Diversification of nitrogen sources as a tool to improve endo-xylanase enzyme activity produced by Cryptococcus laurentii

Cryptococcus laurentii: a wild yeast for xylanase production from agricultural by-products

The development of technologies that allow the production of enzymes at a competitive cost is of great importance for several biotechnological applications, and the use of agro-industrial by-products is an excellent alternative to minimize costs and reduce environmental impacts. This study aimed to produce endo-xylanases using agro-industrial substrates rich in hemicellulose as sources of xylan in culture media. For this purpose, the yeast Cryptococcus laurentti and five lignocellulosic materials (defatted rice bran, rice husk, corn cob, oat husks, and soybean tegument), with and without pretreatment, were used as a source of xylan for enzyme production. To insert the by-products in the culture medium, they were dried and treated (if applicable) with 4% (w.v-1) NaOH and then added in a concentration of 2% (w.v-1). The cultures were agitated for 96 h, and the aliquots were removed to determine the enzymatic activities. Among the by-products studied, the maximum activity (8.7 U. mL-1 at pH 7.3) was obtained where rice bran was used. In contrast, corn cob was the by-product that resulted in lower enzyme production (1.6 U.mL-1). Thus, the defatted rice bran deserves special attention in front of the other by-products used since it provides the necessary substrate for producing endo-xylanases by yeast.

Valorization of lignocellulosic wastes for sustainable xylanase production from locally isolated Bacillus subtilis exploited for xylooligosaccharides' production with potential antimicrobial activity

The worldwide availability of lignocellulosic wastes represents a serious environmental challenge with potential opportunities. Xylanases are crucial in lignocellulosic bio-hydrolysis, but the low enzyme productivity and stability are still challenges. In the current study, Bacillus subtilis (coded ARSE2) revealed potent xylanase activity among other local isolates. The enzyme production optimization revealed that maximum enzyme production (490.58 U/mL) was achieved with 1% xylan, 1.4% peptone, and 5% NaCl at 30 °C and pH 9. Furthermore, several lignocellulosic wastes were exploited for sustainable xylanase production, where sugarcane bagasse (16%) under solid-state fermentation and woody sawdust (2%) under submerged fermentation supported the maximum enzyme titer of about 472.03 and 485.7 U/mL, respectively. The partially purified enzyme revealed two protein bands at 42 and 30 kDa. The partially purified enzyme revealed remarkable enzyme activity and stability at 50-60 °C and pH 8-9. The enzyme also revealed significant stability toward tween-80, urea, DTT, and EDTA with Vmax and Km values of 1481.5 U/mL and 0.187 mM, respectively. Additionally, the purified xylanase was applied for xylooligosaccharides production, which revealed significant antimicrobial activity toward Staphylococcus aureus with lower activity against Escherichia coli. Hence, the locally isolated Bacillus subtilis ARSE2 could fulfill the xylanase production requirements in terms of economic production at a high titer with promising enzyme characteristics. Additionally, the resultant xylooligosaccharides revealed a promising antimicrobial potential, which paves the way for other medical applications.

Cellulolytic and Xylanolytic Enzymes from Yeasts: Properties and Industrial Applications

Lignocellulose, the main component of plant cell walls, comprises polyaromatic lignin and fermentable materials, cellulose and hemicellulose. It is a plentiful and renewable feedstock for chemicals and energy. It can serve as a raw material for the production of various value-added products, including cellulase and xylanase. Cellulase is essentially required in lignocellulose-based biorefineries and is applied in many commercial processes. Likewise, xylanases are industrially important enzymes applied in papermaking and in the manufacture of prebiotics and pharmaceuticals. Owing to the widespread application of these enzymes, many prokaryotes and eukaryotes have been exploited to produce cellulase and xylanases in good yields, yet yeasts have rarely been explored for their plant-cell-wall-degrading activities. This review is focused on summarizing reports about cellulolytic and xylanolytic yeasts, their properties, and their biotechnological applications.