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

J.H.Weisburger等人[1]从一种日本加工海产品——太平洋盐鲜鱼中分离出一种能诱发胃癌的化合物——2-氯-4-甲基硫代丁酸（CMBA）。CMBA是在蛋氨酸、亚硝酸钠和氯化钠存在的情况下生产的，这些物质被用作食品添加剂。在这项研究中，我们试图使用从大豆酱中分离出的耐盐酵母来减少CMBA的产量。为了分析CMBA的含量，我们采用了斑疹伤寒沙门氏菌TA100、组氨酸营养不良沙门氏菌突变体或Ames试验进行了诱变性试验。随着Zygosaccharomyces rouxii S-2B（耐盐酵母）浓缩提取物的添加量的增加，反突变菌落的数量减少，当30μl（相当于~ 1.2×10^7个细菌）的浓缩提取物加入50 gg CMBA时，反突变菌落的数量减少约30%。此外，通过培养测定了酵母细胞对CMBA的抑制作用。以耐盐酵母Zygosaccharomyces rouxii S96和不耐盐的清酒酵母Saccharomyces cerevisiae RIB6002 （Kyokai No.7）为试验菌株。两株菌株分别用CMBA培养0、0.5、3和24h。结果发现，随着接触时间的增加，这两种菌株在培养物中存在的CMBA量都减少了。接触24h后，rouxii S96的还原率为29.7%，cerevisiae的还原率为14.2%。这种减少可能是因为发现CMBA被吸附在酵母细胞的正电荷表面。基于这些结果，我们得出结论，已知会导致胃癌的CMBA可以使用耐盐酵母细胞有效地减少。1)陈伟，John H.Weisburger等，《自然》杂志，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)