Production, optimisation and characterisation of L-asparaginase from Bacillus subtilis SSB55 and Aspergillus flavus SSF23

L-asparaginase is extensively used in medicine for treating leukaemia and preventing acrylamide formation in the food industry. L-asparagine is hydrolysed to ammonia and L-aspartic acid by L-asparaginase, leading to depletion of circulating L-asparagine required for the survival of certain tumour cells. This work investigated the production, optimisation, and characterisation of L-asparaginase from microbes isolated from soil samples. Bacteria and fungi were isolated from different soil samples collected from Ajayi Crowther University, Oyo, Nigeria, using the pour plate method. The isolated microbes were initially screened for L-asparaginase production on agar plates. The selected L-asparaginase producers were assayed for enzyme activity using the Nesslerisation method. The most promising producers were molecularly identified. L-asparaginase production was optimised using different parameters, and the enzyme activities were characterised. Out of 65 bacterial isolates, 25 produced L-asparaginase, while 18 out of 73 fungal isolates did the same on plates. The top bacterial and fungal producers were identified as Bacillus subtilis SSB55 and Aspergillus flavus SSF23, respectively. Optimal production of L-asparaginase (16553 U/mL) by Bacillus subtilis SSB55 was achieved using lactose as the carbon source and ammonium nitrate as the nitrogen source at pH 7.0, with a 5% (v/v) inoculum of 1.5 × 10 8 CFU/mL in the fermentation medium over 48 h. Aspergillus flavus SSF23 reached maximum L-asparaginase production (19047 U/mL) using a medium containing fructose as the carbon source and ammonium nitrate as the nitrogen source at pH 7.0, with three circular plugs (7 mm diameter) of inoculum over 96 h. The highest enzyme activities at different incubation temperatures were observed at 60 °C for Bacillus subtilis SSB55 (24513 U/mL) and at 25 °C for Aspergillus flavus SSF23 (20327 U/mL). L-asparaginase activities were significantly affected by pH, metal ions, and their concentrations (ρ ≤ 0.05). L-asparaginase yields of Bacillus subtilis SSB55 and Aspergillus flavus SSF23 were optimised, and different environmental conditions, metal ions and their concentrations significantly influenced their activities. Clinical Trial Number: Not applicable