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PGASO: A synthetic biology tool for engineering a cellulolytic yeast

Jui-Jen Chang12, Cheng-Yu Ho34, Feng-Ju Ho1, Tsung-Yu Tsai1, Huei-Mien Ke15, Christine H-T Wang1, Hsin-Liang Chen1, Ming-Che Shih6*, Chieh-Chen Huang34* and Wen-Hsiung Li127*

Author Affiliations

1 Biodiversity Research Center, Academia Sinica, Taipei, 115, Taiwan

2 Genomics Research Center, Academia Sinica, Taipei, 115, Taiwan

3 Department of Life Sciences, National Chung Hsing University, Taichung, 402, Taiwan

4 Biotechnology Center, National Chung Hsing University, Taichung, 115, Taiwan

5 Microbial Genomics, National Chung Hsing University, Taichung, 402, Taiwan

6 Agricultural Biotechnology Research Center, Academia Sinica, Taipei, 115, Taiwan

7 Department of Ecology and Evolution, University of Chicago, Chicago, IL, 60637, USA

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Biotechnology for Biofuels 2012, 5:53  doi:10.1186/1754-6834-5-53

Published: 27 July 2012



To achieve an economical cellulosic ethanol production, a host that can do both cellulosic saccharification and ethanol fermentation is desirable. However, to engineer a non-cellulolytic yeast to be such a host requires synthetic biology techniques to transform multiple enzyme genes into its genome.


A technique, named Promoter-based Gene Assembly and Simultaneous Overexpression (PGASO), that employs overlapping oligonucleotides for recombinatorial assembly of gene cassettes with individual promoters, was developed. PGASO was applied to engineer Kluyveromycesmarxianus KY3, which is a thermo- and toxin-tolerant yeast. We obtained a recombinant strain, called KR5, that is capable of simultaneously expressing exoglucanase and endoglucanase (both of Trichodermareesei), a beta-glucosidase (from a cow rumen fungus), a neomycin phosphotransferase, and a green fluorescent protein. High transformation efficiency and accuracy were achieved as ~63% of the transformants was confirmed to be correct. KR5 can utilize beta-glycan, cellobiose or CMC as the sole carbon source for growth and can directly convert cellobiose and beta-glycan to ethanol.


This study provides the first example of multi-gene assembly in a single step in a yeast species other than Saccharomyces cerevisiae. We successfully engineered a yeast host with a five-gene cassette assembly and the new host is capable of co-expressing three types of cellulase genes. Our study shows that PGASO is an efficient tool for simultaneous expression of multiple enzymes in the kefir yeast KY3 and that KY3 can serve as a host for developing synthetic biology tools.

Consolidated bioprocess; Synthetic biology; Yeast; Cellulolytic enzymes; Bio-ethanol