Reduction of methionine based sulfur-containing carcinogen using halotolerant yeast cells

J.H.Weisburger等人^ <1）>从日本加工的海产品--盐渍的秋刀鱼中分离出能够诱导胃癌的化合物2-氯-4-甲硫基丁酸（CMBA）。CMBA是在蛋氨酸、亚硝酸钠和氯化钠的存在下产生的，这些物质被用作食品添加剂。在这项研究中，我们试图使用从豆瓣酱中分离的耐盐酵母来减少CMBA的产生量。为了分析CMBA的量，我们使用鼠伤寒沙门氏菌TA 100、沙门氏菌的组氨酸营养缺陷型突变体或艾姆斯试验进行了致突变性试验。回复突变菌落数随鲁氏接合酵母S-2B（耐盐酵母）浓缩提取物的加入量而减少，当将30μl浓缩提取物（相当于1.2× 10^7个细菌）加入50 gg CMBA中时，观察到回复突变菌落数减少约30%。使用耐盐酵母鲁氏接合酵母S96和非耐盐酵母清酒酵母的酿酒酵母RIB 6002（Kyokai No.7）作为试验菌株。将两株菌分别用CMBA培养0、0.5、3和24 h。结果，发现两种菌株都随着接触时间的增加而减少培养物中存在的CMBA的量。在24 h的接触时间后，鲁氏发酵单胞菌S96和酿酒酵母在24 h的接触时间后的减少率分别为29.7%和14.2%。这种减少可能是因为发现CMBA吸附在带正电荷的酵母细胞表面上。基于这些结果，我们得出结论，CMBA，这是已知的导致胃癌，可以有效地减少使用耐盐酵母细胞。等人：《自然》，374，599（1995）

J.H.Weisburger, et al.^<1)> isolated a compound, 2-chloro-4-methylthiobutanoic acid (CMBA), capable of inducing gastric cancer from a salted Pacific saury, which is a Japanese processed marine product. CMBA is produced in the presence of methionine, sodium nitrite and sodium chloride, which are used as food additives.In this study, we attempted to reduce the amount of CMBA produced using a halotolerant yeast isolated from a soybean paste. For analyzing the amount of CMBA, we performed a mutagenicity test using Salmonella tryphimurium TA100, histidine auxotrophic mutant of Salmonella or Ames test. The number of reverse mutation colonies decreased depending on the amount of concentrated extract of Zygosaccharomyces rouxii S-2B (halotolerant yeast) was added, and about 30% reduction was observed when 30μl (equivalent to〜1.2×10^7bacteria) of the concentrated extract was added to 50 gg of CMBA.In addition, the inhibitory effects of the yeast cells toward CMBA were determined by culturing. Zygosaccharomyces rouxii S96, a halotolerant yeast, and Saccharomyces cerevisiae RIB6002 (Kyokai No.7) of sake yeast, a non-halotolerant yeast, were used as test strains. Both the strains were cultured with CMBA for 0, 0.5, 3, and 24h. As a result, both strains were found to decrease the amount of CMBA present in the culture with increase in contact time. The reduction rates after 24 h of contact time were 29.7% for Z.rouxii S96 and 14.2% for S.cerevisiae in 24h of contact time. This reduction was probably because CMBA was found to be adsorbed on the positively charged surface of yeast cells. Based on these results, we conclude that CMBA, which is known to cause gastric cancer, can effectively be reduced using halotolerant yeast cells.1) Wei Chen, John H.Weisburger, et. al. : NATURE, 374, 599 (1995)