PDF(Pubmed)
Abstract：
The genetic stability and metabolic robustness of production strains is one of the key criteria for the production of bio-based products by microbial fermentation on an industrial scale. These criteria were here explored in an industrial ethanol-producer strain of Saccharomyces cerevisiae able to co-ferment D-xylose and L-arabinose with glucose through the chromosomal integration of several copies of pivotal genes for the use of these pentose (C5) sugars. Using batch sequential cultures in a controlled bioreactor that mimics long-term fermentation in an industrial setting, this strain was found to exhibit significant fluctuations in D-xylose and L-arabinose consumption as early as the 50th generation and beyond. These fluctuations seem not related to the few low-consumption C5 sugar clones that appeared throughout the sequential batch cultures at a frequency lower than 1.5% and that were due to the reduction in the number of copies of transgenes coding for C5 sugar assimilation enzymes. Also, subpopulations enriched with low or high RAD52 expression, whose expression level was reported to be proportional to homologous recombination rate did not exhibit defect in C5-sugar assimilation, arguing that other mechanisms may be responsible for copy number variation of transgenes. Overall, this work highlighted the existence of genetic and metabolic instabilities in an industrial yeast which, although modest in our conditions, could be more deleterious in harsher industrial conditions, leading to reduced production performance.
摘要：
生产菌株的遗传稳定性和代谢稳健性是通过工业规模的微生物发酵生产生物基产品的关键标准之一。这些标准是在酿酒酵母的工业乙醇生产菌株中探索的，该菌株能够通过使用这些戊糖（C5）糖的关键基因的几个拷贝的染色体整合，将D-木糖和L-阿拉伯糖与葡萄糖共发酵。在受控生物反应器中使用分批顺序培养，模拟工业环境中的长期发酵，早在第50代及以后，就发现该菌株在D-木糖和L-阿拉伯糖的消耗中表现出明显的波动。这些波动似乎与在整个连续分批培养中以低于1.5％的频率出现的少数低消耗C5糖克隆无关，这是由于编码C5糖同化酶的转基因拷贝数减少所致。此外，富含低或高RAD52表达的亚群，据报道，其表达水平与同源重组率成比例，在C5糖同化中没有表现出缺陷，认为其他机制可能是导致转基因拷贝数变异的原因。总的来说,这项工作强调了工业酵母中遗传和代谢不稳定性的存在，虽然在我们的条件下适度，在更恶劣的工业条件下可能更有害，导致生产性能下降。
