“Studies on the production of microbial L-asparaginase”

Abstract

Two hundred soil samples collected from different Egyptian governorates were used for recovery of seven hundred and twenty two isolates. The recovered isolates were screened for L-asparaginase production on modified M9 medium supplemented with phenol red as an indicator and 1% w/v asparagine. A total of 81 isolates were proved to be L-asparaginase producers and they were categorized into Gram positive (70 isolates) and Gram negative (11 isolates) according to their Gram reaction. Then, the eighty one producing isolates were subsequently quantified for their L-asparaginase productivity using Nesslerization reaction. The L-asparaginase producing isolates were further categorized into high producers (isolates productivity ≥ 3 IU/ml/h), intermediate producers (isolates productivity ≥ 1 < 3 IU/ml/h) and low producers (isolates productivity < 1 IU/ml/h). The highest Gram positive and Gram negative producing isolates were identified using Biolog® and Vitek® system, respectively then their identification were confirmed by 16S rRNA gene sequencing to be Bacillus licheniformis and Stenotrophomonas maltophilia. The assembled sequences of the two isolates were deposited in GenBank database with assigned accession codes of MG665995 for Bacillus licheniformis and MG665996 for Stenotrophomonas maltophilia. L-asparaginase produced from Bacillus licheniformis was relatively thermostable compared to that of Stenotrophomonas maltophilia where the activity of the former retained about 70% of its activity at 70°C/30 min while that of the later preparation retained only 55% of its activity. L- asparaginase activity was assessed at different temperatures where the two isolates showed optimum activities at 37-40°C. The catalytic activity of both enzyme preparations decreased at 45°C by 27.7% in case of Bacillus licheniformis and 21%