L-methioninase production by filamentous fungi: I-screening and optimization under submerged conditions.

Findings show 21 fungal isolates belonging to eight genera recovered from Egyptian soils that have the potential to attack L-methionine under submerged conditions. Aspergillus flavipes had the most methioninolytic activity, giving the highest yield of L-methioninase (10.78 U/mg protein), rate of methionine uptake (93.0%), and growth rate (5.0 g/l), followed by Scopulariopsis brevicaulis and A. carneus. The maximum L-methioninase productivity (11.60 U/mg protein) by A. flavipes was observed using L-methionine (0.8%) as an enzyme-inductive agent and glucose (1%) as a co-dissimilated carbon source. A significant reduction in L-methioninase biosynthesis by A. flavipes was detected using carbon-free medium, suggesting the lack of ability to use L-methionine as a carbon and nitrogen source. Potassium dihydrogen phosphate (0.25%), the best source of phosphorus, favors enzyme biosynthesis and enhances the level of methionine uptake by A. flavipes. The maximum L-methioninase productivity (12.58 U/mg protein) and substrate uptake (95.6%) were measured at an initial pH of 7.0.