Azoreductase activity of dye-decolorizing bacteria isolated from the human gut microbiota

Abstract

The gut microbiota enriches the human gene pool and contributes to xenobiotic metabolism. Microbial azoreductases modulate the reduction of azo-bonds, activating produgs and azo polymer-coated dosage forms, or degrading food additives. Here, we aimed to screen the healthy human gut microbiota for food colorant-reducing activity and to characterize factors modulating it. Four representative isolates from screened fecal samples were identified as E. coli (AZO-Ec), E. faecalis (AZO-Ef), E. avium (AZO-Ev) and B. cereus (AZO-Bc). Both AZO-Ef and AZO-Ev decolorized amaranth aerobically and microaerophilically while AZO-Ec and AZO-Bc had higher aerobic reduction rates. The isolates varied in their activities against different dyes, and the azo-reduction activity mostly followed zero-order reaction kinetics, with a few exceptions. Additionally, the isolates had different pH dependence, e.g., AZO-Ec was not affected by pH variation while AZO-Bc exhibited variable degradation kinetics at different pH levels. Cell-free extracts showed NADH-dependent enzymatic activities 14–19 times higher than extracellular fractions. FMN did not affect the reducing activity of AZO-Ef cell-free extract, whereas AZO-Ec, AZO-Ev and AZO-Bc had significantly higher reduction rates in its presence ( P values = 0.02, 0.0001 and 0.02, respectively). Using Degenerate primers allowed the amplification of azoreductase genes, whose sequences were 98–99% similar to genes encoding FMN-dependent-NADH azoreductases.

Ecofriendly biodegradation of Reactive Black 5 by newly isolated Sterigmatomyces halophilus SSA1575, valued for textile azo dye wastewater processing and detoxification

“…The performance of different microorganisms on the decolorization of the mixture of azo dyes was previously studied in a few reports 27 – 29 . While evaluating the decolorization of the mixtures of azo dyes by the S. halophilus strain SSA1575, it was observed that this halotolerant yeast strain was effectively decolorized mixture of azo dyes.…”

Degradation and Toxicity Analysis of a Reactive Textile Diazo Dye-Direct Red 81 by Newly Isolated Bacillus sp. DMS2

“…To understand the decolorization and degradation mechanism of DMS2, enzyme activity of azoreductase, laccase, NADH-DCIP, lignin peroxidase and tyrosinase were studied (Kurade et al, 2016;Liu, 2017). Azo-bonds of the dye were broken down via azoreductase enzymes and generate aromatic amines (Singh et al, 2015;Zahran et al, 2019). Consequently, these amines undergo further cleavage by the use of different oxidative enzymes, which finally enter into the central metabolic pathways.…”

Toxicomicrobiomics: The Human Microbiome vs. Pharmaceutical, Dietary, and Environmental Xenobiotics

“…Among azo-reducing bacteria are Clostridium, Pseudomonas, Bacillus, Geobacillus, Lysinibacillus, Enterococcus, Eubacterium, and Escherichia (Misal and Gawai, 2018). Escherichia coli, Enterococcus faecalis, Enterococcus avium, and Bacillus cereus/thuriengensis have been recently isolated from human stool samples with variable azoreduction rates (Zahran et al, 2019).…”