Construction Of High-temperature Tolerant Yeast By Genome Shuffling

Soy sauce and soybean paste has become an important condiment in our country. The main production process of soy sauce includes low salt solid state fermentation technology and high salt liquid state fermentation technology. The low salt solid state fermentation technology has the advantages of simple equipment, short fermentation time and low cost.However, because of the highfermentation temperature, the salt tolerant yeast growth is limited, leading to lowqualityof the product which only reach the national standard level three and in color and flavor are not as good as that produced from high salt liquid state fermentation. At the same time, there are similar problems in soybean paste. Therefore,using genome shuffling S yeast and T yeast usually added in the high salt liquid state soy were constructed for growth under high temperature condition, which can be applied to the low salt solid state soy sauce fermentation and soybean paste fermentation to produce the higher quality condiment.It was found that the optimum growth temperature of S yeast and T yeast was 25℃ to 30℃, and the maximum tolerance temperature was 36℃ in solid medium. Using ultraviolet light(UV) and ethyl methyl sulfonate (EMS) S yeast and T yeast were mutated, respectively,and two rounds of genome shuffling were carried out.Finally,the new strains were constructed, which could grow under42℃, and were named S1, S2, T1 and T2, respectively.The genetic characters of the newly constructed four strains were stable.The morphology of S1 yeast and S2 yeast cells was longer than that of the original strain S yeast, and the morphology of T1 yeast and T2 yeast cells had no significant changescompared with the original strain T yeast. The contents of DNA in four new yeast cells were changed compared with the control strain, showing that maybe there was a genome rearrangement in the yeast cell.The newly constructed four strains and the starting strain S yeast and T yeast were used in soybean paste fermentation, and the physical and chemical indexes were detected during the fermentation process. The results showed that the content of amino acid nitrogen in soybean paste added with S2 yeast reached 1.02g/100g, and 41 kinds of flavor compounds were found. The content of amino acid nitrogen in soybean paste with T2 yeast was 1.03g/100g, and 40 kinds of flavor compounds were detected.The newly constructed four strains and the starting strain S yeast and T yeast were used in the low salt solid state soy sauce fermentation, and the physical and chemical indexes were detected during the fermentation process. The results showed that the content of amino acid nitrogen in soybean paste added with S2 yeast reached 1.06g/100mL, and 53 kinds of flavor compounds were found. The content of amino acid nitrogen in soybean paste with T2 yeast was 1.04g/100mL, and 56 kinds of flavor compounds were detected.