Decolorization of methyl orange and aniline red dyes by Enterococcus hirae isolated from beach sand

Azo dyes are categorized as toxigenic colorants, and the untreated discharge of effluents containing these compounds poses serious risks to both the environment and human health. Therefore, the objective of this study was to isolate and characterize an Enterococcus hirae Alf123 strain, obtained from beach sand, with the ability to degrade the azo dyes methyl orange and aniline red, to evaluate its decolorization capacity, and to propose a possible degradation pathway for both dyes. The bacterial strain was isolated from beach sand samples using selective culture media, and its identity was confirmed through biochemical tests, tuf gene amplification, and 16S rRNA gene sequencing. Decolorization assays were carried out using various dye concentrations. In addition, the activity of several enzymes laccases, lignin peroxidase, manganese peroxidase, and dioxygenases was evaluated, and spectroscopic analyses (UV-Vis and FT-IR) were employed to monitor structural changes in the dyes during degradation. The Alf123 strain achieved complete decolorization of methyl orange and aniline red at concentrations up to 200 mg/L and maintained activity at concentrations as high as 500 mg/L. Lignin peroxidase was the most efficient enzyme, reaching decolorization rates of 47.43% for methyl orange and 33.98% for aniline red, followed by manganese peroxidase with rates of 27.38% and 20.02%, respectively. Based on experimental results and literature review, a possible degradation mechanism and metabolic pathway used by E. hirae Alf123 strain for both dyes were proposed.