Abstract
Supernatant xylanases from three thermophilic and strictly anaerobic Dictyoglomus strains isolated from very different environments were examined: the type species, D. thermophilumT, from a hot-spring in Japan; strain B1, a recently described strictly xylan-utilizing Dictyoglomus from a paper-pulp factory in Finland; and strain B4a, isolated from a thermal pool on Iceland. The highest enzymatic activity observed from batch-culture supernatant with 4 g l−1 of beech xylan as growth substrate was 3.8 × 10−6 kat l−1. The Km for the xylanases of strain B1 was 4.7 g beech xylan l−1. The xylanases of all the isolates had a broad range of activity with respect to pH, showing good activity from pH 5.5 to near 9.0. The xylanases from the three isolates had a very high temperature optimum of 80°C, maximum temperature for extended activity between 80 and 90°C, and a thermal half-life of over 1 h at 90°C for strain B1. The application of thermophilic alkalophilic xylanases to paper pulping was discussed.
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