酪丁酸梭菌代谢工程菌的构建及其发酵特性

Engineering and metabolic characteristics of a Clostridium tyrobutyricum strain

摘要:

酪丁酸梭菌Clostridium tyrobutyricum可以利用葡萄糖、木糖、纤维二糖、阿拉伯糖等多种底物进行产酸发酵，主要发酵产物为丁酸和乙酸，是一种适合于木质纤维素同步糖化发酵生产丁酸的菌种。将酪丁酸梭菌乙酸发酵关键基因取代为丁酸发酵关键基因来构建突变株，可使突变株丁酸发酵量增多，乙酸发酵量减少。分别获得来源于丙酮丁醇梭菌的丁酸代谢关键酶基因——乙酰乙酰辅酶A转移酶基因 (thl)、来源于酪丁酸梭菌本身的乙酸代谢关键酶基因片段——磷酸转乙酰基酶基因片段 (pta) 和来源于质粒pIMP1的红霉素抗性基因 (em)。将它们与质粒pUC19相连构建为非复制性质粒pUC19-EPT。通过电转化将其导入酪丁酸梭菌中。利用红霉素抗性平板筛选获得转化子，通过PCR验证发现，获得的突变株染色体上pta被thl替换。在以葡萄糖为底物的发酵中，突变株丁酸得率为0.47，较野生型增大了34％，乙酸得率为0.05，较野生型下降了29％。

Abstract:

Clostridium tyrobutyricum is suitable for simultaneous saccharification and fermentation of lignocellulosic. It can produce butyric acid, acetic acid as its main fermentation products from a wide variety of carbohydrates such as glucose, xylose, cellobiose and arabinose. In order to decrease acetic acid content and increase butyric acid content in C. tyrobutyricum, we replaced genes on the acetic acid fermentation pathway with genes on the butyric acid fermentation pathway. Three genes were selected. They were acetyl-CoA acetylrtansfers gene (thl) which is the key enzyme gene associated with acetic acid fermentation pathway from Clostridium acetobutylicum, erythromycin gene (em) from plasmid pIMP1 and phosphotransacetylase gene (pta) which is the key enzyme gene associated with butyric acid fermentation pathway from C. tyrobutyricum. We fused these genes with pUC19 to construct nonreplicative integrated plasmids pUC19-EPT. Then we transformed pUC19-EPT into C. tyrobutyricum through electroporation. The recombinant transformants grown on plates containing erythromycin were validated by PCR. A mutant whose pta gene was displaced by thl gene on the chromosome was selected. In the fermentation from glucose, the mutant’s yield of butyric acid is 0.47, increased by 34% compared with wild type; and the yield of acetic acid is 0.05, decreased by 29% compared with wild type.