The present invention relates to novel xylanases purified from the microorganism, Microtetraspora flexuosa. Each biochemically unique xylanase is thermostable and has optimal activity in alkaline conditions. The present invention is also directed to methods that utilize either the whole enzyme system or one or more of the above purified thermostable xylanases obtained from Microtetraspora flexuosa. These enzymes are excellent candidates for enhancing the delignification and bleaching of pulp. Furthermore, treating the pulp with the above enzymes prior to bleaching may reduce the amount of chlorine containing and/or peroxide chemicals required in the bleaching process.