Glucoamylase from a thermophilic strain of Bacillus licheniformis RT-17: production and characterization

摘要

Glucoamylase is an industrially important enzyme that finds many applications including in the production of glucose and fructose syrups. Commercially it is obtained from the species of Aspergillus and Bacillus. Bacillus being source of thermostable enzymes has been studied widely for the prospects of getting proteins having industrially relevant properties. In the present study, a thermophilic strain of Bacillus licheniformis RT-17 was investigated for its ability to produce glucoamylase. After initial experiments, the factors affecting glucoamylase production were screened using Plackett-Burman design (PBD). The data indicated that out of six factors, one factor i.e. incubation period was found having significant effect on the response and hence was studied separately. The strain produced the maximum titers (0.017 IU mL -1 ) after 24 h of incubation, the production dropped significantly if cultivation is extended to 48 or 72 h that could be linked with the proteolytic potential of this strain. The enzyme in cell-free culture supernatant was partially purified by 1.3 fold with 65% yield using 80% ammonium sulphate. The partially purified enzyme was characterized for its temperature and pH optima. The results showed that glucoamylase from RT-17 performed optimally at 50 o C under alkaline conditions (pH 8.2) in presence of 1.8% starch. Thermophilic nature of the strain, heat- and alkali-stability of the glucoamylase indicate possible candidature of the strain for future biotechnological applications.