Abstract:
Phytic acid is the major storage form of phosphorous in plants, legumes and oil plant seeds. Phytate-degrading enzymes have been detected in various microorganisms. This project was targeted at isolating microorganisms from degrading leaf litters (Tectona grandis) in soil environment and snail (Archachatina marginata) as well to screen the isolates for the production of phytase. Effect of physical parameters such as substrate concentration, temperature, pH and stability were considered in the production of phytase. Thermostability of the enzymes phytase was assessed after exposure to high temperature. Measurement of residual activity after heat exposure was made under different conditions (buffer, time, temperature). Eight fungi; Articulospora inflata, Fusarium culmorum, Aspergilus niger, A. fumigatus, A. flavus, Penicillium chrysogenum, Rhizopus stolonifer, Penicillium italicum were isolated from soil samples while five fungi Cladosporium sphaeropermum, Varicosporum eloedea, Plerothecium recurvatum, Trichoderma viridae and Saccharomyces cerevisiae were isolated from snail (Archachatina marginata) samples. In all, ten bacteria were obtained from soil samples containing degraded leaf litters of Tectona grandis. Most of these isolates were Gram positive. These were Micrococcus lutens, Bacillus licheniformis, B. pumilus, B. sphaericus, B. sterothermophilus, B. coagulans, B. cereus, Staphylococcus aureus, Pseudomonas aeruginosa and Proteus vulgais. Aspergillus fumigatus and A.niger were selected for phytase production based on their growth profile. There was a progressive increase in phytase production up to the third day of incubation with an activity of 0.081U/ml for A. fumigatus and 0.0178U/ml for A. niger. The protein content of A. fumigatus was maximum at day 3 while for A. niger, protein content was maximum at day 5. There was also decrease in phytase activity with increase in substrate concentration for both A. fumigatus and A. niger. The optimum pH for phytase production was 4.5. There was decrease in stability of phytase with increase in time. The relative high thermostability of this enzyme was confirmed. It was also shown that these measurements were very sensitive to the selected buffer system. The high stability of the A. fumigatus and A. niger phytase may be based on the ability jof the enzyme to refold to native like fully active conformation after heat denaturation.
