The effect of nitrogen concentration on laccase activity in Aspergillus niger during LDPE biodegradation

Plastic waste has accumulated tremendously over the years, and low-density polyethylene (LDPE) is one of the main contributors to overall plastic waste. This plastic waste has a detrimental effect on the environment and its inhabitants due to the slow degradation of plastic, which can take up to hundreds of years to fully degrade naturally in the environment. Aspergillus niger is a filamentous fungus that can produce extracellular enzymes such as laccase that can break down LDPE and is therefore proposed as a tool for mycoremediation. The activity of laccase is highly influenced by the availability of nitrogen in the media; however, the influence of the nitrogen concentration on A. niger’s laccase during the process of LDPE degradation is unknown. This study aims to investigate the activity of laccase under varied concentrations of nitrogen. The nitrogen source used in this experiment is ammonium nitrate, ranging from 1 g/L to 5 g/L. The laccase assay performed was carried out using the guaiacol protocol. The A. niger was inoculated for 4 weeks in BHB media where LDPE resins were added as the only source of carbon. The concentration with the highest laccase activity was 2 g/L at 0.01796 IU on Day 15, while the lowest enzymatic activity was exhibited by 6 g/L at 0.00012 IU on Day 5. The results conclude that laccase performs optimally under the limited nitrogen concentration in the range of 2-5 g/L. A limitation of this study is that the effect of laccase on the LDPE plastic resins could not be studied due to the short duration of the experiment.