Abstract

Bioethanol is gaining increasing attention as a clean and renewable fuel because of its major environmental benefits. Efficient bioethanol fermentation requires the selection of superior strains that are capable of ethanol stress tolerance. Yeast can produce ethanol, thereby reflecting its intrinsic ability to tolerate ethanol. This study focuses on ethanol tolerance enhancement of Saccharomyces cerevisiae for ethanol production improvement through protoplast fusion. S. cerevisiae and P. stipitis fusants (ATCC 58785), which can ferment xylose, were isolated. The ability of these isolates tolerate ethanol was investigated by allowing the strains to grow in different ethanol concentrations. Results showed the ability of the fusantsto have an average tolerance to ethanol when compared with the parent strains and fermented glucose in the presence of 6% ethanol. By contrast, the parent strains S. cerevisiae and P. stipitis showed ethanol tolerances of 8 and 4%, respectively. Fusant formation was confirmed by the increased DNA content. This outcome suggests that multiple fusions had occurred and the genetic stability of fusants indicates that F24 and F18 are genetically stable and suitable for industrial production.

Keywords:

Ethanol tolerant, Pichia stipitis, protoplast fusion, Saccharomyces cerevisiae,

References

1. Ali, M.N. and M.M. Khan, 2014. Screening, identification andcharacterization of alcohol tolerant potential bioethanol producing yeasts. Curr. Res. Microbiol. Biotechnol., 2: 316-24.
   
2. Baeyens, J., K. Qian, A. Lise, D. Raf, L. Yongqin and T. Tianwei, 2015. Challenges and opportunities in improving the production of bio-ethanol. Prog. Energ. Combust., 47: 60-88.
   CrossRef    
3. Dujon, B., D. Sherman, G. Fischer, P. Durrens, S. Casaregola, I. Lafontaine et al., 2004. Genome evolution in yeasts. Nature, 430(6995): 35-44.
   CrossRef    PMid:15229592    
4. GuoLi, G., M. LiYun and C. XueFeng, 2014. Isolation and improvement of Saccharomyces cerevisiae for producing the distilled liquor. J. Chem. Pharmaceut. Res., 6: 283-88.
   
5. Haggran, A.A. and N.A. Abo-Sereih, 2014. Isolation and identification of ethanol tolerant yeast strains. Middle East J. Appl. Sci., 4(3): 600-606.
   
6. Lennartsson, P.R., P. Erlandsson and M.J. Taherzadeh, 2014. Integration of the first and second generation bioethanol processes and the importance of by-products. Bioresour. Technol., 165: 3-8.
   CrossRef    PMid:24582951    
7. Ma, M. and Z.L. Liu. 2010. Mechanisms of ethanol tolerance in Saccharomyces cerevisiae. Appl. Microbiol. Biotechnol., 87: 829-845.
   CrossRef    PMid:20464391    
8. Osho, A., 2005. Ethanol and sugar tolerance of wine yeasts isolated from fermenting cashew apple juice. Afr. J. Biotechnol., 4: 660-662.
   CrossRef    
9. Pérez-Través, L., C.A. Lopes, E. Barrio and A. Querol, 2012. Evaluation of different genetic procedures for the generation of artificial hybrids in Saccharomyces genus for wine making. Int. J. Food Microbiol., 156: 102-111.
   CrossRef    PMid:22503711    
10. Sarkar, N., S.K. Ghosh, S. Bannerjee and K. Aikat, 2012. Bioethanol production from agricultural wastes: An overview. Renew. Energ., 37: 19-27.
    CrossRef    
11. Sevda, S.B. and L. Rodrigues, 2011. Fermentative behavior of saccharomyces strains during guava (Psidium guajava L.) must fermentation and optimization of guava wine production. J. Food Process. Technol., 2: 118.
    
12. Thammasittirong, S.N.R., T. Thirasaktana, A. Thammasittirong and M. Srisodsuk, 2013. Improvement of ethanol production by ethanol-tolerant Saccharomyces cerevisiae UVNR56. Springer Plus, 2: 1-5.
    CrossRef    PMid:25674412 PMCid:PMC4320205    
13. Tikka, C., H.P. Osuru, N. Atluri and P.C.V. Raghavulu, 2013. Isolation and characterization of ethanol tolerant yeast strains. Bioinformation, 9: 421.
    CrossRef    PMid:23750092 PMCid:PMC3670125    
14. Wai, N.K.T, W.N. Nway Oo, M.K. Thu and M. Mya Oo, 2008. Isolation, characterization and screening of thermotolerant, ethanol tolerant indigenous yeasts and study on the effectiveness of immobilized cell for ethanol production. Proceedings of the GMSARN International Conference on Sustainable Development: Issues and Prospects for the GMS.
    
15. Wimalasena, T.T., D. Greetham, M.E. Marvin, G. Liti, Y. Chandelia, A. Hart, E.J. Louis, T.G. Phister, G.A. Tucker and K.A. Smart, 2014. Phenotypic characterisation of Saccharomyces spp. yeast for tolerance to stresses encountered during fermentation of lignocellulosic residues to produce bioethanol. Microb. Cell Fact., 13: 47.
    CrossRef    PMid:24670111 PMCid:PMC3986927    
16. Zhang, M., Y. Xiao, R. Zhu, Q. Zhang and S.L. Wang, 2012. Enhanced thermotolerance and ethanol tolerance in Saccharomyces cerevisiae mutated by high-energy pulse electron beam and protoplast fusion. Bioproc. Biosyst. Eng., 35: 1455-1465.
    CrossRef    PMid:22488242    
17. Zhang, M., R. Zhu, M. Zhang, B. Gao, D. Sun and S. Wang, 2013. High-energy pulse-electron-beam-induced molecular and cellular damage in Saccharomyces cerevisiae. Res. Microbiol., 164: 100-109.
    CrossRef    PMid:23142492    
18. Zhao, X.Q. and F.W. Bai, 2009. Mechanisms of yeast stress tolerance and its manipulation for efficient fuel ethanol production. J. Biotechnol., 144: 23-30.
    CrossRef    PMid:19446584    

Competing interests

The authors have no competing interests.

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