Abstract

Eight bacterial strains showing aspartase activity were isolated from the semi-arid soil samples of the Laguna region of North-East Mexico, using a selective culture medium with ammonium fumarate as an inducer for the production of aspartase. The enzyme activity of the strains was determined by the consumption of ammonium fumarate 0.5 M, pH 8.0 and 37°C. From the eight strains, ASP1 and ASP3 strains showed the highest specific enzyme activity (U/mg of protein), and were used for further studies and their molecular characterization. The production of aspartic acid by these strains was confirmed by paper chromatographic analysis. In order to identify the bacterial strains, primers specific to aspartase were used to amplify a conserved region of 430 bp. The amplicons were sequenced by the Sanger method and ASP3 and ASP1 strains were identified as Acinetobacter calcoaceticus PHEA-2 by BLAST search.

INTRODUCTION

There is a great demand for amino acids by various industries and nearly half of the global production of amino acids is used in the food industry, where L-glutamic acid, L-aspartic acid and L-phenylalanine are considered of great importance (1, 2). Various methods such as extraction, chemical synthesis, fermentation or enzymatic synthesis are used for the production of amino acids. The use of microorganisms in a fermentation process for producing amino acids using economical sources of carbon is becoming a profitable process (3), apart from various other advantages such as simplification of the process, decrease the cost of raw materials, energy, easy separation of the product, waste reduction and recycle of enzyme for various production cycles (4). In actual, amino acid L-aspartic acid, is produced on a large scale by means of the enzyme aspartase and is widely used for the elaboration of aspartame (5). Aspartase or aspartate ammonia lyase (EC 4.3.1.1.) is associated with cell protein complex (6) and also can catalyze the reversible deamination of amino acid L-aspartic to fumarate (7), and hence both the L-aspartic acid and fumarate can fu ...