Exploring the decolorization efficiency and biodegradation mechanisms of different functional textile azo dyes by Streptomyces albidoflavus 3MGH

Abstract

Efficiently mitigating and managing environmental pollution caused by the improper disposal of dyes and effluents from the textile industry is of great importance. This study evaluated the effectiveness of Streptomyces albidoflavus 3MGH in decolorizing and degrading three different azo dyes, namely Reactive Orange 122 (RO 122), Direct Blue 15 (DB 15), and Direct Black 38 (DB 38). Various analytical techniques, such as Fourier Transform Infrared (FTIR) spectroscopy, High-Performance Liquid Chromatography (HPLC), and Gas Chromatography-Mass Spectrometry (GC-MS) were used to analyze the degraded byproducts of the dyes. S. albidoflavus 3MGH demonstrated a strong capability to decolorize RO 122, DB 15, and DB 38, achieving up to 60.74%, 61.38%, and 53.43% decolorization within 5 days at a concentration of 0.3 g/L, respectively. The optimal conditions for the maximum decolorization of these azo dyes were found to be a temperature of 35 °C, a pH of 6, sucrose as a carbon source, and beef extract as a nitrogen source. Additionally, after optimization of the decolorization process, treatment with S. albidoflavus 3MGH resulted in significant reductions of 94.4%, 86.3%, and 68.2% in the total organic carbon of RO 122, DB 15, and DB 38, respectively. After the treatment process, we found the specific activity of the laccase enzyme, one of the mediating enzymes of the degradation mechanism, to be 5.96 U/mg. FT-IR spectroscopy analysis of the degraded metabolites showed specific changes and shifts in peaks compared to the control samples. GC-MS analysis revealed the presence of metabolites such as benzene, biphenyl, and naphthalene derivatives. Overall, this study demonstrated the potential of S. albidoflavus 3MGH for the effective decolorization and degradation of different azo dyes. The findings were validated through various analytical techniques, shedding light on the biodegradation mechanism employed by this strain.

Keywords: Streptomyces; Azo dyes; Biodegradation; Decolorization; GC-MS; HPLC.

Fig. 1

Morphological and molecular identification of isolate A7 showing cultural view (A), flexuous sporephores hyphae (B), and Transmission electron microscope (TEM) photomicrograph showing smooth spore surface (C). Molecular phylogenetic analyses of S. albidoflavus 3MGH (D) by Maximum Likelihood Model of MEGA 7.0 package

Fig. 2

Effect of different incubation temperatures (A), pH of the culture medium (B), Incubation time (C), Dye concentration (D) different carbon sources (E), different nitrogen sources (F) on RO 122, DB 15, and DB 38 azo dyes by S. albidoflavus 3MGH. different letters are significantly different at P < 0.05 according to Tukey’s test

Fig. 3

FT-IR spectra and photographic images of A mono azo dye (Reactive Orange 122), B di azo dye (Direct Blue 15) and C tri azo dye (Direct Black 38) before and after incubation with S. albidoflavus 3MGH at optimum conditions

Fig. 4

Scheme for the proposed mechanism for degradation process of mono azo dye (reactive orange 122) through reductive cleavage of azo bonds by the action of S. albidoflavus 3MGH under optimum condition

Fig. 5

Scheme for the proposed mechanism for degradation process of di azo dye (DB 15) through reductive cleavage of azo bonds by the action of S. albidoflavus 3MGH under optimum condition

Fig. 6

Scheme for the proposed mechanism for degradation process of tri azo dye (DB 38) through reductive cleavage of azo bonds by the action of S. albidoflavus 3MGH under optimum condition