Stimulating effect of nanoparticles and salts on thermo and halo-tolerant cell-bonded laccase synthesis in Acinetobacter sp. UIETPU

Laccase synthesizing Acinetobacter sp. UIETPU was isolated from the rhizosphere of the paddy plant. Enzyme was firmly cell attached and no extracellular laccase activity was detected up to 96h, 37 degrees C, and 150 rpm. Nanoparticles (NPs) of Cu and CuO (100 mu M) increased the cell-bonded laccase synthesis by 2.1 and 2.3 fold respectively, but potent laccase inducer CuSO4 enhanced the enzyme production by 1.5 fold at the same concentration. There was no adverse effect of NaCl (0.5-5.0%) on laccase synthesis when added to the production media. Enzyme oxidizes the syringaldazine and 2, 6-dimethoxyphenol (specific substrates of laccase) and inhibited by the dithiothreitol (DTT), sodium azide and cystein by 98, 65 and 52% respectively. Cell-bonded laccase showed the 100% activity up to 2h and t1/2 of the bonded enzyme was 4h at 80 degrees C. Field emission scanning electron microscopy (FESEM) revealed that there was no lysis of Acinetobacter sp. UIETPU cells in the presence of CuO NPs.