Impact of redox-mediators in the degradation of olsalazine by marine-derived fungus, Aspergillus aculeatus strain bpo2: Response surface methodology, laccase stability and kinetics

Abstract

The indiscriminate disposal of olsalazine in the environment poses a threat to human health and natural ecosystems because of its cytotoxic and genotoxic nature. In the present study, degradation efficiency of olsalazine by the marine-derived fungus, Aspergillus aculeatus (MT492456) was investigated. Optimization of physicochemical parameters (pH. Temperature, Dry weight) and redox mediators {(2,20-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS), p-Coumaric acid and 1-hydroxybenzotriazole (HOBT)} was achieved with Response Surface Methodology (RSM)-Box-Behnken Design (BBD) resulting in 89.43% removal of olsalazine on 7th day. The second-order polynomial regression model was found to be statistically significant, adequate and fit with p < 0.0001, F value=41.87 and correlation coefficient (R2=0.9826). Biotransformation was enhanced in the redox mediator-laccase systems resulting in 99.5% degradation of olsalazine. The efficiency of ABTS in the removal of olsalazine was more pronounced than HOBT and p-Coumaric acid in the laccase-mediator system. This is attributed to the potent nature of the electron transfer mechanism deployed during oxidation of olsalazine. The pseudo-second-order kinetics revealed that the average half-life (t1/2) and removal rates (k1) increases with increasing concentrations of olsalazine. Michaelis-Menten kinetics affirmed the interaction between laccase and olsalazine under optimized conditions with maximum removal rate, Vmax=111.11 hr-1 and half-saturation constant, Km=1537 mg L-1. At the highest drug concentration (2 mM); 98%, 95% and 93% laccase was remarkably stabilized in the enzyme-drug degradation system by HOBT, ABTS and p-Coumaric acid respectively. This study further revealed that the deactivation of laccase by the redox mediators is adequately compensated with enhanced removal of olsalazine.