Thermophilic Fungi

Thermophilic fungi are known to produce thermostable enzymes which have a number of applications, mainly in biotechnological processes. In this work, we report the characterization of a protease produced in state-solid (SSF) and submerged (SmF) fermentations by a newly isolated thermophilic fungus identified as a putative new species in the genus My-celiophthora. Enzyme-production rate was evaluated for both fermentation processes, and in SSF, using a media composed by a mixture of wheat bran and casein, the proteolytic output was 4.5-fold larger than that obtained in SmF. Additionally, the peak of proteolytic activity was obtained after 3 days for SSF whereas for SmF it was after 4 days. The crude enzyme obtained by both SSF and SmF displayed equivalent optimum temperature at 50ºC, however the optimum pH shifted from 7 (SmF) to 9 (SSF). The alkaline protease produced through solid-state fermentation (SSF), was immobilized on beads of calcium alginate, allowing to carry out comparative analyses of free and immobilized proteases. It was observed that both optimum temperature and thermal stability of the immobilized enzyme were higher then for the free enzyme. Moreover, the immobilized enzyme showed good stability for up to 7 reuses.

Keywords: alkaline protease, immobilized enzyme, Myceliophthora sp., solid state fermentation, thermophilic fungus.

Enzymes have a wide variety of biotechnological, biomedical, and pharmaceutical applications. Proteases constitute are the most important group of commercially available enzymes (Joo et al., 2002); they account for about 65% of the worldwide sale of industrial enzymes in the world market (Johnvesly and Naik, 2001). Microorganisms are an important source of proteases mainly due to t...

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...erature and pH on free and immobilized enzyme stability

The thermal stability was investigated by measuring the enzyme activity after keeping the enzyme solution for 1 h in the absence of substrate, at temperatures between 30 and 70°C in the absence of the substrate. The effect of pH on the stability was analyzed by incubating ali-quots of the enzyme at room temperature at pHs from 8 to 11 at 1, 3, 5 and 24 h. Remaining protease activity was determined at optimum pH and temperature.

Reusability of protease immobilized in the alginate beads

The initial activity of the immobilized enzyme was measured and the conjugate was then sub-jected to cycles of repeated use. The results of pH, temperature and reusability stability of free and immobilized protease are presented in a normalized form, with the highest value of each set being assigned the value of 100 % activity.