Yarrowia lipolytica is a yeast with many talents, one of them being the production of citric acid. Although the citrate biosynthesis is well studied, little is known about the transport mechanism by which citrate is exported. To gain better insight into this mechanism, we set out to identify a transporter involved in citrate export of Y. lipolytica. A total of five proteins were selected for analysis based on their similarity to a known citrate exporter, but neither a citrate transport activity nor any other phenotypic function could be attributed to them. Differential gene expression analysis of two strains with a distinct citrate productivity revealed another three putative transporters, one of which is YALI0D20196p. Disrupting YALI0D20196g in Y. lipolytica abolished citrate production, while extrachromosomal expression enhanced citrate production 5.2-fold in a low producing wildtype. Furthermore, heterologous expression of YALI0D20196p in the non-citrate secreting yeast Saccharomyces cerevisiae facilitated citrate export. Likewise, expression of YALI0D20196p complemented the ability to secrete citrate in an export-deficient strain of Aspergillus niger, confirming a citrate export function of YALI0D20196p. This report on the identification of the first citrate exporter in Y. lipolytica, termed Cex1, represents a valuable starting point for further investigations of the complex transport processes in yeasts.

中文翻译：

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解脂耶氏酵母柠檬酸盐输出者 Cex1 的鉴定

Yarrowia lipolytica是一种具有多种才能的酵母，其中之一就是生产柠檬酸。尽管柠檬酸盐的生物合成得到了很好的研究，但对柠檬酸盐输出的运输机制知之甚少。为了更好地了解这种机制，我们着手确定参与解脂耶氏酵母输出柠檬酸盐的转运蛋白。根据它们与已知柠檬酸盐输出蛋白的相似性，总共选择了五种蛋白质进行分析，但柠檬酸盐转运活性或任何其他表型功能都不能归因于它们。对具有不同柠檬酸盐生产力的两种菌株的差异基因表达分析揭示了另外三种假定的转运蛋白，其中一种是 YALI0D20196p。破坏解脂耶氏酵母中的YALI0D20196g消除了柠檬酸盐的产生，而染色体外表达使低产量野生型的柠檬酸盐产生增加了 5.2 倍。此外，YALI0D20196p 在非柠檬酸分泌酵母酿酒酵母中的异源表达促进了柠檬酸出口。同样，YALI0D20196p 的表达补充了黑曲霉出口缺陷菌株分泌柠檬酸盐的能力，证实了 YALI0D20196p 的柠檬酸盐出口功能。这份关于鉴定解脂耶氏酵母中第一个柠檬酸盐出口者的报告，称为 Cex1，代表了进一步研究酵母中复杂运输过程的宝贵起点。