College of Life Science and Technology, Guangxi University, Nanning, 530004, China.
Appl Biochem Biotechnol. 2014 Jan;172(1):50-61. doi: 10.1007/s12010-013-0421-x. Epub 2013 Sep 18.
Isomaltooligosaccharides (IMO), the glucosylsaccharides used as food additives, are made from saccharified starch by enzymes or microbial cells with transglycosylation activity. This study aimed to generate shuffled futants of Aspergillus niger with enhanced transglycosylation activity for industrial IMO production. The starting mutant population was generated by (60)Co-γ radiation; mutants with higher transglycosylation activity were selected and subjected to recursive protoplast fusion. The resulting fusants were screened by a novel high-throughput method based on detecting non-fermentable reducing sugar. After three rounds of genome shuffling, the best performing strain GS3-3 was obtained, its transglycosylation activity (14.91 U/mL) was increased by 194.1 % compared to that of original strain C-6181. In fermentor test, transglycosylation activity of GS3-3 was obtained at 16.61 U/mL. The mycelia of GS3-3 were reused ten times to produce IMO syrup from liquefied cassava starch containing about 280 g/L total sugar within 4 days. The conversion of liquefied cassava starch to IMO was at 71.3-72.1 %, which was higher than the best conversion (68 %) ever reported. GS3-3 shows a great potential for industrial IMO production.
异麦芽低聚糖（IMO）是一种用作食品添加剂的葡萄糖苷，由糖化淀粉经具有转糖苷活性的酶或微生物细胞制成。本研究旨在通过基因重排技术产生具有增强转糖苷活性的黑曲霉突变体，用于工业 IMO 生产。起始突变体群体由（60）Co-γ射线产生；选择具有更高转糖苷活性的突变体，并进行递归原生质体融合。所得融合子通过一种基于检测非发酵还原糖的新型高通量筛选方法进行筛选。经过三轮基因组重排，获得了性能最佳的菌株 GS3-3，其转糖苷活性（14.91 U/mL）比原始菌株 C-6181 提高了 194.1%。在发酵罐试验中，GS3-3 的转糖苷活性达到 16.61 U/mL。GS3-3 的菌丝体在 4 天内重复使用十次，从含有约 280 g/L 总糖的液化木薯淀粉中生产 IMO 糖浆。液化木薯淀粉转化为 IMO 的转化率为 71.3-72.1%，高于以往报道的最佳转化率（68%）。GS3-3 具有很大的工业 IMO 生产潜力。
