Microbial Decolorization of Crystal Violet Dye by a Native Multi-Metal Tolerant <i>Aeromonas caviae</i> MT-1 Isolate from Dye-Contaminated Soil: Optimization and Phytotoxicity Study

In the recent past, one of the main environmental issues is the contamination of textile dye wastes. The toxicity of dyes poses adverse effects on the flora and fauna of the ecosystem. The present study aimed to isolate bacteria that decolourize crystal violet dye, optimization of various environmental factors for effective decolourization, and phytotoxicity analysis. Out of 13 isolated bacteria, a single isolate was able to grow at 250 mg/L crystal violet dye concentration in a synthetic medium and identified as Aeromonas caviae MT-1 strain (accession number; LC720408) using morphological, biochemical and molecular analyses. Presumably, this is the first report of crystal violet dye decolourization by a native Aeromonas caviae isolate. In this study, after a 72-hour incubation period, a maximum of 98.0% dye decolourization was observed at neutral pH and 35°C with 5% v/v bacterial culture under static culture conditions. Dye decolourization was inhibited to a significant degree by the rising of its concentration. UV-Vis spectra analysis of samples before and after decolourization showed the possible degradation of crystal violet dye by A. caviae. The strain MT-1 was also tolerant to toxic heavy metals like arsenic, lead, and chromium. Phytotoxicity tests revealed that decolourized dye products inhibited Vigna radiata growth less than the un-decolourized dye solution. The findings revealed that a native multi-metal tolerant A. caviae MT-1 isolate could decolourize crystal violet dye rapidly, and possibly have the ability for extensive treatment of dyecontaminated waste.