Institute for Biotechnology and Bioengineering, Centre of Genomics and Biotechnology, (IBB/CGB-UTAD), University of Tras-os-Montes and Alto Douro, School of Life Sciences and Environment, Vila Real, Portugal.
J Microbiol Biotechnol. 2010 Sep;20(9):1314-21. doi: 10.4014/jmb.1003.03039.
Sulfur metabolism in S. cerevisiae is well established, but the mechanisms underlying the formation of sulfide remain obscure. Here we investigated by real time RT-PCR the dependence of expression levels of MET3, MET5/ECM17, MET10, MET16 and MET17 along with SSU1 on nitrogen availability in two wine yeast strains that produce divergent sulfide profiles. MET3 was the most highly expressed of the genes studied in strain PYCC4072, and SSU1 in strain UCD522. Strains behaved differently according to the sampling times, with UCD522 and PYCC4072 showing the highest expression levels at 120h and 72h, respectively. In the presence of 267mg assimilable N/l, the genes were more highly expressed in strain UCD522 than in PYCC4072. MET5/ECM17 and MET17 were only weakly expressed in both strains under any condition tested. MET10 and SSU1 in both strains, but MET16 only in PYCC4072, were consistently up-regulated when sulfide production was inhibited. This study illustrates that strain genotype could be important in determining enzyme activities and therefore the rate of sulfide liberation. This linkage, for some yeast strains, of sulfide production to expression levels of genes associated to sulfate assimilation and sulfur amino acid biosynthesis could be relevant for defining new strategies for genetic improvement of wine yeasts.
酵母细胞中的硫代谢过程已得到充分研究，但硫化物形成的机制仍不清楚。本研究通过实时 RT-PCR 分析了在两种产生不同硫化物谱的葡萄酒酵母菌株中，随着氮源可用性的变化，MET3、MET5/ECM17、MET10、MET16 和 MET17 以及 SSU1 表达水平的变化。在 PYCC4072 菌株中，MET3 是研究的基因中表达水平最高的基因，而在 UCD522 菌株中则是 SSU1。根据采样时间，菌株表现出不同的行为，UCD522 和 PYCC4072 分别在 120h 和 72h 时表现出最高的表达水平。在 267mg 可同化氮/升的存在下，UCD522 菌株中的基因表达水平高于 PYCC4072 菌株。在任何测试条件下，MET5/ECM17 和 MET17 在两个菌株中均表达较弱。在两个菌株中，MET10 和 SSU1，但仅在 PYCC4072 菌株中，MET16 被一致上调，当硫化物产生受到抑制时。本研究表明，菌株基因型可能对酶活性，进而对硫化物释放速度具有重要影响。对于某些酵母菌株，硫化物产生与硫酸盐同化和含硫氨基酸生物合成相关基因表达水平之间的这种联系，可能与定义葡萄酒酵母遗传改良的新策略有关。
