Eco-friendly azo dye removal via a robust laccase from Acinetobacter baumannii KMSP005: a thermo-alkaliphilic...

The enzymatic breakdown of synthetic azo dyes is a potential and environmentally acceptable way to remove harmful contaminants commonly produced by the textile and dye industries. In this study, laccase-producing bacteria were isolated from soil samples collected from the Eastern Himalayan region and molecularly identified as Acinetobacter baumannii KMSP005 by 16S rDNA gene sequencing. The primary objective was to optimise laccase production using response surface methodology, while a secondary objective was to evaluate the efficiency of the bacterial laccase in degrading azo dye methyl red. Under optimised conditions, ~ 96% degradation of methyl red was achieved within 18 h, with a maximum laccase activity of 3.49 IU mL⁻1. Using coconut husk, a cheap agricultural waste, as a substrate for laccase production produced an impressive enzyme activity of 4.9 IU mL⁻1. When using agro-waste, laccase production increased by about 1.40-fold. Analysis of the breakdown products using gas chromatography-mass spectrometry revealed that methyl red was changed into simpler, less toxic, mediational compounds, proving the process' effectiveness and environmental safety. The maximal activity of 2.25 IU mL⁻1 at 50 °C and 2.50 IU mL⁻1 at pH 9 demonstrated the thermostable and alkali-tolerant characteristics of this laccase. The laccase exhibited thermo-alkaliphilic stability, retaining 82.05% of its initial activity at 50 °C and 86.66% activity at pH 9.