Biodegradation of Reactive Red-111 by a novel multi-enzyme producing bacterial consortium: optimization through RSM and kinetics study

Abstract

This study presents the efficient biodegradation of synthetic dye Reactive Red-111 (RR-111) using a newly developed multi-enzyme producing bacterial consortium comprising of Lysinibacillus boronitolerans, Lysinibacillus macroides, Brevundimonas diminuta and Acinetobacter indicus. Radar plot-based enzymatic profiling revealed a significant upregulation of multiple enzymes within the bacterial consortium. The consortium demonstrated synergistic enzymatic action of laccase, Mn peroxidase, azoreductase and lignin peroxidase leading to rapid dye degradation of 95.64% and greatest COD removal of 90.63% within 48 h. The percentage of dye decolorization and COD removal was evaluated using Response Surface Methodology (RSM) with a Box-Behnken Design (BBD) that assesses the combined impacts of key process variables. The RSM approach was used to identify the best combinations of important process variables as dye concentration (50–500 mg/L), pH (5–10) and incubation temperature (30-45 °C). Analysis of variance (ANOVA) was used to confirm the suitability of model where second-order polynomial model was fitted to the experimental data. Regression analysis revealed the experimental data was good fit with a coefficient of determination R. squared of 0.9967, Adj. R-Squared of 0.9940 and a predicted R. squared of 0.9674. The model exhibited non-significant Lack of fit. The optimal parameters for decolorization were determined to be 200 mg/L dye concentration, pH 7 and incubation temperature of 37 °C. The correlation between dye concentration and the rate of decolorization was evaluated using Michaelis-Menten kinetic modeling. The non-linear regression analysis revealed maximum decolorization rate Vmax = 39.92 mg/L/h and half saturation constant Km = 129.88 mg/L. The reliability of these outcomes with Lineweaver Burk plot confirmed the suitability of Michaelis-Menten model. The biodegradation of RR-111 dye was characterized using GC-MS, FTIR and UV-Visible spectroscopic analysis.