Xylanases of marine fungi of potential use for biobleaching of paper pulp

Abstract

Microbial xylanases that are thermostable, active at alkaline pH and cellulasefree are generally preferred for biobleaching of paper pulp.. We screened obligate and facultative marine fungi for xylanase activity with these desirable traits.Several fungal isolates obtained from marine habitat showed alkaline xylanase activity. The crude enzyme from NIOCC isolate # 3 (Aspergillus niger) with high xylanase activity, cellulase-free and unique properties containing 580 U L -1 of xylanase, could bring about bleaching of sugarcane bagasse pulp by a 60 min treatment at 55 o C, resulting in a decrease of 10 kappa numbers and a 30% reduction in consumption of chlorine during bleaching process. The culture filtrate showed peaks of xylanase activity at acidic pH (3.5) and alkaline pH (8.5). When assayed at pH 3.5 optimum activity was detected at 50 o C with a second peak of activity at 90 o C. When assayed at pH 8.5 optimum activity was seen at 80 o C. The crude enzyme was thermostable at 55 o C for at least 4 h and retained about 60% of the activity. Gel filtration of the 50-80% ammonium sulfate precipitatedfraction of the crude culture filtrate separated into two peaks of xylanase having specific activities of 393 and 2457 U mg -1 protein. The two peaks showing xylanase activities had molecular masses of 13 and 18 kDa. Zymogram analysis of xylanase of crude culture filtrate as well as the 50-80% ammonium sulphateprecipitated fraction showed two distinct xylanase activity bands on native PAGE The crude culture filtrate also showed moderate activities of -xylosidase and -L-arabinofuranosidase which could act synergistically with xylanase in attacking xylan. This is the first report showing potential application of crude culture filtrate of a marine fungal isolate possessing thermostable, cellulase-free alkaline xylanase activity in biobleaching of paper pulp.

Xylanase and β-Xylosidase from Penicillium janczewskii: Production, Physico-chemical Properties, and Application of the Crude Extract to Pulp Biobleaching

“…The reduction obtained in the treatments with P. janczewskii xylanases was higher than to those obtained with some other fungal xylanases, which normally present reductions between 0.9 and 4.6 units in kappa number Madlala et al 2001;Maximo et al 1998;Medeiros et al 2007;Michelin et al 2010;Nair et al 2010;Peixoto-Nogueira et al 2009;Taneja et al 2002). Only one study reported greater reduction, i.e., 10.0, treating a cellulose pulp with A. niger xylanases (Raghukumar et al 2004).…”

Xylitol production byCyberlindnera(Williopsis) saturnus, a tropical mangrove yeast from xylose and corn cob hydrolysate

“…These fungi possess enzymes that display unique characteristics with respect to temperature, pH and salinity of the medium (Raghukumar 2008). Aspergillus (Raghukumar et al 2004) and Flavodon (D' Souza et al 2006) genera from mangroves have been known to produce cellulase, xylanase and lignin degrading enzymes having high titres and specific activities. The high salt concentration and low water potential of the mangrove ecosystem favour the growth of microbes that can maintain a lower water potential than the surrounding saline waters.…”

The fungal ability for biobleaching/biopulping/bioremediation of lignin-like compounds of agro-industrial raw material

“…The crude culture filtrate containing 580 U L -1 of xylanase could bring about bleaching of sugarcane bagasse pulp by a 60 min treatment at 55 °C, resulting in a decrease of ten units in the Kappa number (K nº) and 30% reduction in chlorine consumption during bleaching. 39 The K nº index is considered a measure of lignin content in wood.…”