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

The preparation of γ-polyglutamic acid (γ-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 γ-PGA depolymerase was present and active extracellularly in the culture. The ywtD gene from B. subtilis NX-2, encoding the γ-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 γ-PGA degradation at a wide range of temperature (30–40 °C) and pH (5.0–8.0). On an optimal condition of 30 °C and pH 5.0, an efficient γ-PGA enzymatic degradation was achieved. The molecular weight of γ-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 γ-PGA could be available by enzymatic depolymerization.