The partial genomic library of Acetobacter suboxydans was constructed using Yeast\| E.coli shuttle plasmid YEp352 as vector.Two positive transformants,designated as DH5α(pAD91) and DH5α(pAD98),were obtained by screening the growth of transformants on the agar plate in which D\|arabitol was used as the sole carbon source.The results of Southern blot and restriction endonuclease analysis showed that the two recombinants are identical.The insert is about 2.3kb.Arabitol dehydrogenase activity assay indicated that the transformants could produce D\|xylulose\|forming D\|arabitol dehydrogenase.Hence,the gene encoding D\|arabitol dehydrogenase exists in the cloned DNA fragment.
Yeast YIp\|type expression recombinant plasmid(pCMA2\|1) was constructed. The expression of α\|acetolactate decarboxylase gene from \%Bacillus subtilis\% was controled by \%CUP1\% promoter and its own terminator. The recombinant plasmid pCMA2\|1 was introduced into the brewer’s yeast PJ3\|5. Transformants were selected using copper resistance as selected marker. The results of activity assay showed that PJ3\|5 didn’t produce α\|acetolactate decarboxylase(ALDC), where as the activity of α\|ALDC in transformants were induced by copper sulfate. The laboratory scale fermentation test confirmed that the total diacetyl concentration was reduced effectively by α\|ALDC in transformant.
The sequence of the flocculation gene (FLO1G) was determined. The result of sequcencing showed that:the cloned gene contains a large open reading frame (ORF) of 3936 bp and encodes for a protein of 1312 amino acid. According to the result of homologous analysis, the cloned gene is homologous to FLO1 but with 675 bp deletion in the ORF region. The missing part belongs to one of the four repeated sequence family of FLO1. Since the cloned DNA fragment can trigger strong flocculence to non-flocculent strain S.cerevisiae YS58, we concluded that the missing part is not the crutical part for the flocculent ability of the gene.
