ABSTRACT
The purpose of this investigation is to improve ethanol production and decrease acetate formation in Saccharomyces cerevisiae strain YS2-?adh2.The strain YS2-?adh2 with deleted alcohol dehydrogenase Ⅱ(adh2) gene was isolated in our lab with higher ethanol production than that of the strain YS2.The ace-taldehyde dehydrogenase Ⅵ(ald6) gene encoded a cytosolic acetaldehyde dehydrogenase,a key enzyme of the pyruvate dehydrogenase(PDH) bypass,transfers acetaldehyde to acetate.To disrupt ald6 gene of the strain YS2-?adh2,ald6 gene targeting cassettes were synthesized by long flanking homology PCR(LFH-PCR) and then were transformed into YS2-?adh2 mutants by LiAc/SS Carrier DNA/PEG method.Positive transformants were selected with G418 and further confirmed by PCR.Once correctly integrated into the genome,the selective marker was rescued by transforming the plasmid pSH65 into the positive transformants and inducing the Cre expression with a Cre/loxP-mediated marker removal procedure.We named the ald6 gene knocked-out strain as YS2-?adh2-?ald6 which has a 12.5% higher ethanol production and a 18% lower acetate formation compared to the strain YS2.
ABSTRACT
The sfa1 gene encoded a bifunctional enzyme with the activities of both alcohol dehydrogenase and glutathione-dependent formaldehyde dehydrogenase in Saccharomyces cerevisiae.The gene disruption cassette produced by PCR using the same long oligonucleotides which comprise 19 or 22 nucleotides complementary to sequences in the templates(pUG6 and pUG66 marker plasmid)at 3' end and 45 nucleotides at 5' end that annealed to sites upstream or downstream of the genomic target sequence to be deleted.After two linear disruption cassettes with a Cre/loxP mediated marker were transformed into the cells of Saccharomyces cerevisiae YS-1,the positive transformants were checked by PCR to correct the integration of the cassette and concurrent deletion of the chromosomal target sequence.Once correctly integrated into the genome,the select marker can be efficiently rescued by transformating the plasmid pSH47 into YS-1 and inducing the Cre expression with a Cre/loxP-mediated marker removal procedure.The expression of the Cre recombinase finally resulted in the removal of the marker gene,leaving behind a single loxP site at the chromosomal locus.The diploid mutant YS-1-sfa1 was generated,which could enhance the output of ethanol with 8.0% by shaking culture in flask compared with the original strain YS-1.