Pretreatment of lignocellulose yields a complex sugar mixture that potentially can be converted into bioethanol and other chemicals by engineered yeast. One approach to overcome competition between sugars for uptake and metabolism is the use of a consortium of specialist strains capable of efficient conversion of single sugars. Here we show that maltose inhibits cell growth of a xylose-fermenting specialist strain IMX730.1 that is unable to utilize glucose because of the deletion of all hexokinase genes. The growth inhibition cannot be attributed to a competition between maltose and xylose for uptake. The inhibition is enhanced in a strain lacking maltase enzymes (dMalX2) and completely eliminated when all maltose transporters are deleted. High-level accumulation of maltose in the dMalX2 strain is accompanied by a hypotonic-like transcriptional response, while cells are rescued from maltose-induced cell death by the inclusion of an extracellular osmolyte such as sorbitol. These data suggest that maltose-induced cell death is due to high levels of maltose uptake causing hypotonic-like stress conditions and can be prevented through engineering of the maltose transporters. Transporter engineering should be included in the development of stable microbial consortia for the efficient conversion of lignocellulosic feedstocks.

中文翻译：

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麦芽糖积累诱导酿酒酵母细胞死亡

木质纤维素的预处理产生复杂的糖混合物，可以通过工程酵母将其转化为生物乙醇和其他化学品。克服糖之间的吸收和代谢竞争的一种方法是使用能够有效转化单糖的专业菌株联盟。在这里，我们发现麦芽糖抑制木糖发酵专用菌株 IMX730.1 的细胞生长，该菌株由于删除了所有己糖激酶基因而无法利用葡萄糖。生长抑制不能归因于麦芽糖和木糖之间的吸收竞争。在缺乏麦芽糖酶 (dMalX2) 的菌株中，抑制作用增强，而当删除所有麦芽糖转运蛋白时，抑制作用完全消除。 dMalX2 菌株中麦芽糖的高水平积累伴随着低渗样转录反应，而通过加入细胞外渗透剂（如山梨醇），可以将细胞从麦芽糖诱导的细胞死亡中拯救出来。这些数据表明，麦芽糖诱导的细胞死亡是由于高水平的麦芽糖摄取导致低渗样应激条件，并且可以通过麦芽糖转运蛋白的改造来预防。转运蛋白工程应纳入稳定微生物群落的开发中，以实现木质纤维素原料的有效转化。