Decolorization of malachite green by free and immobilized Pseudomonas sp. strain C2-4

Malachite green, a carcinogenic triphenylmethane dye. In this study, Pseudomonas sp. C2-4 was isolated, and both free and immobilized forms of this bacterium demonstrated high decolorization capacity. The free cells were able to remove 100 mg/L and 1000 mg/L of malachite green within 48 h, achieving efficiencies of 99.68% ± 0.26 and 85.32% ± 2.00, respectively, and maintained over 90.12% ± 3.15 efficiency between 28 and 40 °C and pH 6.0-10.0. After immobilization, the strain exhibited enhanced environmental adaptability, achieving over 87% efficiency under broader conditions (15-45 °C, pH 3.0-10.0, 1-5% NaCl) and retaining 94.57% ± 1.60 efficiency after five reuse cycles. Among metal ions, Ca²⁺ promoted degradation, Cu²⁺ strongly inhibited it, while Mn²⁺, Mg²⁺, and Zn²⁺ showed negligible effects. Mechanism studies via Fourier Transform Infrared Spectroscopy and Gas Chromatography-Mass Spectrometry indicated that malachite green was removed through both biosorption (involving functional groups such as aliphatic nitro compounds, methyl C-H, carboxyl, and aromatic ethers) and biodegradation (yielding N, N-dimethylaniline, aniline, and benzoic acid). Phytotoxicity tests following treatment with either free or immobilized strain C2-4 confirmed effective detoxification, as evidenced by significant increase in Chinese cabbage seed germination rates, root length, and stem length. These results demonstrate the strain's exceptional decolorization and detoxification capabilities via both biosorption and biodegradation, with immobilization enhancing its effectiveness for treating dye-contaminated wastewater under diverse conditions, highlighting its significant potential for practical application.