Abstract

The production, purification, and characterization of thermostable-alkaline keratinase from Bacillus halodurans SW-X (keratinase_SW-X), and its applicability towards the production of white chicken feather hydrolysate and bioplastic starch/keratin production were investigated. A maximal keratinase activity of 16.05 ± 0.25 U/mL was achieved by cultivation of B. halodurans SW-X in 5 L stirred tank bioreactor at 47 °C, 200 rpm, and 2 vvm for 48 h. Keratinase_SW-X was purified as a monomeric protein with the estimated MW of 25 kDa, 14.4-fold, and 20% recovery yield. The protein was classified as thermostable-alkaline keratinase due to its optimal pH (pH 10) and temperature (70 °C), pH stability (pH 9.0–11), thermostability (> 3 h at 50–60 °C), and it showed the highest specificity towards chicken feather keratin with K_m of 0.45 mg/mL, and V_max of 3.51 μmol/min/mg. Crude keratinase_SW-X biodegraded white chicken feathers into two types of low (10–20 kDa) and high (≥ 30 kDa) chicken feather (keratin) hydrolysates, with total recovery yields of 30%. The bioplastic starch/keratin was synthesized using cassava starch (70%, w/w), glycerol (30%, w/w), and keratin hydrolysate (0–0.30%, w/w). The optimal concentration of keratin hydrolysate was 0.10% (w/w), resulting in improved strength and elongation at break, with a good appearance of the bioplastic starch/keratin. Our study suggests that B. halodurans SW-X is a potential strain for thermostable-alkaline keratinase production. Moreover, from environmental perspectives, keratinases_SW-X is a promising candidate enzyme that valorizes low cost chicken feather waste to a high value added product, indicating a novel approach for feather waste treatment and utilization.

Graphic Abstract

中文翻译：

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嗜盐芽孢杆菌SW-X的热稳定碱性角蛋白酶的生化特性及其在鸡羽废物中的价值评估

摘要

研究了嗜盐芽孢杆菌SW-X（角蛋白酶_SW-X）的热稳定碱性角蛋白酶的制备，纯化和表征，及其在白羽鸡羽毛水解产物生产和生物塑料淀粉/角蛋白生产中的适用性。通过培养嗜盐芽孢杆菌可达到最大的角蛋白酶活性16.05±0.25 U / mL在47°C，200 rpm和2 vvm的5 L搅拌釜生物反应器中进行SW-X 48小时。纯化的角蛋白酶_SW-X为单体蛋白，估计分子量为25 kDa，14.4倍和20％的回收率。由于该蛋白的最佳pH（pH 10）和温度（70°C），pH稳定性（pH 9.0-11），热稳定性（在50-60°C，> 3 h），因此被归类为热稳定碱性角蛋白酶。对鸡羽毛角蛋白具有最高的特异性，K _m为0.45 mg / mL，V _max为3.51μmol/ min / mg。粗角蛋白酶_SW-X将白色鸡羽毛生物降解为低（10–20 kDa）和高（≥30 kDa）高（≥30 kDa）鸡羽毛（角蛋白）水解产物，总回收率为30％。使用木薯淀粉（70％，w / w），甘油（30％，w​​ / w）和角蛋白水解产物（0-0.30％，w​​ / w）合成生物塑料淀粉/角蛋白。角蛋白水解物的最佳浓度为0.10％（w / w），从而提高了强度和断裂伸长率，并具有良好的生物塑料淀粉/角蛋白外观。我们的研究表明，嗜盐芽孢杆菌SW-X是生产热稳定碱性角蛋白酶的潜在菌株。而且，从环境角度来看，角蛋白酶_SW-X是一种有前途的候选酶，它可以将低成本的鸡羽毛废料增值为高附加值产品，这表明了一种处理和利用羽毛废料的新方法。

图形摘要