Degradation of malachite green by a novel salt-tolerant Vibrio natriegens: Optimal degradation conditions, mechanisms, and safety assessment

Abstract

Synthetic dyes, such as malachite green (MG), are widely used in the textile industry but pose significant environmental risks due to their toxicity. In this study, a highly efficient salt-tolerant bacterial strain, Vibrio natriegens SWS5, was isolated and identified through morphological, physiological, biochemical, and 16S rRNA gene sequence analyses. Systematic investigations were conducted to optimize degradation conditions, analyze enzyme activities, elucidate degradation pathways, and assess detoxification effects. The optimal degradation conditions were determined as follows: peptone 7.5 g/L, NaCl 20 g/L, Fe²⁺ 0.04 g/L, pH 7, temperature 30 °C, and shaking speed 220 rpm. Under these conditions, SWS5 achieved 97.88 % degradation of MG (100 mg/L) within 168 hours. After MG added, enzyme activity assays revealed in dye-decolorizing peroxidase (823 U/L), laccase (358 U/L), and manganese peroxidase (0.204 U/L) activities. HPLC-MS analysis identified key intermediates, enabling the proposal of two potential MG degradation pathways. Toxicity assessments using microbial tests and zebrafish models demonstrated a significant reduction in the toxicity of degradation products. Transcriptome sequencing provided novel insights into the regulatory pathways of MG degradation, offering a theoretical foundation for the bioremediation of MG contaminated wastewater. Vibrio natriegens was demonstrated for the first time to degrade triphenylmethane dyes, especially MG, in high-salinity environments. This study highlights the potential of Vibrio natriegens SWS5 as an efficient and eco-friendly solution for dye wastewater treatment.