Laba Wojciech, Rodziewicz Anna
Department of Biotechnology and Food Microbiology, Wroclaw University of Environmental and Life Sciences, Wroclaw, Poland.
Jundishapur J Microbiol. 2014 Feb;7(2):e8896. doi: 10.5812/jjm.8896. Epub 2014 Feb 1.
Extensive quantities of keratinic by-products are disposed annually by animal-processing industry, causing a mounting ecological problem due to extreme resilience of these materials to enzymatic breakdown. There is a growing trend to apply cheap and environment-friendly methods to recycle keratinic wastes. Soil bacteria of profound keratinolytic potential, especially spore-forming rods from the genus Bacillus, play a significant role in keratinase-mediated biodegradation of keratins, therefore could be effective in hastening their biodegradation. Keratin hydrolysis in microbial cultures is one of the most promising techniques not only to utilize this protein but also to obtain valuable by products.
The study was undertaken to investigate the biodegradation process of various keratinic materials by two Bacillus strains.
Two keratinolytic strains, Bacillus cereus and B. polymyxa, were subject to cultures in the presence of several keratinic appendages, like chicken feathers, barbs and rachea of ostrich feathers, pig bristle, lamb wool, human hair and stratum corneum of epidermis, as main nutrient sources. Bacterial ability to decompose these waste materials was evaluated, at the background of keratinase and protease biosynthesis, in brief four-day cultures. Keratinolytic activity was measured on soluble keratin preparation and proteases were assayed on casein. Additionally, amounts of liberated proteins, amino acids and thiols were evaluated. Residual keratin weight was tested afterwards.
Both tested strains proved to be more adapted for fast biodegradation of feather β-keratins than hair-type α-keratins. B. cereus revealed its significant proteolytic potential, especially on whole chicken feathers (230 PU) and stratum corneum (180 PU), but also on separated barbs and rachea, which appeared to be moderate protease inducers. Keratinolytic activity of B. cereus was comparable on most substrates and maximum level obtained was 11 KU. B. polymyxa was found to be a better producer of keratinases, up to 32 KU on chicken feathers and 14 KU on both fractions of ostrich feathers. Its proteolytic activity was mostly revealed on stratum corneum and human hair. Stratum corneum was extensively degraded by both bacterial strains up to 99% - 87%, chicken feathers 47-56%, ostrich barbs and rachea, 28% and 35% at maximum, respectively. Keratin fibres of structures like human hair, lamb wool and pig bristle remained highly resilient to this short microbiological treatment, however certain extent of keratinase induction was also observed.
The obtained results prove that keratinolytic potential of both tested bacterial strains could be applied mainly in biodegradation of feathers, however, B. cereus and B. polymyxa differed in terms of keratinase and protease production on each of the substrates. Biodegradation of highly resilient structures like hair or pig bristle requires further analysis of process conditions.
动物加工业每年都会产生大量角蛋白副产物，由于这些材料对酶解具有极强的抵抗力，导致生态问题日益严重。采用廉价且环保的方法回收角蛋白废料的趋势正在不断增长。具有强大角蛋白分解潜力的土壤细菌，尤其是芽孢杆菌属的芽孢形成杆菌，在角蛋白酶介导的角蛋白生物降解中发挥着重要作用，因此可能有效地加速其生物降解。微生物培养中的角蛋白水解是最具前景的技术之一，不仅可以利用这种蛋白质，还能获得有价值的副产品。
本研究旨在调查两种芽孢杆菌菌株对各种角蛋白材料的生物降解过程。
将两种角蛋白分解菌株，蜡样芽孢杆菌和多粘芽孢杆菌置于含有几种角蛋白附属物的培养基中培养，这些角蛋白附属物包括鸡毛、鸵鸟毛的羽支和羽轴、猪鬃、羊毛、人发以及表皮角质层，作为主要营养源。在以角蛋白酶和蛋白酶生物合成作为背景的情况下，通过为期四天的培养来评估细菌分解这些废料的能力。在可溶性角蛋白制剂上测量角蛋白分解活性，在酪蛋白上测定蛋白酶活性。此外，还评估了释放的蛋白质、氨基酸和硫醇的量。之后测试剩余角蛋白的重量。
两种受试菌株均被证明比毛发型α - 角蛋白更适合快速生物降解羽毛β - 角蛋白。蜡样芽孢杆菌显示出显著的蛋白水解潜力，特别是对整根鸡毛（230 PU）和角质层（180 PU），但对分离的羽支和羽轴也有作用，它们似乎是中度蛋白酶诱导剂。蜡样芽孢杆菌在大多数底物上的角蛋白分解活性相当，最高水平为11 KU。多粘芽孢杆菌被发现是更好的角蛋白酶生产者，在鸡毛上可达32 KU，在鸵鸟毛的两个部分上均为14 KU。其蛋白水解活性主要在角质层和人发上表现出来。两种细菌菌株对角质层的降解程度高达99% - 87%，对鸡毛的降解率最高分别为47 - 56%，对鸵鸟毛羽支和羽轴的降解率分别最高为28%和35%。人发、羊毛和猪鬃等结构的角蛋白纤维对这种短期微生物处理仍具有高度抗性，不过也观察到了一定程度的角蛋白酶诱导。
所得结果证明，两种受试细菌菌株的角蛋白分解潜力主要可应用于羽毛的生物降解，然而，蜡样芽孢杆菌和多粘芽孢杆菌在每种底物上的角蛋白酶和蛋白酶产生方面存在差异。对头发或猪鬃等高抗性结构的生物降解需要进一步分析工艺条件。
