Full Length Research Paper

Thermoactive cellulase-free xylanase production from alkaliphilic Bacillus strains using various agro-residues and their potential in biobleaching of kraft pulp

Cem Azeri, Abdurrahman U. Tamer and Mustafa Oskay*

Biology Department, Faculty of Sciences and Arts, Celal Bayar University, Manisa, Turkey.

*Corresponding author. E-mail: mustafa.oskay@bayar.edu.tr.

Accepted 5 November, 2009

   Abstract

The four bacterial strains were isolated on media containing xylan and screened for xylanase activity. The bacterial strains (Ag12, Ag13, Ag20 and Ag32) were characterized based on morphological, biochemical and physiological characters and identified as belonging to the genus Bacillus. The effects of different factors such as pH (7.0 – 10.0), temperature (25.0 – 50.0°C) and inexpensive agro-residues (wheat straw, wheat bran and corncob) on xylanase production of strains were studied under shake flask conditions. Maximal enzyme activities were obtained by cultivation in birch-wood xylan, but high enzyme production was also obtained on wheat straw and corncob when cultivated at pH 8.5. Under optimized fermentation conditions, no cellulolytic activity were detected on the crude extracts. The effects of temperature (40.0 – 80.0°C), pH (6.0 – 10.0) and salt concentration (1.0, 5.0 and 10.0%) on the xylanases activity were determined. The maximum activity was obtained temperature 60.0°C and pH at 9.0. The enzyme was stable at 60.0°C for more than 60 min, suggesting that the xylanases of Bacillus strains are thermoactive and being of interests for biobleaching processes. The effectiveness of crude xylanases from the strains Ag12, Ag20 and Ag32 on kraft pulp were carried out at pH 9.0 at 60.0°C. Biobleaching studies of kraft pulp with xylanases and its subsequent treatment with 1.0% EDTA (30 min at 50.0°C) and peroxide (80 min at 70.0°C), showed that the enzymes reduced the kappa number by 27.4, 61.7 and 75.3% and enhanced the brightness by 1.0, 1.5 and 3.0% from xylanases produced by strains Ag12, Ag20 and Ag32, respectively. These results suggest that the application of this xylanases to the paper and pulp industry may be very promising.

Key words: Alkaliphilic Bacillus, biobleaching, brightness, cellulase-free xylanase, chromophore release, kappa number, kraft pulp, pretreatment, xylanase applications.