Investigation on enzymatic degradation of γ-polyglutamic acid from Bacillus subtilis NX-2

The preparation of gamma-polyglutamic acid (gamma-PGA) from Bacillus subtilis NX-2 has been previously investigated, and its depolymerization during the batch culture was studied in this paper. The results suggested that the gamma-PGA depolymerase was present and active extracellularly in the culture. The ywtD gene from B. subtilis NX-2, encoding the gamma-PGA depolymerase was cloned and expressed in Escherichia coli. The YwtD protein was purified by metal-chelating affinity chromatography. YwtD was proved to be an endo-hydrolase enzyme and exhibited a remarkable activity in gamma-PGA degradation at a wide range of temperature (30-40 degrees C) and pH (5.0-8.0). On an optimal condition of 30 degrees C and pH 5.0, an efficient gamma-PGA enzymatic degradation was achieved. The molecular weight of gamma-PGA could be reduced within the range of 1000-20 kDa and the polydispersity also decreased as a function of depolymerization time. Therefore, a controllable degradation of gamma-PGA could be available by enzymatic depolymerization. (C) 2008 Elsevier B.V. All rights reserved.