Transcriptomic Analysis of Degradative Pathways for Azo Dye Acid Blue 113 in Sphingomonas melonis B-2 from the Dye Wastewater Treatment Process

Abstract

Background: Acid Blue 113 (AB113) is a typical azo dye, and the resulting wastewater is toxic and difficult to remove.

Methods: The experimental culture was set up for the biodegradation of the azo dye AB113, and the cell growth and dye decolorization were monitored. Transcriptome sequencing was performed in the presence and absence of AB113 treatment. The key pathways and enzymes involved in AB113 degradation were found through pathway analysis and enrichment software (GO, EggNog and KEGG).

Results: S. melonis B-2 achieved more than 80% decolorization within 24 h (50 and 100 mg/L dye). There was a positive relationship between cell growth and the azo dye degradation rate. The expression level of enzymes involved in benzoate and naphthalene degradation pathways (NADH quinone oxidoreductase, N-acetyltransferase and aromatic ring-hydroxylating dioxygenase) increased significantly after the treatment of AB113.

Conclusions: Benzoate and naphthalene degradation pathways were the key pathways for AB113 degradation. NADH quinone oxidoreductase, N-acetyltransferase, aromatic ring-hydroxylating dioxygenase and CYP450 were the key enzymes for AB113 degradation. This study provides evidence for the process of AB113 biodegradation at the molecular and biochemical level that will be useful in monitoring the dye wastewater treatment process at the full-scale treatment.

Keywords: Acid Blue 113; azo dye; biodegradation; decolorization; dye wastewater treatment.

Figure 1

Time course for the azo dye decolorization rates of various pure cultures and consortia of bacteria and yeasts. (a) B-1, (b) B-2, (c) B-C, (d) Y-1, (e) Y-2, (f) Y-C, and (g) T-C. The four color boxes show the sample’s color difference over four days. The legend (mg/L) represents different concentrations of the AB113 added.

Figure 2

Comparative analysis of consortium cultural growth and concomitant decolorization of the azo dye Acid Blue 113 (50 mg/L) over time. (a) B-C, (b) Y-C, and (c) T-C.

Figure 3

Time course for the FT-IR profiles of the three microbial consortia during biodegradation of the azo dye Acid Blue 113. (a) B-C, (b) Y-C, and (c) T-C.

Figure 4

(a) Scatter plot shows expression levels between comparison pairs as a scatter plot. The X—axis is control and Y—axis is the average normalized value of the DEGs group. The colored dot by volume which satisfies the |fc| ≥ 2 and independent t-test raw p-value < 0.05. (b) Multidimensional scaling comparison between control and treatment.

Figure 5

Functional categorization as (a) gene ontology (GO) and (b) EggNOG of genes differentially expressed under the azo dye Acid Blue 113 induction (treatment) condition.

Figure 6

S. melonis B-2 DEG transcriptional changes in the AB113 degradation pathway. The enzymes present in the samples were represented in green boxes, whereas the other enzymes are mentioned for reference. The enzyme reactions and the arrows in red color marked between the metabolites represent the directions of catalytic reactions. The expression patterns of control and treatment with fc > 2 values in each enzyme are shown in a heat map.