Relatedness of Thermomyces lanuginosus strains producing a thermostable xylanase

Abstract

Properties of an endo-β-xylanase produced by a locally isolated Thermomyces lanuginosus strain SSBP was compared to seven other T. lanuginosus strains isolated from different geographical regions. Strain SSBP produced the highest xylanase activity of 59 600 nkat ml−1 when cultivated on corn cobs (maize) medium, whereas the seven other strains produced xylanase activities ranging from 6000 to 32 000 nkat ml−1. No cellulase activity was produced by the strains. Despite the variability in the production of xylanase, little difference in the other characteristics of the strains could be found. The optimal temperature and pH for xylanase production by the strains was either 40 or 50°C and between pH 6 and 7, respectively. Optimal xylanase activity of the strains was observed at 70°C and at pH 6 or 6.5. Culture supernatant analysis by SDS-PAGE and isoelectric focusing PAGE of all strains revealed the presence of a single 24.7 kDa and pI 3.9 xylanase. Phylogenetic analysis by PCR amplification and sequencing of the internal transcribed spacer of nuclear rRNA repeat units and 5.8S rDNA revealed no strain diversity. However, random amplified polymorphic DNA analysis pointed to greater diversity and with one primer (5′-GCCCGACGCG-3′), a relationship was established between xylanase levels and the RAPD pattern.