School of Microbiology, University College Cork, Cork T12YN60, Ireland.
Institute of Molecular Biosciences, Goethe University Frankfurt, 60438 Frankfurt am Main, Germany.
FEMS Yeast Res. 2017 May 1;17(3). doi: 10.1093/femsyr/fox021.
Kluyveromyces marxianus is a safe yeast used in the food and biotechnology sectors. One of the important traits that sets it apart from the familiar yeasts, Saccharomyces cerevisiae, is its capacity to grow using lactose as a carbon source. Like in its close relative, Kluyveromyces lactis, this requires lactose transport via a permease and intracellular hydrolysis of the disaccharide. Given the importance of the trait, it was intriguing that most, but not all, strains of K. marxianus are reported to consume lactose efficiently. In this study, primarily through heterologous expression in S. cerevisiae and K. marxianus, it was established that a single gene, LAC12, is responsible for lactose uptake in K. marxianus. Strains that failed to transport lactose showed variation in 13 amino acids in the Lac12p protein, rendering the protein non-functional for lactose transport. Genome analysis showed that the LAC12 gene is present in four copies in the subtelomeric regions of three different chromosomes but only the ancestral LAC12 gene encodes a functional lactose transporter. Other copies of LAC12 may be non-functional or have alternative substrates. The analysis raises some interesting questions regarding the evolution of sugar transporters in K. marxianus.
马克斯克鲁维酵母是一种安全的酵母，用于食品和生物技术领域。它与常见的酵母——酿酒酵母不同，一个重要的特点是能够利用乳糖作为碳源进行生长。就像在其近亲克鲁维酵母中一样，这需要通过渗透酶进行乳糖运输，并在细胞内水解二糖。鉴于该特性的重要性，令人感到好奇的是，大多数但不是所有的马克斯克鲁维酵母菌株都被报道能够有效地消耗乳糖。在这项研究中，主要通过在酿酒酵母和马克斯克鲁维酵母中的异源表达，确定了一个单一的基因 LAC12 负责马克斯克鲁维酵母中的乳糖摄取。不能运输乳糖的菌株在 Lac12p 蛋白中有 13 个氨基酸的变异，使该蛋白无法进行乳糖运输。基因组分析表明，LAC12 基因存在于三个不同染色体的端粒区域的四个拷贝中，但只有原始的 LAC12 基因编码功能性的乳糖转运蛋白。其他 LAC12 拷贝可能是无功能的或具有替代底物。该分析提出了一些关于马克斯克鲁维酵母中糖转运蛋白进化的有趣问题。
