132 microorganisms, isolates from soil and decayed fruits, were tested for phytase production. All isolates intensively producing active extracellular phytase were of fungal origin. The most active fungal isolates with phytase activity were identified as Aspergillus niger. At the end of the growth phase, the extracellular phytase activity produced by A. niger strain 92 was 132 nkat/mL, with strain 89 it was 53 nkat/mL. In both strains the extracellular enzyme activity exhibited two marked activity optima at pH 1.8 and 5.0 and a temperature optimum at 55 degrees C.

The extracellular activity of Aspergillus niger phytase at the end of the growth phase was 132 nkat/mL in a laboratory bioreactor. The purified enzyme has molar mass approximately 100 kDa, pH optimum at 5.0, temperature optimum at 55 degrees C and high pH and temperature stability. The Km for dodecasodium phytate, calcium phytate and 4-nitrophenyl phosphate are 0.44, 0.45 and 1.38 mmol/L, respectively. The enzyme is noncompetively inhibited by inorganic monophosphate (Ki = 2.85 mmol/L) and by Cu2+, Zn2+, Hg2+, Sn2+, Cd2+ ions and strongly by F- ones; it is activated by Ca2+, Mg2+ and Mn2+ ions. The substrate specificity of phytase is broad with the highest affinity to calcium phytate.

Xylanase activity was found both free and bound to the cells and (or) the substrate during the first growth phase of Cellulomonas on bagasse pith. At the same time, rapid degradation of the bagasse hemicellulose was observed. The enzymes became bound mainly during the second growth phase, during which hemicellulose degradation was still detected, although at a lower rate. Intracellular xylanase activity was about one-tenth of the activity detected outside the cell during this phase. At the end of growth, 89% of the bagasse hemicellulose had been consumed.

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