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Abstract:
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Xylanases with hydrolytic activity on xylan, one of the hemicellulosic
materials present in plant cell walls, have been identified long back and the
applicability of this enzyme is constantly growing. All these applications
especially the pulp and paper industries require novel enzymes. There has
been lot of documentation on microbial xylanases, however, none meeting all
the required characteristics. The characters being sought are: higher
production, higher pH and temperature optima, good stabilities under these
conditions and finally the low associated cellulase and protease production.
The present study analyses various facets of xylanase biotechnology giving
emphasis on bacterial xylanases. Fungal xylanases are having problems like
low pH values for both enzyme activity and growth. Moreover, the associated
production of cellulases at significant levels make fungal xylanases less
suitable for application in paper and pulp industries.Bacillus SSP-34 selected from 200 isolates was clearly having xylan
catabolizing nature distinct from earlier reports. The stabilities at higher
temperatures and pH values along with the optimum conditions for pH and
temperature is rendering Bacillus SSP-34 xylanase more suitable than many of
the previous reports for application in pulp and paper industries.Bacillus SSP-34 is an alkalophilic thertmotolerant bacteria which
under optimal cultural conditions as mentioned earlier, can produce 2.5 times
more xylanase than the basal medium.The 0.5% xylan concentration in the medium was found to the best
carbon source resulting in 366 IU/ml of xylanase activity. This induction was
subjected to catabolite repression by glucose. Xylose was a good inducer for
xylanase production. The combination of yeast extract and peptone selected
from several nitrogen sources resulted in the highest enzyme production
(379+-0.2 IU/ml) at the optimum final concentration of 0.5%. All the cultural
and nutritional parameters were compiled and comparative study showed that the modified medium resulted in xylanase activity of 506 IU/ml, 5 folds higher than the basal medium.The novel combination of purification techniques like ultrafiltraton,
ammonium sulphate fractionation, DEAE Sepharose anion exchange
chromatography, CM Sephadex cation exchange chromatography and Gel
permeation chromatography resulted in the purified xylanase having a specific
activity of 1723 U/mg protein with 33.3% yield. The enzyme was having a
molecular weight of 20-22 kDa. The Km of the purified xylanase was 6.5 mg
of oat spelts xylan per ml and Vmax 1233 µ mol/min/mg protein.Bacillus SSP-34 xylanase resulted in the ISO brightness increase from
41.1% to 48.5%. The hydrolytic nature of the xylanase was in the endo-form.Thus the organism Bacillus SSP-34 was having interesting
biotechnological and physiological aspects. The SSP-34 xylanase having
desired characters seems to be suited for application in paper and pulp
industries. |