Enzymes analysis, degradation kinetics, response surface optimization and heavy metal tolerance of the biodegradation of malachite green by Stenotrophomonas koreensis

Abstract

Stenotrophomonas koreensis, was isolated from a textile effluent and employed to biologically degrade 98.8% of the recalcitrant toxic dye malachite green in 4 h in the absence of any supplements or media. Chromatographic and Spectroscopic analysis confirmed the degradation of the dye. According to Response Surface Methodology, the optimum conditions for biodegradation were pH 6, inoculum size 6 mL (initial concentration Log₁₀CFU/mL = 6.2), and temperature 45 °C. More than 98% decolorization was achieved within 2.5 h of the addition of soymeal extract or peptone. One of the most promising features of this strain is that even in the presence of heavy metals, S. koreensis actively degraded the dye. The bacteria biodegraded malachite green following the first-order reaction kinetics. LC-MS analysis of the degradation product yielded several intermediates like Michler’s ketone (m/z 269), 4-N,N-dimethylaminophenol (m/z 137), Benzophenone (m/z 182), N,N-dimethylaniline (m/z 121), 4-(N-methylamino)-benzophenone (m/z 211), 4-aminobenzaldehyde (m/z 121), anionic canonical form of 4-aminobenzaldehyde (m/z 120), 4-(N,N-dimethylamino)benzoic acid (m/z 165), 4-(N-methylamino) benzoic acid (m/z 152). The enzymes responsible for the malachite green degradation were tyrosinase, Malachite Green reductase, and NADH-DCIP reductase. The present work is the first to report the degradation of malachite green by S. koreensis.

Keywords:

• Degradation kinetics
• degradation mechanism
• enzyme analysis
• heavy metal tolerant
• malachite green
• response surface methodology
• Stenotrophomonas koreensis

Acknowledgments

The authors extend their gratitude to Dr. Ramdhan Majhi, Senior Technical Officer, Indian Institute of Chemical Biology, Kolkata, India for the HPLC facility.

Availability of data and material

The nucleotide sequence (16S rDNA) of the concerned strain has been deposited to GenBank and the accession number hence received is MK578830. All other datasets generated and analyzed during the current study are available from the corresponding author on reasonable request.

Code availability

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Competing interests

The authors declare that they have no conflict of interest.

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Additional information

Funding

This work was supported by University Grants Commission in the form of NET-JRF fellowship to Shreya Biswas.