Gomes J, Gomes I, Steiner W
Institute of Biotechnology, Technical University Graz, Austria.
Extremophiles. 2000 Aug;4(4):227-35. doi: 10.1007/s007920070024.
Xylanase production by the Antarctic psychrophilic yeast Cryptococcus adeliae was increased 4.3 fold by optimizing the culture medium composition using statistical designs. The optimized medium containing 24.2 g l(-1) xylan and 10.2 g l(-1) yeast extract and having an initial pH of 7.5 yielded xylanase activity at 400 nkat (nanokatal) ml(-1) after 168-h shake culture at 4 degrees C. In addition, very little endoglucanase, beta-mannanase, beta-xylosidase, beta-glucosidase, alpha-L-arabinofuranosidase, and no filter paper cellulase activities were detected. Among 12 carbon sources tested, maximum xylanase activity was induced by xylan, followed by lignocelluloses such as steamed wheat straw and alkali-treated bagasse. The level of enzyme activity produced on other carbon sources appeared to be constitutive. Among the complex organic nitrogen sources tested, the xylanase activity was most enhanced by yeast extract, followed by soymeal, Pharmamedia (cotton seed protein), and Alburex (potato protein). A batch culture at 10 degrees C in a 5-1 fermenter (3.5-1 working volume) using the optimized medium gave 385 nkat at 111 h of cultivation. The crude xylanase showed optimal activity at pH 5.0-5.5 and good stability at pH 4-9 (21 h at 4 degrees C). Although the enzyme was maximally active at 45 degrees - 50 degrees C, it appeared very thermolabile, showing a half-life of 78 min at 35 degrees C. At 40 degrees - 50 degrees C, it lost 71%-95% activity within 5 min. This is the first report on the production as well as on the properties of thermolabile xylanase produced by an Antarctic yeast.
通过统计设计优化培养基成分，南极嗜冷酵母阿德利隐球酵母（Cryptococcus adeliae）产生木聚糖酶的能力提高了4.3倍。优化后的培养基含有24.2 g l⁻¹木聚糖和10.2 g l⁻¹酵母提取物，初始pH值为7.5，在4℃下振荡培养168小时后，木聚糖酶活性达到400 nkat（纳 Katal）ml⁻¹。此外，检测到的内切葡聚糖酶、β-甘露聚糖酶、β-木糖苷酶、β-葡萄糖苷酶、α-L-阿拉伯呋喃糖苷酶活性极低，且未检测到滤纸纤维素酶活性。在测试的12种碳源中，木聚糖诱导产生的木聚糖酶活性最高，其次是木质纤维素，如蒸麦秸和碱处理甘蔗渣。在其他碳源上产生的酶活性水平似乎是组成型的。在测试的复合有机氮源中，酵母提取物对木聚糖酶活性的增强作用最大，其次是豆粕、Pharmamedia（棉籽蛋白）和Alburex（马铃薯蛋白）。使用优化后的培养基在5升发酵罐（工作体积3.5升）中于10℃进行分批培养，培养111小时时木聚糖酶活性为385 nkat。粗木聚糖酶在pH 5.0 - 5.5时表现出最佳活性，在pH 4 - 9时具有良好的稳定性（4℃下21小时）。尽管该酶在45℃ - 50℃时活性最高，但它似乎非常不耐热，在35℃下的半衰期为78分钟。在40℃ - 50℃下，它在5分钟内失去71% -95%的活性。这是关于南极酵母产生的不耐热木聚糖酶的生产及其特性的首次报道。
