Enzymatic biodegradation, kinetic study, and detoxification of Reactive Red-195 by <i>Halomonas meridiana</i> isolated from Marine Sediments of Andaman Sea, India

Azo dyes are a significant class of hazardous chemicals that are extensively utilised in diverse industries. Industries that manufacture and consume reactive azo dyes generate hyper-saline wastewater. The ability of halotolerant bacteria to thrive under extreme environmental conditions thus makes them a potential candidate for reactive azo dye degradation. An efficient halotolerant bacterium (isolate SAIBP-6) with the capability to degrade 87.15% of azo dye Reactive Red 195 (RR-195) was isolated from sea sediment and identified as <i>Halomonas meridiana</i> SAIBP-6. Strain SAIBP-6 maintained potential decolourisation under a wide range of environmental conditions viz. 35–45°C temperature, 50–450 mg/L RR-195, pH 7–9, and 50–150 g/L NaCl. However, maximum decolourisation occurred at 40°C, 200 mg/L RR-195 dye, pH 9, and 50 g/L NaCl, under static conditions. Tyrosinase and azoreductase were responsible for dye degradation. The reaction catalysed by these enzymes followed zero-order kinetics. The maximum velocity (Vmax) of the enzymatic reaction was 4.221 mg/(L.h) and the Michaelis constant (Km) was 517.982 mg/L. Strain SAIBP-6 also efficiently decolourised Reactive Black-5 and Reactive Yellow-160 dye. The biodegradation process was further studied with the help of UV–Vis spectral scan, ultra-high performance liquid chromatography (UPLC), fourier-transform infra-red spectroscopy (FT–IR), and proton nuclear magnetic resonance (¹H NMR) analysis. Finally, cytogenotoxicity assay conducted with the meristematic root tip cells of <i>Allium cepa</i> and phytotoxicity assay conducted with the seeds of <i>Vigna mungo</i> led to the inference that strain SAIBP-6 significantly reduced the toxicity of RR-195 after biodegradation.