Keratinases are promising alternatives over ordinary proteases in several industrial applications due to their unique properties compared with their counterparts in the protease categories. However, their large-scale industrial application is limited by the low expression and poor fermentation efficiency of keratinase. Here, we demonstrate that the expression level of keratinase can be improved by constructing a more efficient enzyme expression system hereby enables the highest production titer as regarding recombinant keratinase production to date. Specially, ten promoters were evaluated and the aprE promoter exhibits a significant promotion of keratinase (kerBv) titer from 165 U/mL to 2605 U/mL in Bacillus subtilis. The batch fermentation mode resulted in a maximum keratinase activity of 7176 U/mL at 36 h in a 5-L fermenter. Furthermore, the extracellular keratinase activity attained up to 16,860 U/mL via fed-batch fermentation within 30 h. The combination of keratinase with l-cysteine brings about 66.4 % degree of degradation of feather. Our work provides a new insight into the development of efficient keratinase fermentation processes with B. subtilis cell factory.

中文翻译：

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通过启动子工程策略有效表达角蛋白酶以降解羽毛废物

由于与蛋白酶类别中的对应物相比，角蛋白酶具有独特的性质，因此在几种工业应用中是普通蛋白酶的有前途的替代品。然而，它们的大规模工业应用受到角蛋白酶的低表达和低发酵效率的限制。在这里，我们证明可以通过构建更有效的酶表达系统来提高角蛋白酶的表达水平，从而实现迄今为止重组角蛋白酶生产的最高生产滴度。特别地，评估了 10 个启动子，aprE 启动子在枯草芽孢杆菌中表现出显着促进角蛋白酶 (kerBv) 滴度从 165 U/mL 到 2605 U/mL。在 5 L 发酵罐中，分批发酵模式在 36 小时时产生的最大角蛋白酶活性为 7176 U/mL。此外，通过补料分批发酵，细胞外角蛋白酶活性在 30 小时内达到了 16,860 U/mL。角蛋白酶与 l-半胱氨酸的结合带来了大约 66.4% 的羽毛降解程度。我们的工作为开发枯草芽孢杆菌细胞工厂的高效角蛋白酶发酵工艺提供了新的见解。