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Wang D, Ju X, Zhou D, Wei G. Efficient production of pullulan using rice hull hydrolysate by adaptive laboratory evolution of Aureobasidium pullulans. BIORESOURCE TECHNOLOGY 2014; 164:12-9. [PMID: 24835913 DOI: 10.1016/j.biortech.2014.04.036] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/08/2014] [Revised: 04/09/2014] [Accepted: 04/10/2014] [Indexed: 05/09/2023]
Abstract
Pullulan production by Aureobasidium pullulans CCTCC M 2012259 using rice hull hydrolysate as the carbon source was conducted. The acetic acid in the hydrolysate was demonstrated to exert a negative effect on pullulan biosynthesis. Instead of employing expensive methods to remove acetic acid from the hydrolysate, a mutant A. pullulans ARH-1 was isolated following 20 cycles of adaptive laboratory evolution of the parental strain on medium containing acetic acid. The maximum pullulan production achieved by the adapted mutant at 48 h using the hydrolysate of untreated rice hull was 22.2 g L(-1), while that obtained by the parental strain at 60 h was 15.6 g L(-1). The assay of key enzymes associated with pullulan biosynthesis revealed that acetic acid inhibited enzyme activity rather than suppressing enzyme synthesis. These results demonstrated that adaptive evolution highly improved the efficiency of pullulan production by A. pullulans using the hydrolysate of untreated rice hull.
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Affiliation(s)
- Dahui Wang
- School of Biology and Basic Medical Sciences, Soochow University, Suzhou 215123, PR China
| | - Xiaomin Ju
- School of Biology and Basic Medical Sciences, Soochow University, Suzhou 215123, PR China
| | - Donghai Zhou
- School of Biology and Basic Medical Sciences, Soochow University, Suzhou 215123, PR China
| | - Gongyuan Wei
- School of Biology and Basic Medical Sciences, Soochow University, Suzhou 215123, PR China; State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing University of Technology, Nanjing 210009, PR China.
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152
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Doğan A, Demirci S, Aytekin AÖ, Şahin F. Improvements of tolerance to stress conditions by genetic engineering in Saccharomyces cerevisiae during ethanol production. Appl Biochem Biotechnol 2014; 174:28-42. [PMID: 24908051 DOI: 10.1007/s12010-014-1006-z] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2013] [Accepted: 05/29/2014] [Indexed: 02/07/2023]
Abstract
Saccharomyces cerevisiae, industrial yeast isolate, has been of great interest in recent years for fuel ethanol production. The ethanol yield and productivity depend on many inhibitory factors during the fermentation process such as temperature, ethanol, compounds released as the result of pretreatment procedures, and osmotic stress. An ideal strain should be able to grow under different stress conditions occurred at different fermentation steps. Development of tolerant yeast strains can be achieved by reprogramming pathways supporting the ethanol metabolism by regulating the energy balance and detoxicification processes. Complex gene interactions should be solved for an in-depth comprehension of the yeast stress tolerance mechanism. Genetic engineering as a powerful biotechnological tool is required to design new strategies for increasing the ethanol fermentation performance. Upregulation of stress tolerance genes by recombinant DNA technology can be a useful approach to overcome inhibitory situations. This review presents the application of several genetic engineering strategies to increase ethanol yield under different stress conditions including inhibitor tolerance, ethanol tolerance, thermotolerance, and osmotolerance.
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Affiliation(s)
- Ayşegül Doğan
- Department of Genetics and BioEngineering, Faculty of Engineering and Architecture, Yeditepe University, 26 Ağustos Campus, Kayisdagi cad., Kayisdagi, TR-34755, Istanbul, Turkey,
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153
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Laccase applications in biofuels production: current status and future prospects. Appl Microbiol Biotechnol 2014; 98:6525-42. [DOI: 10.1007/s00253-014-5810-8] [Citation(s) in RCA: 112] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2014] [Revised: 04/30/2014] [Accepted: 05/01/2014] [Indexed: 11/27/2022]
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154
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Ran H, Zhang J, Gao Q, Lin Z, Bao J. Analysis of biodegradation performance of furfural and 5-hydroxymethylfurfural by Amorphotheca resinae ZN1. BIOTECHNOLOGY FOR BIOFUELS 2014; 7:51. [PMID: 24708699 PMCID: PMC4101820 DOI: 10.1186/1754-6834-7-51] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2013] [Accepted: 03/07/2014] [Indexed: 05/03/2023]
Abstract
BACKGROUND Furfural and 5-hydroxymethylfurfural (HMF) are the degradation products of lignocellulose during pretreatment operations and significantly inhibit the consequent enzymatic hydrolysis and fermentation processes. The biodetoxification fungus Amorphotheca resinae ZN1 had demonstrated its excellent capacity on degrading lignocellulose derived inhibitors and helped the fermentation processes to achieve high yield of ethanol and biochemicals. Analysis of the biological degradation performance of furfural and HMF by A. resinae ZN1 will provide essential information for their fast and complete removal from the pretreated lignocellulose materials and facilitate the consequent ethanol fermentation. RESULTS The degradation performance of furfural and HMF by A. resinae ZN1 was investigated by capturing intermediate metabolic products at various culture conditions. A. resinae ZN1 converts furfural/HMF into furfuryl/HMF alcohols and furoic/HMF acids simultaneously at aerobic condition, and only the corresponding furfuryl/HMF alcohols are obtained at anaerobic condition. The existence of glucose accelerates the degradation rate of furfural and HMF by A. resinae ZN1 and the cell mass growth rate aerobically. Remarkably, glucose is not consumed before furfural or HMF is degraded to a low threshold concentration. The finding suggests that furfural or HMF has a substrate priority of utilization by A. resinae ZN1 than glucose. This property may help the detoxification of furfural and HMF to be operated without consuming glucose. CONCLUSIONS The biological degradation performance of furfural and HMF by A. resinae ZN1 was investigated experimentally. Oxygen supply is important on the complete biodegradation of furfural and HMF by A. resinae ZN1. Furfural or HMF has the priority of substrate utilization than glucose by A. resinae ZN1. This study provided important information for detoxification enhancement and strain modification.
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Affiliation(s)
- Hong Ran
- State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, China
| | - Jian Zhang
- State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, China
| | - Qiuqiang Gao
- State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, China
| | - Zhanglin Lin
- Department of Chemical Engineering, Tsinghua University, Beijing 100084, China
| | - Jie Bao
- State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, China
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155
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Yu X, Zeng J, Zheng Y, Chen S. Effect of lignocellulose degradation products on microbial biomass and lipid production by the oleaginous yeast Cryptococcus curvatus. Process Biochem 2014. [DOI: 10.1016/j.procbio.2013.10.016] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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156
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Nikel PI, de Lorenzo V. Robustness of Pseudomonas putida KT2440 as a host for ethanol biosynthesis. N Biotechnol 2014; 31:562-71. [PMID: 24572656 DOI: 10.1016/j.nbt.2014.02.006] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2014] [Revised: 02/10/2014] [Accepted: 02/15/2014] [Indexed: 12/01/2022]
Abstract
Expansion of the burgeoning biofuels agenda involves not only the design of suitable genetic and metabolic devices but also their deployment into suitable hosts that can endure the stress brought about by the products themselves. The microorganisms that are easiest to genetically manipulate for these endeavors (e.g. Escherichia coli) are often afflicted by an undesirable sensitivity to the very product that they are engineered to synthesize. In this context, we have examined the resistance to the stress arising from ethanol synthesis and/or its addition to cultures of recombinant Pseudomonas putida, using as a benchmark the same trait in an E. coli strain. To this end, ethanologenic strains of these two species were constructed by functionally expressing pdc (pyruvate decarboxylase) and adhB (alcohol dehydrogenase) from Zymomonas mobilis. Recombinants were compared under anoxic conditions as ethanol producers, and cell survival, stress resistance, and phenotypic stability were quantified in each case. P. putida consistently outperformed E. coli in every ethanol tolerance test conducted - whether the alcohol was produced endogenously or added exogenously. These results highlight the value of this bacterium as a microbial cell factory for the production of biofuels owing to its naturally pre-evolved ability to withstand different kinds of chemical stresses.
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Affiliation(s)
- Pablo I Nikel
- Systems and Synthetic Biology Program, Centro Nacional de Biotecnología (CNB-CSIC), Madrid 28049, Spain
| | - Víctor de Lorenzo
- Systems and Synthetic Biology Program, Centro Nacional de Biotecnología (CNB-CSIC), Madrid 28049, Spain.
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157
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Moreno AD, Ibarra D, Alvira P, Tomás-Pejó E, Ballesteros M. A review of biological delignification and detoxification methods for lignocellulosic bioethanol production. Crit Rev Biotechnol 2014; 35:342-54. [DOI: 10.3109/07388551.2013.878896] [Citation(s) in RCA: 121] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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158
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Lv YJ, Wang X, Ma Q, Bai X, Li BZ, Zhang W, Yuan YJ. Proteomic analysis reveals complex metabolic regulation in Saccharomyces cerevisiae cells against multiple inhibitors stress. Appl Microbiol Biotechnol 2014; 98:2207-21. [PMID: 24442506 DOI: 10.1007/s00253-014-5519-8] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2013] [Revised: 12/20/2013] [Accepted: 12/28/2013] [Indexed: 11/24/2022]
Abstract
Toxic compounds including acids, furans, and phenols (AFP) were generated from the pretreatment of lignocellulose. We cultivated Saccharomyces cerevisiae cells in a batch mode, besides the cell culture of original yeast strain in AFP-free medium which was referred as C0, three independent subcultures were cultivated under multiple inhibitors AFP and were referred as C1, C2, and C3 in time sequence. Comparing to C0, the cell density was lowered while the ethanol yield was maintained stably in the three yeast cultures under AFP stress, and the lag phase of C1 was extended while the lag phases of C2 and C3 were not extended. In proteomic analysis, 194 and 215 unique proteins were identified as differently expressed proteins at lag phase and exponential phase, respectively. Specifically, the yeast cells co-regulated protein folding and protein synthesis process to prevent the generation of misfolded proteins and to save cellular energy, they increased the activity of glycolysis, redirected metabolic flux towards phosphate pentose pathway and the biosynthesis of ethanol instead of the biosynthesis of glycerol and acetic acid, and they upregulated several oxidoreductases especially at lag phase and induced programmed cell death at exponential phase. When the yeast cells were cultivated under AFP stress, the new metabolism homeostasis in favor of cellular energy and redox homeostasis was generated in C1, then it was inherited and optimized in C2 and C3, enabling the yeast cells in C2 and C3 to enter the exponential phase in a short period after inoculation, which thus significantly shortened the fermentation time.
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Affiliation(s)
- Ya-Jin Lv
- Key Laboratory of Systems Bioengineering, Ministry of Education, Tianjin University, Tianjin, 300072, People's Republic of China
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159
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El-Ahmady N, Deraz S, Khalil A. Bioethanol Production from Lignocellulosic Feedstocks Based on Enzymatic Hydrolysis:
Current Status and Recent Developments. ACTA ACUST UNITED AC 2013. [DOI: 10.3923/biotech.2014.1.21] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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160
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Jin X, Ning Y. Laccase production optimization by response surface methodology with Aspergillus fumigatus AF1 in unique inexpensive medium and decolorization of different dyes with the crude enzyme or fungal pellets. JOURNAL OF HAZARDOUS MATERIALS 2013; 262:870-877. [PMID: 24140539 DOI: 10.1016/j.jhazmat.2013.09.024] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2013] [Revised: 08/13/2013] [Accepted: 09/11/2013] [Indexed: 06/02/2023]
Abstract
In the present study, alkaline pretreatment was applied for the enhanced laccase production from rice straw. Various process parameters including sodium hydroxide concentration, pH and fermentation temperature were optimized via response surface methodology (RSM) with a Box-Behnken design (BBD). Through regression analysis, it was found that laccase activity was well fitted by a quadratic polynomial equation (R(2)=0.998, Adj R(2)=0.995), and the fermentation temperature was the most significant factor influencing laccase activity. The optimized process conditions found were NaOH concentration of 0.39 mol L(-1), pH 3.12 and temperature 25.43 °C, under which laccase activity reached 142,198 ± 3586 U L(-1). Further studies were carried out to probe different dyes decolorization ability of laccase produced by Aspergillus fumigatus, A. fumigatus pellets and whole fermentation broth (WFB) using sodium hydroxide pretreated rice straw as sole carbon source. Results showed that pure laccase demonstrate limited decolorization ability to all the studied dyes, while crude laccase, A. fumigatus pellets and WFB exhibit significant decolorization ability to all the studied dyes with WFB being the most excellent one. Effectiveness of degradation was confirmed by uv-vis and phytotoxicity studies, which indicated that A. fumigatus transformed the dyes into non-toxic metabolites.
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Affiliation(s)
- Xianchun Jin
- School of Sciences, Henan Agricultural University, 450002, China.
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161
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Moreno AD, Tomás-Pejó E, Ibarra D, Ballesteros M, Olsson L. Fed-batch SSCF using steam-exploded wheat straw at high dry matter consistencies and a xylose-fermenting Saccharomyces cerevisiae strain: effect of laccase supplementation. BIOTECHNOLOGY FOR BIOFUELS 2013; 6:160. [PMID: 24219973 PMCID: PMC3843514 DOI: 10.1186/1754-6834-6-160] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/03/2013] [Accepted: 10/29/2013] [Indexed: 05/15/2023]
Abstract
BACKGROUND Lignocellulosic bioethanol is expected to play an important role in fossil fuel replacement in the short term. Process integration, improvements in water economy, and increased ethanol titers are key considerations for cost-effective large-scale production. The use of whole steam-pretreated slurries under high dry matter (DM) conditions and conversion of all fermentable sugars offer promising alternatives to achieve these goals. RESULTS Wheat straw slurry obtained from steam explosion showed high concentrations of degradation compounds, hindering the fermentation performance of the evolved xylose-recombinant Saccharomyces cerevisiae KE6-12 strain. Fermentability tests using the liquid fraction showed a higher number of colony-forming units (CFU) and higher xylose consumption rates when treating the medium with laccase. During batch simultaneous saccharification and co-fermentation (SSCF) processes, cell growth was totally inhibited at 12% DM (w/v) in untreated slurries. However, under these conditions laccase treatment prior to addition of yeast reduced the total phenolic content of the slurry and enabled the fermentation. During this process, an ethanol concentration of 19 g/L was obtained, corresponding to an ethanol yield of 39% of the theoretical yield. By changing the operation from batch mode to fed-batch mode, the concentration of inhibitors at the start of the process was reduced and 8 g/L of ethanol were obtained in untreated slurries with a final consistency of 16% DM (w/v). When fed-batch SSCF medium was supplemented with laccase 33 hours after yeast inoculation, no effect on ethanol yield or cell viability was found compared to untreated fermentations. However, if the laccase supplementation (21 hours after yeast inoculation) took place before the first addition of substrate (at 25 hours), improved cell viability and an increased ethanol titer of up to 32 g/L (51% of the theoretical) were found. CONCLUSIONS Laccase treatment in SSCF processes reduces the inhibitory effect that degradation compounds have on the fermenting microorganism. Furthermore, in combination with fed-batch operational mode, laccase supplementation allows the fermentation of wheat straw slurry at high DM consistencies, improving final ethanol concentrations and yields.
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Affiliation(s)
- Antonio D Moreno
- Instituto IMDEA Energía, Biotechnological Processes for Energy Production Unit, Móstoles 28935, Spain
- Department of Chemical and Biological Engineering, Industrial Biotechnology, Chalmers University of Technology, Göteborg SE-41296, Sweden
| | - Elia Tomás-Pejó
- Department of Chemical and Biological Engineering, Industrial Biotechnology, Chalmers University of Technology, Göteborg SE-41296, Sweden
| | - David Ibarra
- INIA-CIFOR, Forestry Products Department, Cellulose and Paper Laboratories, Madrid 28040, Spain
| | - Mercedes Ballesteros
- Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas, Biofuels Unit, Madrid 28040, Spain
| | - Lisbeth Olsson
- Department of Chemical and Biological Engineering, Industrial Biotechnology, Chalmers University of Technology, Göteborg SE-41296, Sweden
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162
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Kim SR, Park YC, Jin YS, Seo JH. Strain engineering of Saccharomyces cerevisiae for enhanced xylose metabolism. Biotechnol Adv 2013; 31:851-61. [DOI: 10.1016/j.biotechadv.2013.03.004] [Citation(s) in RCA: 140] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2012] [Revised: 02/23/2013] [Accepted: 03/04/2013] [Indexed: 12/27/2022]
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163
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Pardo I, Chanagá X, Vicente AI, Alcalde M, Camarero S. New colorimetric screening assays for the directed evolution of fungal laccases to improve the conversion of plant biomass. BMC Biotechnol 2013; 13:90. [PMID: 24159930 PMCID: PMC4015961 DOI: 10.1186/1472-6750-13-90] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2013] [Accepted: 10/23/2013] [Indexed: 11/20/2022] Open
Abstract
Background Fungal laccases are multicopper oxidases with huge applicability in different sectors. Here, we describe the development of a set of high-throughput colorimetric assays for screening laccase libraries in directed evolution studies. Results Firstly, we designed three colorimetric assays based on the oxidation of sinapic acid, acetosyringone and syringaldehyde with λmax of 512, 520 and 370 nm, respectively. These syringyl-type phenolic compounds are released during the degradation of lignocellulose and can act as laccase redox mediators. The oxidation of the three compounds by low and high-redox potential laccases evolved in Saccharomyces cerevisiae produced quantifiable and linear responses, with detection limits around 1 mU/mL and CV values below 16%. The phenolic substrates were also suitable for pre-screening mutant libraries on solid phase format. Intense colored-halos were developed around the yeast colonies secreting laccase. Furthermore, the oxidation of violuric acid to its iminoxyl radical (λmax of 515 nm and CV below 15%) was devised as reporter assay for laccase redox potential during the screening of mutant libraries from high-redox potential laccases. Finally, we developed three dye-decolorizing assays based on the enzymatic oxidation of Methyl Orange (470 nm), Evans Blue (605 nm) and Remazol Brilliant Blue (640 nm) giving up to 40% decolorization yields and CV values below 18%. The assays were reliable for direct measurement of laccase activity or to indirectly explore the oxidation of mediators that do not render colored products (but promote dye decolorization). Every single assay reported in this work was tested by exploring mutant libraries created by error prone PCR of fungal laccases secreted by yeast. Conclusions The high-throughput screening methods reported in this work could be useful for engineering laccases for different purposes. The assays based on the oxidation of syringyl-compounds might be valuable tools for tailoring laccases precisely enhanced to aid biomass conversion processes. The violuric assay might be useful to preserve the redox potential of laccase whilst evolving towards new functions. The dye-decolorizing assays are useful for engineering ad hoc laccases for detoxification of textile wastewaters, or as indirect assays to explore laccase activity on other natural mediators.
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Affiliation(s)
| | | | | | | | - Susana Camarero
- Centro de Investigaciones Biológicas, CSIC, Ramiro de Maeztu 9, 28040 Madrid, Spain.
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164
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Ethanol from laccase-detoxified lignocellulose by the thermotolerant yeast Kluyveromyces marxianus—Effects of steam pretreatment conditions, process configurations and substrate loadings. Biochem Eng J 2013. [DOI: 10.1016/j.bej.2013.07.006] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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165
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Moreno AD, Tomás-Pejó E, Ibarra D, Ballesteros M, Olsson L. In situ laccase treatment enhances the fermentability of steam-exploded wheat straw in SSCF processes at high dry matter consistencies. BIORESOURCE TECHNOLOGY 2013; 143:337-43. [PMID: 23811522 DOI: 10.1016/j.biortech.2013.06.011] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/24/2013] [Revised: 05/31/2013] [Accepted: 06/03/2013] [Indexed: 05/21/2023]
Abstract
This work evaluates the in situ detoxification of inhibitory lignocellulosic broths by laccases to facilitate their fermentation by the xylose-consuming Saccharomyces cerevisiae F12. Treatment of wheat straw slurries with laccases prior to SSCF processes decreased the total phenolic content by 50-80%, reducing the lag phase and increasing the cell viability. After laccase treatment, a negative impact on enzymatic hydrolysis was observed. This effect, together with the low enzymatic hydrolysis yields when increasing consistency, resulted in a decrease in final ethanol yields. Furthermore, when using high substrate loading (20% DM (w/v)), high concentration of inhibitors prevailed in broths and the absence of an extra nitrogen source led to a total cell growth inhibition within the first 24h in non-treated samples. This inhibition of growth at 20% DM (w/v) was overcome by laccase treatment with no addition of nitrogen, allowing S. cerevisiae F12 to produce more than 22 g/L of ethanol.
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Affiliation(s)
- Antonio D Moreno
- Instituto IMDEA Energía, Biotechnology Processes for Energy Production Unit, 28935 Móstoles, Spain
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166
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Pu X, Qu X, Chen F, Bao J, Zhang G, Luo Y. Camptothecin-producing endophytic fungus Trichoderma atroviride LY357: isolation, identification, and fermentation conditions optimization for camptothecin production. Appl Microbiol Biotechnol 2013; 97:9365-75. [DOI: 10.1007/s00253-013-5163-8] [Citation(s) in RCA: 70] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2013] [Revised: 07/26/2013] [Accepted: 07/29/2013] [Indexed: 10/26/2022]
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167
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Kim H, Ra CH, Kim SK. Ethanol production from seaweed (Undaria pinnatifida) using yeast acclimated to specific sugars. BIOTECHNOL BIOPROC E 2013. [DOI: 10.1007/s12257-013-0051-8] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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168
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Ibraheem O, Ndimba BK. Molecular adaptation mechanisms employed by ethanologenic bacteria in response to lignocellulose-derived inhibitory compounds. Int J Biol Sci 2013; 9:598-612. [PMID: 23847442 PMCID: PMC3708040 DOI: 10.7150/ijbs.6091] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2013] [Accepted: 04/26/2013] [Indexed: 11/12/2022] Open
Abstract
Current international interest in finding alternative sources of energy to the diminishing supplies of fossil fuels has encouraged research efforts in improving biofuel production technologies. In countries which lack sufficient food, the use of sustainable lignocellulosic feedstocks, for the production of bioethanol, is an attractive option. In the pre-treatment of lignocellulosic feedstocks for ethanol production, various chemicals and/or enzymatic processes are employed. These methods generally result in a range of fermentable sugars, which are subjected to microbial fermentation and distillation to produce bioethanol. However, these methods also produce compounds that are inhibitory to the microbial fermentation process. These compounds include products of sugar dehydration and lignin depolymerisation, such as organic acids, derivatised furaldehydes and phenolic acids. These compounds are known to have a severe negative impact on the ethanologenic microorganisms involved in the fermentation process by compromising the integrity of their cell membranes, inhibiting essential enzymes and negatively interact with their DNA/RNA. It is therefore important to understand the molecular mechanisms of these inhibitions, and the mechanisms by which these microorganisms show increased adaptation to such inhibitors. Presented here is a concise overview of the molecular adaptation mechanisms of ethanologenic bacteria in response to lignocellulose-derived inhibitory compounds. These include general stress response and tolerance mechanisms, which are typically those that maintain intracellular pH homeostasis and cell membrane integrity, activation/regulation of global stress responses and inhibitor substrate-specific degradation pathways. We anticipate that understanding these adaptation responses will be essential in the design of 'intelligent' metabolic engineering strategies for the generation of hyper-tolerant fermentation bacteria strains.
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Affiliation(s)
- Omodele Ibraheem
- Research and Services Unit, Agricultural Research Council/Infruitech & The University of Western Cape, Biotechnology Department, Private Bag X17, Bellville, Cape Town, South Africa
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169
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Skerker JM, Leon D, Price MN, Mar JS, Tarjan DR, Wetmore KM, Deutschbauer AM, Baumohl JK, Bauer S, Ibáñez AB, Mitchell VD, Wu CH, Hu P, Hazen T, Arkin AP. Dissecting a complex chemical stress: chemogenomic profiling of plant hydrolysates. Mol Syst Biol 2013; 9:674. [PMID: 23774757 PMCID: PMC3964314 DOI: 10.1038/msb.2013.30] [Citation(s) in RCA: 69] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2012] [Accepted: 05/12/2013] [Indexed: 11/09/2022] Open
Abstract
Complex chemical stress arises during the production of biofuels. Large-scale mutant fitness profiling was used to identify bacterial and yeast tolerance genes and to model fitness in a complex hydrolysate mixture. The resulting model can be used to engineer more tolerant strains. ![]()
Genome-wide fitness profiling was used to identify plant hydrolysate tolerance genes in Zymomonas mobilis and Saccharomyces cerevisiae. We modeled fitness in hydrolysate as a mixture of fitness in its components. Outliers in our model led to the identification of a previously unknown component of hydrolysate. Overexpression of a Z. mobilis tolerance gene of unknown function improved ethanol productivity in plant hydrolysate.
The efficient production of biofuels from cellulosic feedstocks will require the efficient fermentation of the sugars in hydrolyzed plant material. Unfortunately, plant hydrolysates also contain many compounds that inhibit microbial growth and fermentation. We used DNA-barcoded mutant libraries to identify genes that are important for hydrolysate tolerance in both Zymomonas mobilis (44 genes) and Saccharomyces cerevisiae (99 genes). Overexpression of a Z. mobilis tolerance gene of unknown function (ZMO1875) improved its specific ethanol productivity 2.4-fold in the presence of miscanthus hydrolysate. However, a mixture of 37 hydrolysate-derived inhibitors was not sufficient to explain the fitness profile of plant hydrolysate. To deconstruct the fitness profile of hydrolysate, we profiled the 37 inhibitors against a library of Z. mobilis mutants and we modeled fitness in hydrolysate as a mixture of fitness in its components. By examining outliers in this model, we identified methylglyoxal as a previously unknown component of hydrolysate. Our work provides a general strategy to dissect how microbes respond to a complex chemical stress and should enable further engineering of hydrolysate tolerance.
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Affiliation(s)
- Jeffrey M Skerker
- Energy Biosciences Institute, University of California, Berkeley, CA, USA
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Moreno AD, Ibarra D, Ballesteros I, González A, Ballesteros M. Comparing cell viability and ethanol fermentation of the thermotolerant yeast Kluyveromyces marxianus and Saccharomyces cerevisiae on steam-exploded biomass treated with laccase. BIORESOURCE TECHNOLOGY 2013; 135:239-45. [PMID: 23265821 DOI: 10.1016/j.biortech.2012.11.095] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/29/2012] [Revised: 11/08/2012] [Accepted: 11/10/2012] [Indexed: 05/13/2023]
Abstract
In this study, the thermotolerant yeast Kluyveromyces marxianus CECT 10875 was compared to the industrial strain Saccharomyces cerevisiae Ethanol Red for lignocellulosic ethanol production. For it, whole slurry from steam-exploded wheat straw was used as raw material, and two process configurations, simultaneous saccharification and fermentation (SSF) and presaccharification and simultaneous saccharification and fermentation (PSSF), were evaluated. Compared to S. cerevisiae, which was able to produce ethanol in both process configurations, K. marxianus was inhibited, and neither growth nor ethanol production occurred during the processes. However, laccase treatment of the whole slurry removed specifically lignin phenols from the overall inhibitory compounds present in the slurry and triggered the fermentation by K. marxianus, attaining final ethanol concentrations and yields comparable to those obtained by S. cerevisiae.
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Affiliation(s)
- Antonio D Moreno
- IMDEA Energía, Biotechnological Processes for Energy Production Unit, Móstoles, Madrid 28935, Spain
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171
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Xiao LP, Shi ZJ, Xu F, Sun RC. Hydrothermal treatment and enzymatic hydrolysis of Tamarix ramosissima: evaluation of the process as a conversion method in a biorefinery concept. BIORESOURCE TECHNOLOGY 2013; 135:73-81. [PMID: 23127831 DOI: 10.1016/j.biortech.2012.08.143] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/10/2012] [Revised: 08/29/2012] [Accepted: 08/30/2012] [Indexed: 06/01/2023]
Abstract
The present work investigated the effects of hydrothermal treatment (HTT) of Tamarix ramosissima by determination of sugar and inhibitor formation in the liquid fraction, and chemical and morphological changes of the pretreated solid material coupled with an evaluation of enzymatic hydrolysis. HTT was carried out in a batch reactor system at a maximal temperature (TMAX 180-240 °C) and evaluated for severities logRo ranging from 2.40 to 4.17. The liquid fractions were analyzed by HPLC, GPC, and GC-MS. The morphology and composition of the solid residues were characterized using an array of techniques, such as SEM, XRD, BET surface area, and CP/MAS (13)C NMR. Using a variety of tools, we have developed a better understanding of how HTT process affects biomass structure and cellulose properties that impact on its digestibility. These results provided new insights into the factors limiting enzymatic digestibility and mechanism of biomass deconstruction during hydrothermal process.
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Affiliation(s)
- Ling-Ping Xiao
- Institute of Biomass Chemistry and Technology, Beijing Forestry University, Beijing 100083, China
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172
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Iwaki A, Ohnuki S, Suga Y, Izawa S, Ohya Y. Vanillin inhibits translation and induces messenger ribonucleoprotein (mRNP) granule formation in saccharomyces cerevisiae: application and validation of high-content, image-based profiling. PLoS One 2013; 8:e61748. [PMID: 23637899 PMCID: PMC3634847 DOI: 10.1371/journal.pone.0061748] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2013] [Accepted: 03/13/2013] [Indexed: 11/18/2022] Open
Abstract
Vanillin, generated by acid hydrolysis of lignocellulose, acts as a potent inhibitor of the growth of the yeast Saccharomyces cerevisiae. Here, we investigated the cellular processes affected by vanillin using high-content, image-based profiling. Among 4,718 non-essential yeast deletion mutants, the morphology of those defective in the large ribosomal subunit showed significant similarity to that of vanillin-treated cells. The defects in these mutants were clustered in three domains of the ribosome: the mRNA tunnel entrance, exit and backbone required for small subunit attachment. To confirm that vanillin inhibited ribosomal function, we assessed polysome and messenger ribonucleoprotein granule formation after treatment with vanillin. Analysis of polysome profiles showed disassembly of the polysomes in the presence of vanillin. Processing bodies and stress granules, which are composed of non-translating mRNAs and various proteins, were formed after treatment with vanillin. These results suggest that vanillin represses translation in yeast cells.
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Affiliation(s)
- Aya Iwaki
- The Department of Applied Biology, Graduate School of Science and Technology, Kyoto Institute of Technology, Matsugasaki, Kyoto, Japan
| | - Shinsuke Ohnuki
- The Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, Kashiwa, Chiba, Japan
| | - Yohei Suga
- The Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, Kashiwa, Chiba, Japan
| | - Shingo Izawa
- The Department of Applied Biology, Graduate School of Science and Technology, Kyoto Institute of Technology, Matsugasaki, Kyoto, Japan
| | - Yoshikazu Ohya
- The Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, Kashiwa, Chiba, Japan
- * E-mail:
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173
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Heredia-Olea E, Pérez-Carrillo E, Serna-Saldívar SO. Production of ethanol from sweet sorghum bagasse pretreated with different chemical and physical processes and saccharified with fiber degrading enzymes. BIORESOURCE TECHNOLOGY 2013; 134:386-90. [PMID: 23489562 DOI: 10.1016/j.biortech.2013.01.162] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/27/2012] [Revised: 01/28/2013] [Accepted: 01/29/2013] [Indexed: 05/15/2023]
Abstract
The C5 and C6 sugars generated from sweet sorghum bagasse pretreated with five different chemical or physical schemes and then further hydrolyzed with a fibrolytic cocktail were determined. Hydrolysates were fermented with three yeast strains in order to determine which combination generated the highest amount of bioethanol. The bagasse only treated with the enzyme complex generated 50% of the total C5 and C6 sugars available. The pressure-cooked and extruded pretreatments further hydrolyzed with the enzymes generated 17% more sugars compared to the enzyme alone treatment. The enzyme increased the total sugar content in approximately 40% in the three acid pretreated hydrolysates. Among the different pretreatments, only the extrusion process did not generate inhibitors acetic acid, furfural and 5-hydroxymethylfurfural. At 24 h fermentation, the strains Saccharomyces cerevisiae and Issatchenkia orientalis produced, respectively 183.9 and 209.2 mg ethanol/g dry bagasse previously treated with HCl and enzymes.
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Affiliation(s)
- Erick Heredia-Olea
- Centro de Biotecnología-FEMSA, Tecnológico de Monterrey, Av., Eugenio Garza Sada 2501 Sur, CP 64849, Monterrey, NL, Mexico
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174
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Improving Escherichia coli FucO for furfural tolerance by saturation mutagenesis of individual amino acid positions. Appl Environ Microbiol 2013; 79:3202-8. [PMID: 23475621 DOI: 10.1128/aem.00149-13] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Furfural is an inhibitory side product formed during the depolymerization of hemicellulose with mineral acids. In Escherichia coli, furfural tolerance can be increased by expressing the native fucO gene (encoding lactaldehyde oxidoreductase). This enzyme also catalyzes the NADH-dependent reduction of furfural to the less toxic alcohol. Saturation mutagenesis was combined with growth-based selection to isolate a mutated form of fucO that confers increased furfural tolerance. The mutation responsible, L7F, is located within the interfacial region of FucO homodimers, replacing the most abundant codon for leucine with the most abundant codon for phenylalanine. Plasmid expression of the mutant gene increased FucO activity by more than 10-fold compared to the wild-type fucO gene and doubled the rate of furfural metabolism during fermentation. No inclusion bodies were evident with either the native or the mutated gene. mRNA abundance for the wild-type and mutant fucO genes differed by less than 2-fold. The Km (furfural) for the mutant enzyme was 3-fold lower than that for the native enzyme, increasing efficiency at low substrate concentrations. The L7F mutation is located near the FucO N terminus, within the ribosomal binding region associated with translational initiation. Free-energy calculations for mRNA folding in this region (nucleotides -7 to +37) were weak for the native gene (-4.1 kcal mol(-1)) but weaker still for the fucO mutant (-1.0 to -0.1 kcal mol(-1)). The beneficial L7F mutation in FucO is proposed to increase furfural tolerance by improving gene expression and increasing enzyme effectiveness at low substrate levels.
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175
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Zhou F, Wang C, Wei J. Simultaneous acetic acid separation and monosaccharide concentration by reverse osmosis. BIORESOURCE TECHNOLOGY 2013; 131:349-356. [PMID: 23376199 DOI: 10.1016/j.biortech.2012.12.145] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/13/2012] [Revised: 12/18/2012] [Accepted: 12/21/2012] [Indexed: 06/01/2023]
Abstract
This study aimed to investigate the feasibility and efficiency of simultaneous acetic acid separation and sugar concentration in model lignocellulosic hydrolyzates by reverse osmosis. The effects of operation parameters such as pH, temperature, pressure and feed concentration on the solute retentions were examined with a synthetic xylose–glucose–acetic acid model solution. Results showed that the monosaccharides were almost completely rejected at above 20 bar, while the acetic acid retention increased with the increase in pH and pressure, and decreased with the temperature increase. The maximum separation factors of acetic acid over xylose and glucose reached as high as 211.5 and 228.4 at pH 2.93 (the initial pH of model lignocellulosic hydrolyzates), 40 °C and 20 bar. Furthermore, the concentration and diafiltration process were employed at optimal operation conditions. Consequently, a high sugar concentration and a beneficially lower acetic acid concentration were simultaneously achieved by reverse osmosis.
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Affiliation(s)
- Fanglei Zhou
- Key Laboratory for Green Chemical Process of Ministry of Education, Wuhan Institute of Technology, Xiongchu Avenue 693, Wuhan 430073, China
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176
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Gaykawad SS, Zha Y, Punt PJ, van Groenestijn JW, van der Wielen LAM, Straathof AJJ. Pervaporation of ethanol from lignocellulosic fermentation broth. BIORESOURCE TECHNOLOGY 2013; 129:469-476. [PMID: 23266848 DOI: 10.1016/j.biortech.2012.11.104] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/18/2012] [Revised: 11/21/2012] [Accepted: 11/23/2012] [Indexed: 06/01/2023]
Abstract
Pervaporation can be applied in ethanol production from lignocellulosic biomass. Hydrophobic pervaporation, using a commercial PDMS membrane, was employed to concentrate the ethanol produced by fermentation of lignocellulosic hydrolysate. To our knowledge, this is the first report describing this. Pervaporation carried out with three different lignocellulosic fermentation broths reduced the membrane performance by 17-20% as compared to a base case containing only 3 wt.% ethanol in water. The membrane fouling caused by these fermentation broths was irreversible. Solutions containing model lignocellulosic components were tested during pervaporation at the same conditions. A total flux decrease of 12-15%, as compared to the base case, was observed for each component except for furfural. Catechol was found to be most fouling component whereas furfural permeated through the membrane and increased the total flux. The membrane selectivity increased in the presence of fermentation broth but remained unchanged for all selected components.
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Affiliation(s)
- Sushil S Gaykawad
- Department of Biotechnology, Delft University of Technology, Julianalaan 67, 2628 BC, Delft, The Netherlands
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177
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178
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Jönsson LJ, Alriksson B, Nilvebrant NO. Bioconversion of lignocellulose: inhibitors and detoxification. BIOTECHNOLOGY FOR BIOFUELS 2013; 6:16. [PMID: 23356676 PMCID: PMC3574029 DOI: 10.1186/1754-6834-6-16] [Citation(s) in RCA: 611] [Impact Index Per Article: 55.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/05/2012] [Accepted: 01/16/2013] [Indexed: 05/17/2023]
Abstract
Bioconversion of lignocellulose by microbial fermentation is typically preceded by an acidic thermochemical pretreatment step designed to facilitate enzymatic hydrolysis of cellulose. Substances formed during the pretreatment of the lignocellulosic feedstock inhibit enzymatic hydrolysis as well as microbial fermentation steps. This review focuses on inhibitors from lignocellulosic feedstocks and how conditioning of slurries and hydrolysates can be used to alleviate inhibition problems. Novel developments in the area include chemical in-situ detoxification by using reducing agents, and methods that improve the performance of both enzymatic and microbial biocatalysts.
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Affiliation(s)
- Leif J Jönsson
- Department of Chemistry, Umeå University, Umeå SE-901 87, Sweden
| | - Björn Alriksson
- Processum Biorefinery Initiative AB, Örnsköldsvik, SE-891 22, Sweden
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179
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Biotechnological production of ethanol from renewable resources by Neurospora crassa: an alternative to conventional yeast fermentations? Appl Microbiol Biotechnol 2013; 97:1457-73. [DOI: 10.1007/s00253-012-4655-2] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2012] [Revised: 12/11/2012] [Accepted: 12/13/2012] [Indexed: 12/21/2022]
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180
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Jin M, Sarks C, Gunawan C, Bice BD, Simonett SP, Avanasi Narasimhan R, Willis LB, Dale BE, Balan V, Sato TK. Phenotypic selection of a wild Saccharomyces cerevisiae strain for simultaneous saccharification and co-fermentation of AFEX™ pretreated corn stover. BIOTECHNOLOGY FOR BIOFUELS 2013; 6:108. [PMID: 23890073 PMCID: PMC3729497 DOI: 10.1186/1754-6834-6-108] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2012] [Accepted: 07/25/2013] [Indexed: 05/09/2023]
Abstract
BACKGROUND Simultaneous saccharification and co-fermentation (SSCF) process involves enzymatic hydrolysis of pretreated lignocellulosic biomass and fermentation of glucose and xylose in one bioreactor. The optimal temperatures for enzymatic hydrolysis are higher than the standard fermentation temperature of ethanologenic Saccharomyces cerevisiae. Moreover, degradation products resulting from biomass pretreatment impair fermentation of sugars, especially xylose, and can synergize with high temperature stress. One approach to resolve both concerns is to utilize a strain background with innate tolerance to both elevated temperatures and degradation products. RESULTS In this study, we screened a panel of 108 wild and domesticated Saccharomyces cerevisiae strains isolated from a wide range of environmental niches. One wild strain was selected based on its growth tolerance to simultaneous elevated temperature and AFEX™ (Ammonia Fiber Expansion) degradation products. After engineering the strain with two copies of the Scheffersomyces stipitis xylose reductase, xylitol dehydrogenase and xylulokinase genes, we compared the ability of this engineered strain to the benchmark 424A(LNH-ST) strain in ethanol production and xylose fermentation in standard lab medium and AFEX pretreated corn stover (ACS) hydrolysates, as well as in SSCF of ACS at different temperatures. In SSCF of 9% (w/w) glucan loading ACS at 35°C, the engineered strain showed higher cell viabilities and produced a similar amount of ethanol (51.3 g/L) compared to the benchmark 424A(LNH-ST) strain. CONCLUSION These results validate our approach in the selection of wild Saccharomyces cerevisiae strains with thermo-tolerance and degradation products tolerance properties for lignocellulosic biofuel production. The wild and domesticated yeast strains phenotyped in this work are publically available for others to use as genetic backgrounds for fermentation of their pretreated biomass at elevated temperatures.
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Affiliation(s)
- Mingjie Jin
- Biomass Conversion Research Laboratory (BCRL), Department of Chemical Engineering and Materials Science, Michigan State University, 3900 Collins Road, Lansing, MI 48910, USA
- DOE Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI 48824, USA
| | - Cory Sarks
- Biomass Conversion Research Laboratory (BCRL), Department of Chemical Engineering and Materials Science, Michigan State University, 3900 Collins Road, Lansing, MI 48910, USA
- DOE Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI 48824, USA
| | - Christa Gunawan
- Biomass Conversion Research Laboratory (BCRL), Department of Chemical Engineering and Materials Science, Michigan State University, 3900 Collins Road, Lansing, MI 48910, USA
- DOE Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI 48824, USA
| | - Benjamin D Bice
- DOE Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, 1552 University Ave, Madison, WI 53726, USA
| | - Shane P Simonett
- Department of Bacteriology, University of Wisconsin-Madison, 1550 Linden Dr, Madison, WI 53706, USA
| | - Ragothaman Avanasi Narasimhan
- DOE Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, 1552 University Ave, Madison, WI 53726, USA
| | - Laura B Willis
- DOE Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, 1552 University Ave, Madison, WI 53726, USA
- Department of Bacteriology, University of Wisconsin-Madison, 1550 Linden Dr, Madison, WI 53706, USA
- U.S. Department of Agriculture, Forest Products Laboratory, 1 Gifford Pinchot Dr, Madison, WI 53726, USA
| | - Bruce E Dale
- Biomass Conversion Research Laboratory (BCRL), Department of Chemical Engineering and Materials Science, Michigan State University, 3900 Collins Road, Lansing, MI 48910, USA
- DOE Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI 48824, USA
| | - Venkatesh Balan
- Biomass Conversion Research Laboratory (BCRL), Department of Chemical Engineering and Materials Science, Michigan State University, 3900 Collins Road, Lansing, MI 48910, USA
- DOE Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI 48824, USA
| | - Trey K Sato
- DOE Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, 1552 University Ave, Madison, WI 53726, USA
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181
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Bioconversion of sugarcane biomass into ethanol: an overview about composition, pretreatment methods, detoxification of hydrolysates, enzymatic saccharification, and ethanol fermentation. J Biomed Biotechnol 2012; 2012:989572. [PMID: 23251086 PMCID: PMC3516358 DOI: 10.1155/2012/989572] [Citation(s) in RCA: 139] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2012] [Accepted: 10/19/2012] [Indexed: 11/17/2022] Open
Abstract
Depleted supplies of fossil fuel, regular price hikes of gasoline, and environmental damage have necessitated the search for economic and eco-benign alternative of gasoline. Ethanol is produced from food/feed-based substrates (grains, sugars, and molasses), and its application as an energy source does not seem fit for long term due to the increasing fuel, food, feed, and other needs. These concerns have enforced to explore the alternative means of cost competitive and sustainable supply of biofuel. Sugarcane residues, sugarcane bagasse (SB), and straw (SS) could be the ideal feedstock for the second-generation (2G) ethanol production. These raw materials are rich in carbohydrates and renewable and do not compete with food/feed demands. However, the efficient bioconversion of SB/SS (efficient pretreatment technology, depolymerization of cellulose, and fermentation of released sugars) remains challenging to commercialize the cellulosic ethanol. Among the technological challenges, robust pretreatment and development of efficient bioconversion process (implicating suitable ethanol producing strains converting pentose and hexose sugars) have a key role to play. This paper aims to review the compositional profile of SB and SS, pretreatment methods of cane biomass, detoxification methods for the purification of hydrolysates, enzymatic hydrolysis, and the fermentation of released sugars for ethanol production.
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182
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Lee KM, Kalyani D, Tiwari MK, Kim TS, Dhiman SS, Lee JK, Kim IW. Enhanced enzymatic hydrolysis of rice straw by removal of phenolic compounds using a novel laccase from yeast Yarrowia lipolytica. BIORESOURCE TECHNOLOGY 2012; 123:636-45. [PMID: 22960123 DOI: 10.1016/j.biortech.2012.07.066] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/13/2012] [Revised: 07/17/2012] [Accepted: 07/19/2012] [Indexed: 05/24/2023]
Abstract
An extracellular laccase-producing yeast was isolated from soil and identified as Yarrowia lipolytica by its morphology and by comparison of its internal transcribed spacer rDNA gene sequence. Extracellular laccase (YlLac) from Y. lipolytica was purified to homogeneity by anion-exchange and gel filtration chromatography. YlLac is a monomeric glycoprotein with 14% carbohydrate content and a molecular mass of 67kDa. It showed a higher catalytic efficiency towards 2,2'-Azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) (k(cat)/K(m)=19.3s(-1)μM(-1)) and 2,6-dimethoxyphenol (k(cat)/K(m)=13s(-1)μM(-1)) than any other reported laccase. This enzyme was able to oxidize phenolic compounds present in pretreated rice straw. Several parameters (temperature, enzyme concentration, and mediator compounds) to enhance removal of phenolic compounds from pretreated rice straw were optimized using response surface methodology. The use of YlLac for the removal of cellulase inhibitory compounds from biomass slurries was found to be a promising approach for improving the efficiency of biorefineries.
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Affiliation(s)
- Kyoung-Mi Lee
- Institute of SK-KU Biomaterials, Konkuk University, Seoul 143-701, Republic of Korea
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183
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Characterization of a Recombinant Flocculent Saccharomyces cerevisiae Strain That Co-Ferments Glucose and Xylose: II. Influence of pH and Acetic Acid on Ethanol Production. Appl Biochem Biotechnol 2012; 168:2094-104. [DOI: 10.1007/s12010-012-9920-4] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2012] [Accepted: 10/03/2012] [Indexed: 10/27/2022]
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184
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A TRP5/5-fluoroanthranilic acid counter-selection system for gene disruption in Candida guilliermondii. Curr Genet 2012; 58:245-54. [DOI: 10.1007/s00294-012-0377-3] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2012] [Revised: 05/02/2012] [Accepted: 05/06/2012] [Indexed: 10/28/2022]
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185
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Degradation and assimilation of aromatic compounds by Corynebacterium glutamicum: another potential for applications for this bacterium? Appl Microbiol Biotechnol 2012; 95:77-89. [DOI: 10.1007/s00253-012-4139-4] [Citation(s) in RCA: 91] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2012] [Revised: 04/24/2012] [Accepted: 04/24/2012] [Indexed: 11/26/2022]
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186
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Liu B, Hui J, Cheng YQ, Zhang X. Extractive fermentation for enhanced production of thailandepsin A from Burkholderia thailandensis E264 using polyaromatic adsorbent resin Diaion HP-20. ACTA ACUST UNITED AC 2012; 39:767-76. [DOI: 10.1007/s10295-011-1073-x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2011] [Accepted: 12/08/2011] [Indexed: 11/28/2022]
Abstract
Abstract
Thailandepsin A is natural product of Burkholderia thailandensis E264 with potent histone deacetylase inhibitory activities and promising anticancer activities. The titer of thailandepsin A is very low (less than 10 mg/l) from limited empirical fermentation. To facilitate preclinical evaluations and potentially clinical development of thailandepsin A, systematic optimization and extractive fermentation of thailandepsin A from B. thailandensis E264 culture in flasks were investigated in this pilot study. The main fermentation parameters—28°C, pH 7.0, inoculum ratio 1% (v/v), incubation duration 60 h, medium volume 26%, shaking speed 170 rpm, and chloroform as extracting solvent—were determined by single factor experiments. Polyaromatic adsorbent resin Diaion HP-20, when added at a concentration of 4% (w/v), was most effective to reduce feedback inhibition of thailandepsin A and to significantly increase the titer of target product. Central composite design was used to further optimize the fermentation medium for B. thailandensis E264. The optimized medium contains glucose 17.89 g/l, tryptone 34.98 g/l, potassium phosphate 24.84 g/l, and sodium citrate 0.01 g/l, which resulted in a large increase of the titer of thailandepsin A to 236.7 mg/l. Finally kinetic models based on the modified logistic and Luedeking–Piret equations were developed, delivering a good description of temporal variations of biomass, product, and substrate in the fermentation process, which could be used as references for developing large-scale fermentation.
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Affiliation(s)
- Bing Liu
- grid.16821.3c 0000000403688293 State Key Laboratory of Microbial Metabolism School of Life Sciences and Biotechnology, Shanghai Jiao Tong University 200240 Shanghai People’s Republic of China
| | - Junyuan Hui
- grid.16821.3c 0000000403688293 State Key Laboratory of Microbial Metabolism School of Life Sciences and Biotechnology, Shanghai Jiao Tong University 200240 Shanghai People’s Republic of China
| | - Yi-Qiang Cheng
- grid.267468.9 0000000106957223 Department of Biological Sciences University of Wisconsin–Milwaukee P.O. Box 413 53201 Milwaukee WI USA
- grid.267468.9 0000000106957223 Department of Chemistry and Biochemistry University of Wisconsin–Milwaukee P.O. Box 413 53201 Milwaukee WI USA
- ChinAm PharmaTech Wuhan Ltd. No. 666 Gaoxin Road, Wuhan East Lake Hi-Tech Development Zone 430079 Wuhan People’s Republic of China
| | - Xuehong Zhang
- grid.16821.3c 0000000403688293 State Key Laboratory of Microbial Metabolism School of Life Sciences and Biotechnology, Shanghai Jiao Tong University 200240 Shanghai People’s Republic of China
- ChinAm PharmaTech Wuhan Ltd. No. 666 Gaoxin Road, Wuhan East Lake Hi-Tech Development Zone 430079 Wuhan People’s Republic of China
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187
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Gagarinova A, Emili A. Genome-scale genetic manipulation methods for exploring bacterial molecular biology. MOLECULAR BIOSYSTEMS 2012; 8:1626-38. [PMID: 22517266 DOI: 10.1039/c2mb25040c] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Bacteria are diverse and abundant, playing key roles in human health and disease, the environment, and biotechnology. Despite progress in genome sequencing and bioengineering, much remains unknown about the functional organization of prokaryotes. For instance, roughly a third of the protein-coding genes of the best-studied model bacterium, Escherichia coli, currently lack experimental annotations. Systems-level experimental approaches for investigating the functional associations of bacterial genes and genetic structures are essential for defining the fundamental molecular biology of microbes, preventing the spread of antibacterial resistance in the clinic, and driving the development of future biotechnological applications. This review highlights recently introduced large-scale genetic manipulation and screening procedures for the systematic exploration of bacterial gene functions, molecular relationships, and the global organization of bacteria at the gene, pathway, and genome levels.
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Affiliation(s)
- Alla Gagarinova
- Department of Molecular Genetics, University of Toronto, Toronto, Canada
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188
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Increase in furfural tolerance in ethanologenic Escherichia coli LY180 by plasmid-based expression of thyA. Appl Environ Microbiol 2012; 78:4346-52. [PMID: 22504824 DOI: 10.1128/aem.00356-12] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Furfural is an inhibitory side product formed during the depolymerization of hemicellulose by mineral acids. Genomic libraries from three different bacteria (Bacillus subtilis YB886, Escherichia coli NC3, and Zymomonas mobilis CP4) were screened for genes that conferred furfural resistance on plates. Beneficial plasmids containing the thyA gene (coding for thymidylate synthase) were recovered from all three organisms. Expression of this key gene in the de novo pathway for dTMP biosynthesis improved furfural resistance on plates and during fermentation. A similar benefit was observed by supplementation with thymine, thymidine, or the combination of tetrahydrofolate and serine (precursors for 5,10-methylenetetrahydrofolate, the methyl donor for ThyA). Supplementation with deoxyuridine provided a small benefit, and deoxyribose was of no benefit for furfural tolerance. A combination of thymidine and plasmid expression of thyA was no more effective than either alone. Together, these results demonstrate that furfural tolerance is increased by approaches that increase the supply of pyrimidine deoxyribonucleotides. However, ThyA activity was not directly affected by the addition of furfural. Furfural has been previously shown to damage DNA in E. coli and to activate a cellular response to oxidative damage in yeast. The added burden of repairing furfural-damaged DNA in E. coli would be expected to increase the cellular requirement for dTMP. Increased expression of thyA (E. coli, B. subtilis, or Z. mobilis), supplementation of cultures with thymidine, and supplementation with precursors for 5,10-methylenetetrahydrofolate (methyl donor) are each proposed to increase furfural tolerance by increasing the availability of dTMP for DNA repair.
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189
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Biomass Converting Enzymes as Industrial Biocatalysts for Fuels and Chemicals: Recent Developments. Catalysts 2012. [DOI: 10.3390/catal2020244] [Citation(s) in RCA: 95] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
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190
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Kalyani D, Dhiman SS, Kim H, Jeya M, Kim IW, Lee JK. Characterization of a novel laccase from the isolated Coltricia perennis and its application to detoxification of biomass. Process Biochem 2012. [DOI: 10.1016/j.procbio.2012.01.013] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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191
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Laluce C, Schenberg ACG, Gallardo JCM, Coradello LFC, Pombeiro-Sponchiado SR. Advances and Developments in Strategies to Improve Strains of Saccharomyces cerevisiae and Processes to Obtain the Lignocellulosic Ethanol−A Review. Appl Biochem Biotechnol 2012; 166:1908-26. [DOI: 10.1007/s12010-012-9619-6] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2011] [Accepted: 02/16/2012] [Indexed: 10/28/2022]
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192
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Taylor MP, Mulako I, Tuffin M, Cowan D. Understanding physiological responses to pre-treatment inhibitors in ethanologenic fermentations. Biotechnol J 2012; 7:1169-81. [PMID: 22331581 DOI: 10.1002/biot.201100335] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2011] [Revised: 12/15/2011] [Accepted: 01/17/2012] [Indexed: 11/10/2022]
Abstract
Alcohol-based liquid fuels feature significantly in the political and social agendas of many countries, seeking energy sustainability. It is certain that ethanol will be the entry point for many sustainable processes. Conventional ethanol production using maize- and sugarcane-based carbohydrates with Saccharomyces cerevisiae is well established, while lignocellulose-based processes are receiving growing interest despite posing greater technical and scientific challenges. A significant challenge that arises from the chemical hydrolysis of lignocellulose is the generation of toxic compounds in parallel with the release of sugars. These compounds, collectively termed pre-treatment inhibitors, impair metabolic functionality and growth. Their removal, pre-fermentation or their abatement, via milder hydrolysis, are currently uneconomic options. It is widely acknowledged that a more cost effective strategy is to develop resistant process strains. Here we describe and classify common inhibitors and describe in detail the reported physiological responses that occur in second-generation strains, which include engineered yeast and mesophilic and thermophilic prokaryotes. It is suggested that a thorough understanding of tolerance to common pre-treatment inhibitors should be a major focus in ongoing strain engineering. This review is a useful resource for future metabolic engineering strategies.
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Affiliation(s)
- Mark P Taylor
- TMO Renewables Ltd., The Surrey Research Park, Guildford, UK
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193
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Moreno AD, Ibarra D, Fernández JL, Ballesteros M. Different laccase detoxification strategies for ethanol production from lignocellulosic biomass by the thermotolerant yeast Kluyveromyces marxianus CECT 10875. BIORESOURCE TECHNOLOGY 2012; 106:101-9. [PMID: 22197073 DOI: 10.1016/j.biortech.2011.11.108] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/08/2011] [Revised: 11/21/2011] [Accepted: 11/25/2011] [Indexed: 05/13/2023]
Abstract
In this work, laccase enzymes were evaluated to detoxify the whole slurry from steam-exploded wheat straw. For it, two different strategies, laccase treatment before or after enzymatic hydrolysis, were employed. The detoxification efficiency was analyzed on enzymatic hydrolysis and fermentation levels by the thermotolerant yeast Kluyveromyces marxianus. Laccases reduced phenolic compounds without affecting weak acids and furan derivates. A lower glucose recovery was observed when laccase treatments were carried out before enzymatic hydrolysis, phenomenon that was not showed after enzymatic hydrolysis. In contrast, both laccase treatment strategies enhanced ethanol concentrations, reducing significantly the lag phase of the yeast and allowing substrate loading increments of saccharification and fermentation broths.
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Affiliation(s)
- Antonio D Moreno
- Instituto IMDEA Energía, Biotechnological Processes for Energy Production Unit, Móstoles, Madrid 28933, Spain
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194
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195
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Wong KS, Huang Q, Au CH, Wang J, Kwan HS. Biodegradation of dyes and polyaromatic hydrocarbons by two allelic forms of Lentinula edodes laccase expressed from Pichia pastoris. BIORESOURCE TECHNOLOGY 2012; 104:157-164. [PMID: 22130082 DOI: 10.1016/j.biortech.2011.10.097] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/31/2011] [Revised: 10/26/2011] [Accepted: 10/28/2011] [Indexed: 05/31/2023]
Abstract
Laccases from basidiomycetes are efficient enzymes in the degradation of xenobiotics. In this study we aimed to provide an industrially relevant expression system for Lentinula edodes laccases, to characterize their enzymatic properties, and to evaluate their potential in bioremediation. Two 1573-bp allelic laccase genes from L. edodes L54 were cloned based on gene models in the genome sequence. A novel upstream consensus (GCTCCGA/CCGGAG) was proposed as an alternative signature sequence for laccases. Both alleles were overexpressed in Pichia pastoris, purified, and verified by zymograms. Kinetic analyses suggested an order of catalytic efficiency of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)>2,6-dimethoxyphenol>guaiacol>l-3,4-dihydroxyphenylalanine>catechol, and a stable range of working temperature below 40 °C. With the appropriate mediators, 1-hydroxybenzotriazole and 2,2,6,6-tetramethylpiperidine-1-oxyl, the recombinant enzymes could catalyze a 70-100% decolorization of selected dyes and a complete degradation of anthracene. These results laid a solid foundation for the use of L. edodes laccases in bioremediations and for improvement with protein engineering.
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Affiliation(s)
- Kin-Sing Wong
- School of Life Sciences, The Chinese University of Hong Kong, Shatin, Hong Kong.
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196
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Genetic engineering and enzyme research in lignocellulosic ethanol production. Protein Cell 2011; 2:776-7. [PMID: 22058031 DOI: 10.1007/s13238-011-1108-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/15/2022] Open
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197
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Bajwa PK, Phaenark C, Grant N, Zhang X, Paice M, Martin VJJ, Trevors JT, Lee H. Ethanol production from selected lignocellulosic hydrolysates by genome shuffled strains of Scheffersomyces stipitis. BIORESOURCE TECHNOLOGY 2011; 102:9965-9. [PMID: 21890342 DOI: 10.1016/j.biortech.2011.08.027] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/21/2011] [Revised: 07/30/2011] [Accepted: 08/03/2011] [Indexed: 05/23/2023]
Abstract
Two genome-shuffled Scheffersomyces stipitis strains, GS301 and GS302, exhibiting improved tolerance to hardwood spent sulphite liquor, were tested for growth and fermentation performance on three wood hydrolysates: (a) steam-pretreated enzymatically hydrolyzed poplar hydrolysate from Mascoma Canada, (b) steam pretreated poplar hydrolysate from University of British Columbia Forest Products Biotechnology Laboratory, and (c) mixed hardwoods pre-hydrolysate from FPInnovations (FPI). In the FPI hydrolysate, the wild type (WT) died off within 25 h, while GS301 and GS302 survived beyond 100 h. In fermentation tests, GS301 and GS302 completely utilized glucose and xylose in each hydrolysate and produced 0.39-1.4% (w/v) ethanol. In contrast, the WT did not utilize or poorly utilized glucose and xylose and produced non-detectable to trace amounts of ethanol. The results demonstrated cross tolerance of the mutants to inhibitors in three different wood hydrolysates and reinforced the utility of mating-based genome shuffling approach in industrial yeast strain improvement.
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Affiliation(s)
- Paramjit K Bajwa
- School of Environmental Sciences, University of Guelph, Guelph, Ontario, Canada
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198
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Wierckx N, Koopman F, Ruijssenaars HJ, de Winde JH. Microbial degradation of furanic compounds: biochemistry, genetics, and impact. Appl Microbiol Biotechnol 2011; 92:1095-105. [PMID: 22031465 PMCID: PMC3223595 DOI: 10.1007/s00253-011-3632-5] [Citation(s) in RCA: 103] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2011] [Revised: 09/29/2011] [Accepted: 10/06/2011] [Indexed: 11/16/2022]
Abstract
Microbial metabolism of furanic compounds, especially furfural and 5-hydroxymethylfurfural (HMF), is rapidly gaining interest in the scientific community. This interest can largely be attributed to the occurrence of toxic furanic aldehydes in lignocellulosic hydrolysates. However, these compounds are also widespread in nature and in human processed foods, and are produced in industry. Although several microorganisms are known to degrade furanic compounds, the variety of species is limited mostly to Gram-negative aerobic bacteria, with a few notable exceptions. Furanic aldehydes are highly toxic to microorganisms, which have evolved a wide variety of defense mechanisms, such as the oxidation and/or reduction to the furanic alcohol and acid forms. These oxidation/reduction reactions constitute the initial steps of the biological pathways for furfural and HMF degradation. Furfural degradation proceeds via 2-furoic acid, which is metabolized to the primary intermediate 2-oxoglutarate. HMF is converted, via 2,5-furandicarboxylic acid, into 2-furoic acid. The enzymes in these HMF/furfural degradation pathways are encoded by eight hmf genes, organized in two distinct clusters in Cupriavidus basilensis HMF14. The organization of the five genes of the furfural degradation cluster is highly conserved among microorganisms capable of degrading furfural, while the three genes constituting the initial HMF degradation route are organized in a highly diverse manner. The genetic and biochemical characterization of the microbial metabolism of furanic compounds holds great promises for industrial applications such as the biodetoxifcation of lignocellulosic hydrolysates and the production of value-added compounds such as 2,5-furandicarboxylic acid.
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199
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Parawira W. Enzyme research and applications in biotechnological intensification of biogas production. Crit Rev Biotechnol 2011; 32:172-86. [PMID: 21851320 DOI: 10.3109/07388551.2011.595384] [Citation(s) in RCA: 122] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Biogas technology provides an alternative source of energy to fossil fuels in many parts of the world. Using local resources such as agricultural crop remains, municipal solid wastes, market wastes and animal waste, energy (biogas), and manure are derived by anaerobic digestion. The hydrolysis process, where the complex insoluble organic materials are hydrolysed by extracellular enzymes, is a rate-limiting step for anaerobic digestion of high-solid organic solid wastes. Biomass pretreatment and hydrolysis are areas in need of drastic improvement for economic production of biogas from complex organic matter such as lignocellulosic material and sewage sludge. Despite development of pretreatment techniques, sugar release from complex biomass still remains an expensive and slow step, perhaps the most critical in the overall process. This paper gives an updated review of the biotechnological advances to improve biogas production by microbial enzymatic hydrolysis of different complex organic matter for converting them into fermentable structures. A number of authors have reported significant improvement in biogas production when crude and commercial enzymes are used in the pretreatment of complex organic matter. There have been studies on the improvement of biogas production from lignocellulolytic materials, one of the largest and renewable sources of energy on earth, after pretreatment with cellulases and cellulase-producing microorganisms. Lipids (characterised as oil, grease, fat, and free long chain fatty acids, LCFA) are a major organic compound in wastewater generated from the food processing industries and have been considered very difficult to convert into biogas. Improved methane yield has been reported in the literature when these lipid-rich wastewaters are pretreated with lipases and lipase-producing microorganisms. The enzymatic treatment of mixed sludge by added enzymes prior to anaerobic digestion has been shown to result in improved degradation of the sludge and an increase in methane production. Strategies for enzyme dosing to enhance anaerobic digestion of the different complex organic rich materials have been investigated. This review also highlights the various challenges and opportunities that exist to improve enzymatic hydrolysis of complex organic matter for biogas production. The arguments in favor of enzymes to pretreat complex biomass are compelling. The high cost of commercial enzyme production, however, still limits application of enzymatic hydrolysis in full-scale biogas production plants, although production of low-cost enzymes and genetic engineering are addressing this issue.
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Affiliation(s)
- Wilson Parawira
- Department of Applied Biology, Kigali Institute of Science and Technology, Rwanda.
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200
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Qi B, Luo J, Chen X, Hang X, Wan Y. Separation of furfural from monosaccharides by nanofiltration. BIORESOURCE TECHNOLOGY 2011; 102:7111-7118. [PMID: 21570829 DOI: 10.1016/j.biortech.2011.04.041] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/13/2011] [Revised: 04/13/2011] [Accepted: 04/16/2011] [Indexed: 05/30/2023]
Abstract
Furfural, found in the lignocellulosic prehydrolyzates at high concentration, is a strong inhibitor of growth and ethanol fermentation of Saccharomyces cerevisiae. Removal of furfural and concentration of monosaccharides were investigated by using two commercial nanofiltraton (NF) membranes with synthetic glucose-xylose-furfural solution as model. The effects of main operating parameters such as feed pH, permeation flux, temperature and feed concentration on the rejections of the three solutes, were studied. Results showed that rejections of the three solutes decreased with increasing feed pH and temperature, and increased with increasing permeation flux for both membranes. The concentrations of the three solutes had interaction effect on the rejection of furfural by NF90 membrane and rejections of the three solutes by NF270 membrane. Furthermore, the effects of two filtration modes, concentration and diafiltration, on the separation of furfural from monosaccharides were also investigated. With the two commercial NF membranes, concentration and purification of monosaccharides in the model solution can be accomplished.
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Affiliation(s)
- Benkun Qi
- National Key Laboratory of Biochemical Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China
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