Industrial xylanolytic yeast for lignocellulosic bioethanol production
MoRE2020 Fellow Iván Francisco Ciklic, incoming mobility from INTA EEA Mendoza, Argentina, to Chalmers University of Technology
A future biobased society relies on an efficient utilization of renewable raw materials for production of fuels, chemicals and materials. In this project, an experienced researcher from INTA EEA Mendoza, Argentina will come to Chalmers University of Technology to conduct research in the fields of sustainable production of energy and green chemistry, developing yeast strains for production of 2nd generation, lignocellulosic bioethanol.
Xylan is the second to cellulose most common polysaccharide in nature and can comprise up to 35% of the total dry weight of plants. Xylan is however still an underutilized resource, and it is of utmost importance that we learn to make use of all sugars in lignocellulose to create economically feasible processes. The project aim is to develop industrial yeast strains that can break down and ferment xylan to ethanol. Genes encoding enzymes that can degrade xylan will be taken from other microorganisms and inserted into the yeast genome using the state-of-the-art technique “CRISPR/Cas9”. The strains produced will be able to ferment mildly pretreated lignocellulosic hydrolysates with considerably improved production yields compared to the starting strain.
Two leading companies for yeast strain development and ethanol production act as project end-users; Gothenburg-based Taurus Energy AB and Argentinean Porta Hnos A.S., providing expertise and new perspectives on research utilization and industrial fermentations. This mobility grant will enable a long sought-after collaboration between both academic and private sectors in VGR and abroad. The knowledge exchange and generation of industrially tractable yeast strains will be highly beneficial to all partners as well as project stakeholders including biotech companies and the scientific community.
Collaborating end-users: Taurus Energy AB and Porta Hnos A.S.
Summary of Project Results
In our project at Chalmers we are conducting research in the fields of sustainable production of energy and green chemistry to contribute for a reduction in our dependence on fossil resources. In such a bio-based economy, plant biomass, or lignocellulose, is an important starting material for production of fuels, chemicals and materials. The energy in lignocellulose is stored in three different carbon polymers, cellulose, hemicellulose and lignin. Hemicellulose is mainly composed of xylan, a polymer of xylose which can comprise up to 35% of the total dry weight of plants. During bioethanol production, xylan is converted to xylose primarily through the biomass pretreatment step. Unfortunately, during this process also various inhibitory compounds are formed that are detrimental for subsequent enzymatic hydrolysis and fermenting yeasts. Mild pretreatment conditions result in a reduced inhibitory burden but also in an incomplete breakdown of xylan polymers. Thus, the overall aim of our work has been to construct an industrial yeast that can efficiently degrade and ferment xylan. If we could tailor our xylose-fermenting S. cerevisiae strain (provided by the end-user Taurus Energy AB) to efficiently degrade xylan, milder pretreatments could be used leading to higher productivity and cost effectiveness of lignocellulosic bioethanol production. For this purpose, we have tested different signal-peptides to optimize secretion of two major xylanolytic enzymes. Our results suggest that secretion can be improved by using these alternative signals. The integration of multiple copies of the best performing signal-peptide/enzyme combination will be possible with our novel CRISPR/Cas9-based method. This method also allows the fine-tuning of integrated gene copy number to achieve ideal gene expression levels and further improve the xylanolytic capacity of our yeast strain.