Asian Journal of Biotechnology and Genetic Engineering

Samples for isolation were taken from natural spoiled salted foods. All acidophilic isolates were subjected under comparison for finding the most potent glutaminase producing one. Optimization of the produced enzyme was done in the light of seven environmental and five nutritional factors including incubation time, temperature, pH, buffer system, static and different shaking speeds conditions, dark and light conditions, different inoculum size, additional carbon sources, additional nitrogen sources, heavy metals, vitamins, amino acids. Five fungal isolates have been selected and were tested for their ability to grow on L- glutamine containing medium at pH 3 and 2. Only 5 fungal isolates (F1.a, F2.a, F3.a, F4.a and F5.a) were able to grow efficiently on pH3, two of them were able to grow also on pH2. The activity of enzyme was measured extracellularly and intracellularly for each isolate and were 20.34, (2.68), 17.8, (0.423), 5.77, (5.77), 10.27, (1.39), 2.28 and (0.071) U/mL respectively. The highest enzyme activity producing isolate (F1.a) was selected and identified genetically. It was found to be closely related to Aspergillus niger strain CPGM 1439 with 93% homology and accession number DQ196192.1. The yield was quiet high after optimization reached 49.59 U/mL extracellularly which is essential advantage for such production method. The maximum yield was obtained at 35°C, pH1.8, 100 ppm Mn⁺², addition of iso- leucine 3.59% for 7 days incubation in dark condition and shaking speed 100 rpm. Glutaminase enzyme was produced efficiently by the finally selected acidophilic Aspergillus niger isolate and optimization lead to higher enzyme activity which was measured by U/mL in each step.