Alkali-treated Phragmites karka as a sustainable support for immobilized Anoxybacteroides rupiense UE27 in laccase production and azo dye detoxification.

Laccases are multi-copper oxidoreductases with broad industrial utility, however, their practical application is often limited by high production costs, low yields, and poor operational stability. Immobilizing laccase-producing bacterial cells on sustainable, cost-effective matrices, such as halophyte Phragmites karka offers a robust strategy to overcome these challenges by improving cellular stability and ensuring cell reusability for enzyme production. This study optimizes a novel immobilization system for Anoxybacteroides rupiense UE27 to achieve enhanced laccase titers and high-efficiency detoxification of carcinogenic synthetic dyes. Analysis of six factors for immobilization and laccase production through Plackett-Burman design (PBD) showed 16.45% (w/w) immobilization efficiency and 23 IU L-1 laccase. Agitation, number of matrix pieces, incubation, inoculum, and temperature were found to be significant and further optimized using a Central Composite design (CCD). Under optimized conditions, although the immobilization was 13.2%, the laccase titers increased to 37 IU L-1 in the third repeated cycle. The optimized immobilization system removed 100% and 99% of 100 ppm malachite green and congo red within 12 h of incubation, respectively. The experiment on the growth of Saccharomyces cerevisiae in presence of treated malachite green and congo red demonstrated the successful detoxification of dye solution. The mechanical analysis showed that alkaline treatment significantly increased the compression force from 46.35 N to 54.26 N and fracture strength from 983.48 kPa to 1148.29 kPa in comparison to the untreated matrix. Scanning electron microscopy further confirmed bacterial immobilization on the matrix surface. These results demonstrate the potential of Phragmites karka stem matrices as a cost-effective support matrix for bacterial laccase production.