Characterization of Two Hydrogen Peroxide Resistant Peroxidases from Rhodococcus opacus 1CP

Selective pressure leads to an improved synthetic consortium fit for dye degradation

Microorganisms have great potential for bioremediation as they have powerful enzymes and machineries that can transform xenobiotics. The use of a microbial consortium provides more advantages in application point of view than pure cultures due to cross-feeding, adaptations, functional redundancies, and positive interactions among the organisms. In this study, we screened about 107 isolates for their ability to degrade dyes in aerobic conditions and without additional carbon source. From our screening results, we finally limited our synthetic consortium to Gordonia and Rhodococcus isolates. The synthetic consortium was trained and optimized for azo dye degradation using sequential treatment of small aromatic compounds such as phenols that act as selective pressure agents. After four rounds of optimization with different aims for each round, the consortium was able to decolorize and degrade various dyes after 48 h (80%-100% for brilliant black bn, methyl orange, and chromotrop 2b; 50-70% for orange II and reactive orange 16; 15-30% for chlorazol black e, reactive red 120, and allura red ac). Through rational approaches, we can show that treatment with phenolic compounds at micromolar dosages can significantly improve the degradation of bulky dyes and increase its substrate scope. Moreover, our selective pressure approach led to the production of various dye-degrading enzymes as azoreductase, laccase-like, and peroxidase-like activities were detected from the phenol-treated consortium. Evidence of degradation was also shown as metabolites arising from the degradation of methyl red and brilliant black bn were detected using HPLC and LC-MS analysis. Therefore, this study establishes the importance of rational and systematic screening and optimization of a consortium. Not only can this approach be applied to dye degradation, but this study also offers insights into how we can fully maximize microbial consortium activity for other applications, especially in biodegradation and biotransformation.

A mutant R70V/E166A of short manganese peroxidase showing Mn2+-independent dye decolorization

Il-MnP1, a short-type manganese peroxidase from Irpex lacteus F17, can oxidize some substrates in the absence of Mn²⁺, but the catalysis was much lower than in the presence of Mn²⁺. Here, we report a mutant R70V/E166A of Il-MnP1 with some unique properties, which possessed clearly higher catalysis for the decolorization of anthraquinone and azo dyes in the absence of Mn²⁺ than that of Il-MnP1. Importantly, the optimum pH of R70V/E166A for decolorization of anthraquinone dyes (Reactive Blue 19, RB19) was 6.5, and the mutant achieved high decolorization activities in the range of pH 4.0-7.0, whereas Il-MnP1 only showed decolorization for RB19 at pH 3.5-4.0. In addition, the optimum H₂O₂ concentration of R70V/E166A for RB19 decolorization was eight times that of Il-MnP1 and the H₂O₂ stability has improved 1.4 times compared with Il-MnP1. Furthermore, Mn²⁺ competitively inhibited the oxidation of RB19 by R70V/E166A, explaining the higher catalytic activity of the mutant R70V/E166A in the absence of Mn²⁺. Molecular docking results suggested that RB19 binds to the distal side of the heme plane in mutant R70V/E166A, which extended from the heme δ-side to the heme γ-side, and close to the mutated residues of R70V and E166A, whereas RB19 could not access the heme pocket of Il-MnP1 due to the steric hindrance of the side-chain group of Arg 70. Thus, this study constructed a useful mutant R70V/E166A and analyzed its higher Mn²⁺-independent activity, which is very important for better understanding the Mn²⁺-independent catalytic mechanism for short manganese peroxidases. KEY POINTS: • The mutant R70V/E166A of atypical MnP1 of I. lacteus F17 shows unique catalytic properties. • At pH 6.5, the R70V/E166A had a strong ability to decolorize anthraquinone dyes in the absence of Mn²⁺. • The binding sites of Reactive Blue 19 in mutant R70V/E166A were elucidated.

Microbial Degradation of Azo Dyes: Approaches and Prospects for a Hazard-Free Conversion by Microorganisms

Azo dyes have become a staple in various industries, as colors play an important role in consumer choices. However, these dyes pose various health and environmental risks. Although different wastewater treatments are available, the search for more eco-friendly options persists. Bioremediation utilizing microorganisms has been of great interest to researchers and industries, as the transition toward greener solutions has become more in demand through the years. This review tackles the health and environmental repercussions of azo dyes and its metabolites, available biological approaches to eliminate such dyes from the environment with a focus on the use of different microorganisms, enzymes that are involved in the degradation of azo dyes, and recent trends that could be applied for the treatment of azo dyes.