Influence of salts and metal nanoparticles on the activity and thermal stability of a recombinant chitinase from Stenotrophomonas maltophilia N4

Cells of Escherichia coli Rosetta, containing plasmid pET-28a with sequences of DNA of chitinase from Stenotrophomonas maltophilia N4, were used for the efficient synthesis of recombinant chitinolytic enzyme. The objective of this study was to improve thermal stability of the recombinant chitinase by salts and metal nanoparticles (NP). The studied chitinase was thermolabile and largely lost its activity in the first minutes of storage at 50 and 60 °C. The optimum temperature for colloidal chitin hydrolysis by the enzyme was 50 °C. Application of sodium aurothiomalate hydrate and manganese chloride enhanced the activity of the recombinant enzyme. In general, chitinase activity was higher when silver nanoparticles (Ag-NP) were used, but lower for other NP. The thermal stability of chitinase immobilized on Ag-NP and manganese chloride was significantly higher than that of free chitinase. Chitinase thermal stability after gold and manganese oxide nanoparticle application was higher than that of the control at 50 °C. Platinum nanoparticles had no significant effect on thermostability. The Ag-NP had a smaller diameter (from 2 to 20 nm) than Au-NP (from 5 to 70 nm) and Pt-NP (from 4 to 80 nm). The TEM analysis showed that the used NP had a higher affinity for chitinase than for the synthetic substrate. The type, size, and location of the NP on the enzyme played a major role in the thermal stability of chitinase.