| Molybdenum is one of essential trace element of animals and human beings. It is the most important part of enzymes, such as nitrogenase, nitrate reductase, xanthine oxidase and sulfite oxidase. It influences and participates in many metabolisms of body, such as electron transfer of cell, iron metabolism and oxidation of aldehyde, etc. Molybdenum plays a good role in preventing and treating cancer, liver diseases, cardio-/cerebrovascular disease, Keshan disease, decayed tooth, hypochromic microcytic anemia and regional alopecia, etc.Molybdenum-enriched yeast is non-toxic and has high combinability and absorptivity. So, as a complementarity of organic-molybdenum and an important component of the medicament to prevent and treat the diseases as above, molybdenum-rich yeast has attracted huge attentions. Our purpose of this research was to breed new strains of Saccharomyces cerevisiae having higher molybdenum enrichment abilities by multi-mutagenesis breeding with ultraviolet and microwave, assaying their biological functions and the activities of nitrate reductase and xanthine oxidase and applying them to production.After the original strain Saccharomyces cerevisiae Y1 whose resistance level to Na2MoO4 was 20mmol/L was selected from 10 strains (Y1, Y19, Y21, Y22, Y23, Y24, Y26, Y27, Y30 and Y31) , Y1 was haploided. The resistance levels of its haploids as well as SY10, SY11, SY12 and SY14 were determined to select the higher resistant strain. A strain named SY10 whose resistant level is the highest, reached to 70mmol/L.Then SY10 was lysised to get rid of cell wall by snailase. SY10 and the protoplasts obtained were mutated with ultraviolet ray. When the irradiation times were 3 min and 4 min, respectively, the highest positive mutate ratios were obtained. After tolerance assay to Na2MoO4 in liquid, mutant strains named SY10-186p and SY10-150s whose Mo6+ resistant level were 300 mmol/L and 350 mmol/L were selected, respectively. The Mo6+ resistant level of them were 4.29 and 5.0 folds higher than thatn of the original strain SY10. Then the protoplasts of mutated strain SY10-186p and the haploid of mutated strain SY10-150s were mutated with ultraviolet ray again by the same method above. When the irradiation times were 4min and 6 min, respectively, the highest positive mutate ratios were obtained. After tolerance assay to Na2MoO4 in liquid, mutant strains named SY10-186p-216u and SY10-150s-208u whose Mo6+ resistance level were both 400 mmol/L (5.71 folds higher than the original strain) were selected, respectively, and their biomasses reached to 4.575 g/L and1.610 g/L,which were 1.75 and 1.94 folds higher than that of the original strain, respectively. Total molybdenum ions accumulated in the cells were estimated by atomic absorption spectrophotometer, which were 38.52mg/L and 43.95 mg/L, were 4.86 and 5.55 folds higher than the original strain, respectively. Organic-molybdenum accumulated in the cells were estimated by ICP-AES, which were 15.87 mg/L and 14.20 mg/L, were 31.74 and 28.40 folds higher than the original strain, respectively.Then the protoplasts of mutated strain SY10-186p and the haploid of mutated strain SY10-150s were mutated with microwave in a microwave oven (2450 MHz, 850 W), and the optimum irradiation times were both 5 s. After tolerance assay to Na2MoO4 in liquid, mutant strains named SY10-186p-8m and SY10-150s-48m whose Mo6+ resistant level were both 400 mmol/L (5.71 folds higher than the original strain) were selected, and their biomasses reached to 3.725 g/L and 2.210 g/L,which were 1.42 and 2.26 folds higher than the original strain, respectively. Total copper ions accumulated in the cells were estimated by atomic absorption spectrophotometer, which were 39.13 mg/L and 40.05 mg/L, were 4.94 and 5.06 folds higher than the original strain, respectively. Organic-molybdenum accumulated in the cells were estimated by ICP-AES, which were 15.08 mg/L and 17.24 mg/L, were 30.16 and 34.48 folds higher than that of the original strain, respectively.We also assayed the activities of xanthine oxidase and nitrate reductase of the four mutant strains, and the activities of them were higher in comparison with those of initial strain which were 7.679 U/L, 7.380 U/L, 7.679 U/L, 8.876 U/L and 0.784 U/L, 1.040 U/L, 0.525 U/L, 0.691U/L, about 15.42, 14.82, 15.42, 17.82-fold and 2.12, 2.81, 1.42, 1.87-fold higher than that of the original strain, respectively.For all the measured generations, genetic stability of SY10-186p-216u, SY10-150s-208u, SY10-186p-8m and SY10-150s-48m all maintained above 90%, suggesting that the mutant strains were genetically stable after 50 generations.The capacities of resisting UV, clearing ?OH and O2-? free radical were also compared to that of the original strain. The results showed that lethality of the mutants to UV reduced obviously and the capacities of SY10-186p-216u,SY10-150s-208u,SY10-186p-8m and SY10-150s-48m in clearing ?OH and O2-? free radical which were 67.26 %, 73.08 %, 76.55 %, 62.66 % and 39.8 %, 41.1 %, 40.5 %, 43.9 %, were 7.22, 5.91, 6.34, 6.89-fold and 3.09, 3.26, 3.21, 3.48-fold higher than the original strain, respectively.
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