Evaluation of Lead (Pb) Effects on Laccase Enzyme Activity in Bacillus Subtilis WPI

Aim and objectives: Lead is one of the most important environmental pollutants that plays a significant role in increasing the stability of some other pollutants through changing the microbial profile of soil.  Bacillus subtilis WPI is one of the most abundant bacteria existing in the wastewater. Due to the presence of laccase enzyme in this bacterium, it can facilitate the decomposition process of aromatic pollutants in wastewaters. This study aimed to investigate the effect of different concentrations of lead on the growth and biological activity of laccase enzyme in B. subtilis WPI. Material and Methods: After purification of bacteria, the growth trend of B. subtilis WPI, along with the activity of laccase enzyme in different concentrations of lead was investigated based on kinetic method. Results: In this study, the bacterial growth at lead concentration of 400 mg/L was reduced in a dose-dependent manner, which this decrease was significant at concentrations of 300 and 400 mg/L (p <0.001). The level of laccase enzyme activity in the lead concentration range 20-160 mg/L was also reduced in a dose-dependent manner, which implied that the highest decrease was observed at lead concentration of 160 mg/L (p <0.01). Conclusion: In general, our findings showed that there was no significant change in bacterial growth in the lead concentration range 20-200 mg/L, while a significant change was found in the activity of laccase enzyme in the mentioned concentration range. Therefore, it seems that this reduction in enzyme activity can indirectly increase the stability of aromatic oil pollutants in the environment.