Recent Advances in Second Generation Ethanol Production by Thermophilic Bacteria
Abstract
:1. Introduction
2. Ethanol Production from Biomass
2.1. Difference between First and Second Generation Ethanol Production
2.2. Comparison between Mesophilic and Thermophilic Microbes Producing Ethanol
- Minimal by-product formation;
- High productivity (>1 g/L/h);
- GRAS-status;
- Broad tolerance to environmental conditions;
- High ethanol tolerance;
- Broad substrate spectra;
- No “glucose effect”;
- High cellulolytic activity;
- Tolerant to inhibitory compounds;
- Tolerate high solid and substrate loadings;
- Simple nutritional needs;
- Low biomass production;
- Ease of genetic manipulation.
- >90% of theoretical yield;
- High ethanol titers (>5% (v/v));
- Minimum number of process steps;
- Minimal process cooling;
- Recyclable cells;
- Co-fermentation of substrates;
- Limited or no pretreatment;
- Limited or no pretreatment.
3. Thermophilic Ethanol Producers
Microorganism | Selected substrate spectra | Polymer degrading ability | Ethanol tolerance | Inhibitor tolerance | Fermentation products | Max ethanol yields (mol/mol sugar) | Topt (°C) | References |
---|---|---|---|---|---|---|---|---|
Caloramator boliviensis | g, gal, man, x, a, cel, suc | X | ND | ND | E, A, L, P, H | 1.53 (x) | 60 | [28,43] |
Clostridium thermocellum | g *, cel | C | 4%–5% | ND | E, A, L, F, H | 1.53 (g) | 60 | [44,45,46,47] |
Clostridium AK1 | g, gal, man, x, suc | S, X, P | ND | ND | E, A, H | 1.50 (g), 0.85 (x) | 50 | [48] |
Thermoanaerobacterium saccharolyticum | g, gal, man, x, a, cel, suc | S, X | NR | NR | E, A, L, H | 1.18 (x) | 60 | [40,49] |
Thermoanaerobacterium AK17 | g, gal, man, x, a, suc | P | 3.2% | 4 g/L FF 6 g/L HMF | E, A, H | 1.50 (g), 1.33 (x) | 60 | [42,50] |
Thermoanaerobacter ethanolicus | g, gal, man, x, cel, suc | S, X | 0.5%–5.0% | ND | E, A, L, H | 1.90 (g), 1,64 (x) | 70 | [16,51,52] |
Thermoanaerobacter pseudoethanolicus | g, cel, suc | S, X, P | 4% | ND | E, A, L, H | 1.88 (g) | 67–69 | [53,54] |
Thermoanaerobacter mathranii | g, man, x, a, cel, suc | S, X, P, I | 5% | 2% ArC | E, A, L, H | 1.37 (x) | 70 | [17,55] |
Thermoanaerobacter pentosaceus | g, gal, man, x, a, cel, suc | S, X, P, I | 0.5% | 3.4 g/L FF 3.4 g/L HMF | E, A, L, H | 1.68 (x) | 70 | [56,57] |
Thermoanaerobacter AK5 | g, gal, man, x, cel | S | ND | ND | E, A, H | 1.70 (g), 1.35 (x) | 65 | [58] |
Thermoanaerobacter J1 | g, gal, man, x, a, cel | S | ND | ND | E, A, H | 1.70 (g), 1.25 (x) | 65 | [18] |
4. Physiology of Thermophilic Anaerobic Bacteria
4.1. Central Metabolism of Sugars to Various end Products
4.2. Effect of Various Factors for Ethanol Production
4.2.1. Partial Pressure of Hydrogen
4.2.2. Substrate Loadings
4.2.3. Ethanol Tolerance
4.2.4. Other Culture Parameters
5. Production of Ethanol from Lignocellulose
Organisms | Substrate | Fermentation mode | Substrate (g/L) | Pre-treatment | Ethanol yields (mM/g) | T (°C) | References |
---|---|---|---|---|---|---|---|
Clostridium thermocellum | Avicel | Batch | 2.5 | A | 5.00 | 60 | [93] |
Clostridium thermocellum | Avicel | Con | 5.0 | A | 5.48 | 60 | [94] |
Clostridium thermocellum | Whatman paper | Batch | 8.0 | None | 7.20–8.00 | 60 | [95] |
Clostridium thermocellum | Paddy straw | Batch | 8.0 | None | 6.10–8.00 | 60 | [95] |
Clostridium thermocellum | Sorghum stover | Batch | 8.0 | None | 4.80–8.10 | 60 | [95] |
C. thermocellum and C. thermolacticum | Microcrystal cellulose | Batch | 10.0 | None | 9.1 | 57 | [96] |
Clostridium AK1 | Hemp | Batch | 5.0 | A/Alk | 3.5 | 50 | [48] |
Thermoanaerobacter pentosaceus | Rapeseed straw | Con | 50 | Alk | 1.40 | 70 | [57] |
Thermoanaerobacter mathranii | Wheat straw | Batch | 6.7 | WO/E | 2.61 | 70 | [87] |
Thermoanaerobacter mathranii | What straw | Batch | 60.0 | WO/E | 5.30 | 70 | [97] |
Thermoanaerobacter ethanolicus | Beet molasses | Batch | 30.0 | None | 4.81 | 65 | [98] |
Thermoanaerobacter BG1L1 | Corn stover | Batch | 25.0–150.0 | WO/E | 8.50–9.20 | 70 | [60] |
Thermoanaerobacter BG1L1 | Wheat straw | Batch | 30.0–120.0 | WO/E | 8.50–9.20 | 70 | [92] |
Thermoanaerobacter BG1L1 | Corn stover | Con | 25.0–150.0 | WO/E | 8.50–9.20 | 70 | [60] |
T. ethanolicus | Wood HL | Batch | 8.0 | E | 3.30–4.50 | 70 | [89] |
Thermoanaerobacter AK5 | Whatman paper | Batch | 2.25 | E | 7.7 | 65 | [58] |
Thermoanaerobacter AK5 | Grass | Batch | 4.5 | A/E | 4.31 | 65 | [58] |
Thermoanaerobacter J1 | Whatman paper | Batch | 4.5 | E | 7.5 | 65 | [18] |
Thermoanaerobacter J1 | Hemp | Batch | 4.5 | A/E | 4.3 | 65 | [18] |
T. saccharoylticum | Xylan | Batch | 10.0 | WO | 6.30 | 60 | [86] |
Thermoanaerobacterium AK17 | Cellulose | Batch | 2.5 | E | 8.6 | 60 | [42] |
Thermoanaerobacterium AK17 | Grass | Batch | 2.5 | A/Alk/E | 5.5 | 60 | [42] |
6. Evolutionary Adaptation and Genetic Engineering of Thermophiles
6.1. Evolutionary Adaptation
6.2. Genetic Engineering
Strain | Genotype | Substrate | Concentration (g/L) | Mode | Ethanol yields (mol/mol) | References |
---|---|---|---|---|---|---|
C. thermocellum | ΔpyrF, Δpta::gapDHp-cat | Cellobiose | 5.0 | Batch | 0.59 | [111] |
C. thermocellum | ΔpyrF, Δpta::gapDHp-cat | Avicel | 5.0 | Batch | 0.71 | [111] |
C. thermocellum adhE*(EA) Δldh | Δhpt, Δldh | Cellobiose | 5.0 | Batch | 0.37 | [112] |
C. thermocellum | Δhpt, Δldh, Δpta (evolved) | Avicel | 19.5 | Batch | 1.08 | [112] |
C. thermocellum/T. saccharolyticum | Δhpt, Δldh, Δpta (evolved) and Δpta, Δack, Δldh | Avicel | 19.5 | Batch | 1.26 | [112] |
T. saccharolyticum TD1 | Δldh | Xylolse | 5.0 | Batch | 0.98 | [112] |
T. saccharolyticum ALK2 | Δpta, Δack, Δldh | Cellobiose | 70.0 | Con | ND | [49] |
T. saccharolyticium HK07 | Δldh , Δhfs | Cellobiose | 1.8 | Batch | 0.86 | [110] |
T. saccharolyticium M0355 | Δldh , Δack Δpta | Cellobiose | 50.0 | Batch | 1.73 | [106] |
T. saccharolyticum M1051 | Δldh , Δack Δpta, ureABCDEFG | Cellobiose | 27.5 | Batch | 1.73 | [110] |
G. thermoglucosidasius TM242 | Δldh-, pdh up, pflB- | Glucose | 34.0 | Batch | 1.73 | [70] |
G. thermoglucosidasius TM242 | Δldh-, pdh up, ΔpflB- | Glucose | 34.0 | Batch | 1.84 | [70] |
G. thermoglucosidasius TM242 | Δldh-, Δpdh up, ΔpflB- | Xylose | 29.0 | Batch | 1.37 | [70] |
T. mathranii BG1L1 | Δldh | Wheat straw | 30–120 | Con | 1.53–1.67 | [92] |
T. mathranii BG1G1 | Δldh, GldA | Glucose + glycerol | 5.0 | Batch | 1.68 | [55] |
T. mathranii BG1G1 | Δldh, GldA | Xylose + glycerol | 5.0 | Batch | 1.57 | [55] |
T. mathranii BG1G1 | Δldh, GldA | Xylose + glycerol | 12.8 and 7.2 | Con | 1.53 | [55] |
7. Process Technology for Thermophilic Bioethanol Production
- 1)
- Physical and chemical pretreatment of biomass;
- 2A)
- Hydrolases production (cellulases, hemicellulases, etc.);
- 2B)
- accharification (enzymatic hydrolysis of polymers to hexoses and pentoses);
- 3)
- Fermentation (of both pentoses and hexoses);
- 4)
- Product recovery.
7.1. Process Steps for the Conversion of Lignocellulosic Biomass to Ethanol
7.1.1. Pretreatment of Biomass
7.1.2. Enzymatic Hydrolysis and Saccharification
7.1.3. Fermentation
7.1.4. Product Recovery
7.2. Integrated Processes for Ethanol Production from Lignocellulose
7.2.1. Separate Hydrolysis and Fermentation
7.2.2. Simultaneous Saccharification and Fermentation and Simultaneous Saccharification and Co-Fermentation
7.2.3. Consolidated Bioprocessing
8. Conclusions
Acknowledgments
Conflicts of Interest
References
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Scully, S.M.; Orlygsson, J. Recent Advances in Second Generation Ethanol Production by Thermophilic Bacteria. Energies 2015, 8, 1-30. https://doi.org/10.3390/en8010001
Scully SM, Orlygsson J. Recent Advances in Second Generation Ethanol Production by Thermophilic Bacteria. Energies. 2015; 8(1):1-30. https://doi.org/10.3390/en8010001
Chicago/Turabian StyleScully, Sean Michael, and Johann Orlygsson. 2015. "Recent Advances in Second Generation Ethanol Production by Thermophilic Bacteria" Energies 8, no. 1: 1-30. https://doi.org/10.3390/en8010001
APA StyleScully, S. M., & Orlygsson, J. (2015). Recent Advances in Second Generation Ethanol Production by Thermophilic Bacteria. Energies, 8(1), 1-30. https://doi.org/10.3390/en8010001