A novel combination of immobilized Enterococcus casseliflavus sp. nov. with silver nanoparticles into a reusable matrix of Ca-Alg beads as a new strategy for biotreatment of Disperse Blue 183: Insights into metabolic characterization, biotoxicity, and mutagenic properties

Abstract

Recent advances in immobilized biologic systems for decolorizing azo dyes are gaining great attention due to microorganisms like bacteria and nanoparticles that could stimulate decolorization. Enhanced decolorization performance was observed in this study, indicating the great potential of the immobilized complex of bacterial cells and AgNPs as an alternative to the traditional biological processes to improve the performance of biological systems. The biodegradation and decolorization of Disperse Blue183 (DB 183) were investigated utilizing a novel combination of Enterococcus casseliflavus strain A2 mediated by silver nanoparticles synthesized by Marinospirillum alkaliphilum strain N in three different conditions. Ⅰ: free bacterial strain A2 (100% dye removal in 72 h), Ⅱ: immobilized bacterial strain A2 in Ca-Alg beads (100% dye removal in 15 h), and Ⅲ: immobilized bacterial strain A2 with silver nanoparticles (AgNPs) as support in Ca-Alg beads (100% dye removal in 9 h). The presence of bacterial cells and nanoparticles in Ca-Alg beads was assessed and proved by scanning electron microscope (SEM) and X-ray energy diffraction (EDX) analysis. Moreover, DB 183 and its decolorization metabolites were evaluated by applying UV–Vis, infrared spectroscopy (FTIR), and GC/MS, and the results showed that the dye was degraded. The antimicrobial effect, brine shrimp toxicity (BST) test, and mutagenicity assay in the presence and absence of metabolic activation (+S9/-S9) were run to assess DB 183 and metabolite obtained from biodegradation. The antimicrobial activity of DB 183 disappeared after treatment. Further, the results of the BST test determined that the dye has moderate biotoxicity (LC50:0.064 mg/mL), and the after-treatment product was not toxic. According to the Ames test, DB 183 had mutagenicity effect (69–84%), and the metabolic activation increased the mutagenicity of the dye) 12–25%). However, the percentage mutagenicity of decolorization products decreased, ranging from 50 to 80% without activation (-S9) and 83–96% in present activation (+S9). This work used the immobilized bacterial cells and AgNPs Ca-Alg gel beads for the first time to introduce this kind of system as a suitable technique for rapid decolorization. Using this application enables a remarkable reduction in the time dedicated to the bioremediation of dyeing wastewater.