Isolation and Characterization of Gram-Negative Bacterial Strains for Biodegradation of Crystal Violet and Safranin from Textile Sources

The extensive use of synthetic dyes in textile industries has led to severe environmental pollution, particularly in developing regions such as South Asia, where inadequate wastewater management persists. Crystal Violet (CV) and Safranin (SF), belonging to the triphenylmethane and phenazine dye groups respectively, are highly stable, toxic, and resistant to conventional treatment methods. This study aimed to isolate, identify, and characterize Gram-negative bacterial strains from textile effluent capable of degrading these dyes efficiently. Wastewater samples collected from Maksons Spinning Mill (Ashulia, Savar, Dhaka, Bangladesh) were serially diluted and cultured on MacConkey agar for bacterial isolation. Four distinct Gram-negative bacterial species—Comamonas terrae, Burkholderiales bacterium, Citrobacter sp., and Acinetobacter baumannii—were identified based on biochemical assays and confirmed through 16S rRNA gene sequencing, with identities ranging between 96.7% and 98.8%. Decolorization assays were conducted using 200 ppm dye concentrations under controlled incubation conditions, and the decolorization efficiency was quantified spectrophotometrically at 590 nm (CV) and 520 nm (SF). Results demonstrated strain-specific dye degradation capabilities: Comamonas terrae exhibited the highest CV degradation (78.2% within 24 h), followed by Burkholderiales sp. (70.1%), Citrobacter sp. (56.3%), and A. baumannii (48.8%). Conversely, A. baumannii displayed superior activity against SF (45.93%), outperforming the other isolates. Interestingly, the bacterial consortium showed moderate synergistic efficiency, achieving 34.5% CV and 54.2% SF degradation after 24 h, suggesting potential metabolic competition among the isolates. Overall, this research provides a promising microbial approach to eco-friendly, cost-effective textile dye wastewater treatment, with implications for sustainable industrial effluent management in resource-constrained regions.