Biochemical and biological evaluation of L-glutaminase from Aspergillus tamarii AUMC 10198 via solid-state...

Fungal L-glutaminase has recently attracted growing interest due to its potential applications in medical therapy and biotechnology. This study aimed to develop a cost-effective bioprocess for L-glutaminase production using agricultural by-products under solid-state fermentation (SSF). Several fungal isolates were screened for extracellular L-glutaminase production, and the native isolated strain Aspergillus tamarii AUMC 10198 was identified as a potent high-yield producer. Process parameters influencing enzyme production were systematically optimized using a one-variable-at-a-time (OVAT) approach. The enzyme was subsequently purified through a three-step procedure and characterized for its biochemical properties. Notably, the purified L-glutaminase also exhibited antimicrobial activity, suggesting potential therapeutic applications.

The native fungus Aspergillus tamarii AUMC 10198, registered under GenBank accession number OQ976977, was identified as a potent producer of L-glutaminase under solid-state fermentation (SSF) using wheat bran as the solid substrate. The solid-state yield of L-glutaminase exhibited a 3.20-fold increase in comparison to the unoptimized state. L-glutaminase produced by Aspergillus tamarii AUMC 10198 was purified through three successive steps, leading to a 12.90-fold enhancement in enzyme activity. As a result of the purification process, the final enzyme recovery was 18.45%. The isolated L-glutaminase exhibited optimal activity at a pH of 8, a temperature of 45 °C, and partial stability up to 60 °C, as determined by characterization. The purified L-glutaminase exhibited a Vmax of 10.10 U/ml and a km of 0.28 mg/ml when glutamine was used as the substrate. The metal ions Fe²⁺, Ca²⁺, K⁺, Mg²⁺, and Na⁺ of 0.01 M concentration exhibited notable enzyme-activating effects, leading to an increase in L-glutaminase activity. The molecular mass was estimated to be approximately 62 kDa by SDS-PAGE. The produced enzyme showed notable antimicrobial activity, with the strongest effect against Staphylococcus aureus (36.80 ± 1.20 mm), followed by Bacillus subtilis (30.40 ± 0.60 mm), while the weakest inhibition was observed against Pseudomonas aeruginosa (12.80 ± 1.20 mm); moderate antifungal activity was also recorded highlighting its potential for broad therapeutic and pharmaceutical applications.

This study highlights the remarkable properties of L-glutaminase produced by the native potent fungal isolate Aspergillus tamarii AUMC 10198, underscoring its significant potential for industrial applications and pharmaceutical drug development.