THERMOPHILIC AND ALKALOPHILIC XYLANASES FROM SEVERAL DICTYOGLOMUS-ISOLATES

Supernatant xylanases from three thermophilic and strictly anaerobic Dictyoglomus strains isolated from very different environments were examined: the type species, D. thermophilum(T), 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 x 10(-6) kat l-1. The K(m) 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-degrees-C, maximum temperature for extended activity between 80 and 90-degrees-C, and a thermal half-life of over 1 h at 90-degrees-C for strain B1. The application of thermophilic alkalophilic xylanases to paper pulping was discussed.