Mineralization of aromatic amines liberated during the degradation of a sulfonated textile colorant using Klebsiella pneumoniae strain AHM
Introduction
Textile industry generates voluminous colored effluents comprising distinct classes of dye and their presence would contribute to the aesthetically impaired effect into the environment. Besides, these dyes exhibit high toxicity and carcinogenicity to the aquatic and terrestrial ecosystem. Thus, there is a demand for the treatment strategy, which eliminates the color with the simultaneous reduction in toxicity prior discharging [1]. The reactive sulfonated azo dyes, despite being a recalcitrant compound, they are being widely used. The anaerobic reductive cleavage of azo dyes releases the toxic aromatic amines like sulphonated benzene or naphthalene derivatives with lower biodegradability [2]. But for achieving complete mineralization, the aerobic decolorization and detoxification of sulphonated azo dyes are employed [3].
The biodegradation of the sulfonated aromatic compounds is very difficult as they are hydrophilic and are impermeable through the bacterial cell membrane, making them as a persistent recalcitrant compound [4]. The nitro-substituted sulfonates in the benzene ring are highly persistent than the unsubstituted sulfonates [5]. The conventional physicochemical treatment techniques are inefficient as they fail to eliminate toxicity and have high running cost [6], [7]. Bioremediation of the dyeing wastewater using the bacterial cells has gained widespread attention due to their ability to ameliorate faster degradation and mineralization by inducing oxidoreductases [8], [9].
The present study emphasizes on the feasibility of employing K. pneumoniae strain AHM, an isolated and acclimated cell in detoxifying the sulfonated textile dye; RO16. Also for the first time, we have proposed an equation to estimate the mineralization rate of aromatic amines liberated during the biotransformation. The spectrophotometric, spectroscopic and chromatographic techniques were used to reveal the mechanism of RO16 biotransformation. Conclusively, phytotoxic assessments were made to compare between the toxicity of RO16 and biotransformed products.
Section snippets
Chemicals
RO16 or Orange 3R (C20H17N3Na2O11S3, molecular weight, MW = 617.54, maximum wavelength, λmax = 413 nm and molecular structure is given in Supplementary Materials Fig. S1), ABTS (2,2ʹ–azino–bis(3–ethyl–benzothiazoline–6 sulfonic acid)) and p-chloranil were purchased from Sigma-Aldrich (Bangalore, India). Double distilled water was used for preparing RO16 solutions throughout the study, and the stock solution of RO16 was stored in the dark at room temperature. The nutrient broth and agar were from
Screening and acclimation of RO16 biotransforming strain
The sulfonated azo dyes are impermeable through the bacterial cell membrane and thus, the isolation of bacterium capable of cleaving the sulfonated compounds by the oxidoreductases are of great interest [4]. In our investigation, an indigenous bacterium was screened from the soil collected from textile industry contaminated soil. The bacterial cell was acclimated which made the cells to adopt an alternate metabolic pathway to utilize 250 mg/L RO16, for their survival in the absence of glucose.
Conclusions
The ability of an indigenous bacterium; K. pneumoniae strain AHM dwelling in the textile effluent contaminated sites was tested to biotransform RO16 with concomitant mineralization. The analytical techniques along with the activities of the oxidoreductases elucidated that RO16 got biotransformed into different products with few of them were found to be bio-actives. The equation for quantifying the mineralization would be a reliable mean to quantify the efficacy of the wastewater treatment in
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