10 g/liter)Aerobic growth with some ethanol production, final optical density >0.9476
Amylopullulanase (LKA1), pectate lyase (PEL5), polygalacturonase (PEH1), endo-β-1,4-glucanase (END1), cellobiohydrolase (CBH1), exo-β-1,3-d-glucanase (EXG1), cellobiase (BGL1), and endo-β-d-xylanase (XYN4)StarchAerobic growth, cell number > control531
α-Amylase (amyE), glucoamylase (glaA)Soluble starch (100 g/liter)Anaerobic growth, 44 g of ethanol per liter and 8 g of cells per liter57
β-Linked substrates
    K. oxytocaEndoglucanases (celY and celZ)AvicelAnaerobic SSF with added cellulase, ethanol yields up to 22% more than control778
Amorphous celluloseCellulose fermentation without added cellulase, ethanol yields 58-76% theoretical781
    S. cerevisiaeCMCase, β-glucosidase from Aspergillus aculeatusCellobiose (10 g/liter)Aerobic growth, final optical density >1.5476
CMCase, β-glucosidase from Aspergillus aculeatusCellodextrinsAerobic growth, cell number > control476
Amylopullulanase (LKA1), pectate lyase (PEL5), polygalacturonase (PEH1), endo-β-1,4-glucanase (END1), cellobiohydrolase (CBH1), exo-β-1,3-d-glucanase (EXG1), cellobiase (BGL1), and endo-β-d-xylanase (XYN4)CellobioseAerobic growth, cell number > control531
Endo/exoglucanse from Bacillus sp. strain DO4, β-glucosidase genes from Bacillus circulansCellodextrinsGrowth, 2-fold higher cell mass and greater ethanol production compared to control107
Endo/exoglucanse from Bacillus sp. strain DO4, β-glucosidase genes from Bacillus circulansAvicelAnaerobic SSF, showed substantial enzyme production under aerobic and anaerobic conditions106
  • a “Control” refers to a strain not expressing heterologous saccharolytic enzymes.