PRODUCTION AND CHARACTERIZATION OF AN Aspergillus niger GS1S6 PHYTASE CULTIVATED IN PHYTIC ACID-RICH AGRICULTURAL SUBSTRATES

PRODUCTION AND CHARACTERIZATION OF A FUNGAL PHYTASE

Abstract

In animal farming, improvement of growth performance through successful nutrient uptake and digestibility is critical. Phytases hydrolyze the anti-nutritive phytic acid present in grains to lesser derivatives and release the phosphorus trapped therein. Twenty-eight fungi obtained from poultry droppings, cereal-rich soils and garden soils were screened for phosphate solubilization and phytase production using Pikovskaya agar and phytase screening medium. Out of the fungi, 61% were positive for phytase producing abilities and the most proficient, isolate GS₁S₆ with a solubilization index of 121%, was identified as Aspergillus niger GS₁S₆. Optimum phytase production was achieved at a fermentation period of 120 h, pH 5.5, glucose, (NH₄)₂SO₄ using 72 hour old fungal inoculum. Mineral supplementation of natural agricultural substrates enhanced phytase production (1000U/L) the most in milled sesame seed medium. The ~31-38 KDa partially purified and characterized enzyme demonstrated optimum activities at 55^oC and pH 6.0, while cationic inclusions reduced phytase activities. The K_m and V_max were low (1.308 mM and 0.077 mM/mL/min) from Linear-weaver plot with increasing substrate concentration implying that A. niger GS₁S₆ phytase may efficiently mineralize phytic acid and therefore hold great prospect for its commercialization.