Isolation and Screening of L-asparaginase Producing Strains from Nature and its Optimization

L-asparaginase is an anti-neoplastic therapeutic agent used in the chemotherapy of lymphoblastic leukemia. Microorganisms are the best source for L-asparaginase production. The aim of this study was to isolate and identify l-asparaginase-producing bacteria from environmental samples. e. g. soil, water and different parts of plants.

The primary isolation was performed on nutrient agar (NA) and Luria Bertoni (LB) agar and then collected strains cultured on differential asparagine dextrose salts (ADS) agar medium. Asparaginase producing colonies were selected on the basis of formation of the pink color zone around the colonies. Colored colonies were selected for further enzyme activity studies using l-asparagine as a substrate. The amount of ammonia released was assayed by Nessler’s method and enzyme activity expressed as units per milligram of protein. The best strain was identified using morphological, biochemical and physiological characteristics and 16S rRNA sequence homology.

The results showed that among isolated strains, strain 105 exhibited high enzyme activity and was identified as Enterobacter sp. strain 105 that registered as accession number KX821734 in NCBI GenBank. The optimal enzyme-producing conditions were as follows: 1.5 % (w/v) starch as carbon source, 1.5 % (w/v) ammonium sulfate as the nitrogen source and initial pH 6. Specific enzyme activity at the best condition was 9.42 units / mg protein.

The ability of this strain in asparaginase activity shows that with further studies we can produce this enzyme for industrial purposes.