中文摘要：

诱变筛选发酵玉米芯水解液高产苹果酸的根霉属菌株,并对其进行代谢分析,研究其高产苹果酸的机理。对分离得到的菌株进行ITS序列鉴定,进一步利用软X射线辐射对菌种进行诱变筛选、对出发菌株和突变菌株的相关酶活力进行测定及代谢通量分析。利用软X射线辐射结合丙烯醇平板筛选乙醇脱氢酶缺陷型菌株,得到突变株-1,发现其乙醇脱氢酶基因的3处密码子突变为＂TAA＂,阻断了突变菌株的乙醇代谢途径。进而利用软X射线辐射结合氟乙酸平板筛选乙醛酸循环缺陷型菌株,得到复合突变株-2,降低了副产物富马酸及琥珀酸的产量。复合突变株-2的葡萄糖-6-磷酸脱氢酶中几处NADP（H）结合位点发生突变,增加了糖酵解和磷酸戊糖两种途径的相互作用,促进了其戊糖代谢。经过两步分离筛选,得到的复合突变株-2能发酵玉米芯水解液高产苹果酸,且减少了副产物乙醇、富马酸、琥珀酸的生成。复合突变株-2的苹果酸产量占代谢物总产量的比例由出发菌株的71%增加到91%,苹果酸产量增大1倍,研究成果对工业化利用突变菌株生产苹果酸具有重要意义。

英文摘要：

High-level production of malic acid by fermentation of com cob hydrolysate with an isolated Rhizopus delemar strain was expected. Then metabolic analysis and research of the underlying mechanism were carried out. Phylogenetic analysis based on ITS region sequences was carded out for the identification of X-ray-induced mutant strains, and the key enzyme activities and metabolic flux were also analyzed. The results showed 3 ＂TAA＂ codons in the alcohol dehydrogenase gene of the anti-allyl mutant strain, which interrupt the pathway of ethanol metabolism. The breeding for the anti- fluoroacetate mutant strain succeeded to decrease the flux of fumaric and succinic acid. Some NADP （H）-binding loci were mutated in the G6PDH gene of the mutant, probably leading to increased interaction of Embden-Meyerhof-Parnas pathway with Hexose-Monophophate pathway and improved pentose metabolism. After two-step breeding and regulation for this isolated strain, the production of malic acid was enhanced markedly; the formation of ethanol, fumaric acid and succinic acid were decreased simultaneously. Compared with the parent strain, the proportion of malic acid in mutant strain-2 increased to 91% from 71% and the yield of malic acid was increased markedly, which is of significance for deep industrial development.