Microbial Biodegradation of Lignocellulose for Ethanol Production

Altun, Burçin (2015). Microbial Biodegradation of Lignocellulose for Ethanol Production. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.0000efb4

Abstract

Bioethanol can be produced from a range of substrates and it is considered to be renewable. Lignocellulose is one of the substrates that can be used for bioethanol production. Genetic engineering of a microorganism that can completely convert all the sugars of cellulosic material into ethanol is one of the important steps for the production process.

This study has two parts that aim to produce bioethanol by using genetically modified microorganisms. The first part of the study deals with bioethanol production from lignocellulosic material by microbial fermentation in two steps. The first step is the degradation of the lignocellulosic material by Bacilli to produce cellobiose, and the second step is to convert cellobiose into glucose by a B-glucosidase expressing recombinant yeast strain. As lignocellulosic material, wood powder from industrial waste was used and the degradation of the wood powder into glucose was confirmed by following the growth curve of the microorganisms and through appropriate enzymatic assays.

The second part of the study utilizes two novel technologies, Yeast Artificial Chromosome (YAC) and Bridge-Induced Translocation (BIT) to introduce new, multi-factorial genetic traits into a yeast strain, a process that would otherwise take several time-consuming and labor-intensive rounds of genetic engineering. After cloning exogenous cellulases onto a YAC vector, this was transformed into a PEP4 mutant yeast upon which BIT technology was applied. This technology allowed the research to gain two advantages; one of them was to stabilize the YAC within the yeast genome and the other one was to have increased gene expression level consequent to the translocation event.

In conclusion, this work defines a successful microbial system that is able to efficiently utilize lignocellulosic material as a carbon source and a translocant yeast strain that has high level of cellulase activity.