Decolorization of the benzidine-based azo dye Congo red by the new strain Shewanella xiamenensis G5-03

Shewanella xiamenensis G5-03 was observed to decolorize the azo dye Congo red in synthetic wastewater. The influence of some factors on the dye decolorization efficiency was evaluated. The optimal decolorization conditions were temperature 30-35 °C, pH 10.0, incubation time 10 h, and static condition. The kinetic of Congo red decolorization fitted to the Michaelis–Menten model (Vmax = 111.11 mg L-1 h-1 and Km = 448.3 mg L-1). The bacterium was also able to degrade benzidine, a product of azo bond breakage of the Congo red, which contributed to reduce the phytotoxicity. The ability of S. xiamenensis G5-03 for simultaneous decolorization and degradation of Congo red shows its potential application for the biological treatment of wastewaters containing azo dyes.

Design and Engineering of an Efficient Peroxidase Using Myoglobin for Dye Decolorization and Lignin Bioconversion

The treatment of environmental pollutants such as synthetic dyes and lignin has received much attention, especially for biotechnological treatments using both native and artificial metalloenzymes. In this study, we designed and engineered an efficient peroxidase using the O2 carrier myoglobin (Mb) as a protein scaffold by four mutations (F43Y/T67R/P88W/F138W), which combines the key structural features of natural peroxidases such as the presence of a conserved His-Arg pair and Tyr/Trp residues close to the heme active center. Kinetic studies revealed that the quadruple mutant exhibits considerably enhanced peroxidase activity, with the catalytic efficiency (kcat/Km) comparable to that of the most efficient natural enzyme, horseradish peroxidase (HRP). Moreover, the designed enzyme can effectively decolorize a variety of synthetic organic dyes and catalyze the bioconversion of lignin, such as Kraft lignin and a model compound, guaiacylglycerol-β-guaiacyl ether (GGE). As analyzed by HPLC and ESI-MS, we identified several bioconversion products of GGE, as produced via bond cleavage followed by dimerization or trimerization, which illustrates the mechanism for lignin bioconversion. This study indicates that the designed enzyme could be exploited for the decolorization of textile wastewater contaminated with various dyes, as well as for the bioconversion of lignin to produce more value-added products.

Biodegradation of Basic Yellow Auramine- O Dye using Staphylococcus sp. Isolated from Textile Industry Effluent

Due to the increased use of synthetic dyes in various industries, there is an increased disposal of wastewater containing harmful dyes. These, in turn, have affected plants, animals, and humans. The physical and chemical methods of dye decolorization have failed to degrade the synthetic dyes in industrial effluents completely. The microbial decolorization is better due to its versatility, dynamic metabolism, and potential machinery of enzymes. This study aimed to degrade basic yellow dye auramine O by bacteria isolated from textile industry effluent. In this regard, five bacterial strains were isolated and screened from a soil sample taken from textile industry effluent. The initial physical and biochemical characterization of the bacterial isolates 1 and 2 indicated catalase test-positive, starch test-negative, motility agar test-negative, gram staining test-positive, and morphology-bacillus. The bacterial isolates 3, 4, and 5 indicated oxidase test-negative, urease test-positive, gram staining test-negative, and morphology-staphylococcus. All the isolates were further subjected to a screening test, where isolate 5 showed maximum dye decolorization of 98.9% in 96 h. The biodegradation of dye was optimized for different values of initial pH (4-10), inoculum size (2% -10%), initial dye concentration (50 mgL-1 to400 mgL-1), carbon source (glucose, fructose, xylose, starch and lactose) and nitrogen source (peptone, ammonium sulphate, yeast extract, ammonium nitrate and urea). Maximum dye decolorization was observed for initial dye concentration of 200 mgL-1, initial pH of 6, inoculum size of 10%, yeast extract as nitrogen source, and glucose as carbon source. Therefore, dye degradation by bacteria can be used as a potential method for auramine O dye treatment.

Wood-feeding termite gut symbionts as an obscure yet promising source of novel manganese peroxidase-producing oleaginous yeasts intended for azo dye decolorization and biodiesel production

Background The ability of oxidative enzyme-producing micro-organisms to efficiently valorize organic pollutants is critical in this context. Yeasts are promising enzyme producers with potential applications in waste management, while lipid accumulation offers significant bioenergy production opportunities. The aim of this study was to explore manganese peroxidase-producing oleaginous yeasts inhabiting the guts of wood-feeding termites for azo dye decolorization, tolerating lignocellulose degradation inhibitors, and biodiesel production. Results Out of 38 yeast isolates screened from wood-feeding termite gut symbionts, nine isolates exhibited high levels of extracellular manganese peroxidase (MnP) activity ranged between 23 and 27 U/mL after 5 days of incubation in an optimal substrate. Of these MnP-producing yeasts, four strains had lipid accumulation greater than 20% (oleaginous nature), with Meyerozyma caribbica SSA1654 having the highest lipid content (47.25%, w/w). In terms of tolerance to lignocellulose degradation inhibitors, the four MnP-producing oleaginous yeast strains could grow in the presence of furfural, 5-hydroxymethyl furfural, acetic acid, vanillin, and formic acid in the tested range. M. caribbica SSA1654 showed the highest tolerance to furfural (1.0 g/L), 5-hydroxymethyl furfural (2.5 g/L) and vanillin (2.0 g/L). Furthermore, M. caribbica SSA1654 could grow in the presence of 2.5 g/L acetic acid but grew moderately. Furfural and formic acid had a significant inhibitory effect on lipid accumulation by M. caribbica SSA1654, compared to the other lignocellulose degradation inhibitors tested. On the other hand, a new MnP-producing oleaginous yeast consortium designated as NYC-1 was constructed. This consortium demonstrated effective decolorization of all individual azo dyes tested within 24 h, up to a dye concentration of 250 mg/L. The NYC-1 consortium's decolorization performance against Acid Orange 7 (AO7) was investigated under the influence of several parameters, such as temperature, pH, salt concentration, and co-substrates (e.g., carbon, nitrogen, or agricultural wastes). The main physicochemical properties of biodiesel produced by AO7-degraded NYC-1 consortium were estimated and the results were compared to those obtained from international standards. Conclusion The findings of this study open up a new avenue for using peroxidase-producing oleaginous yeasts inhabiting wood-feeding termite gut symbionts, which hold great promise for the remediation of recalcitrant azo dye wastewater and lignocellulosic biomass for biofuel production. Graphical Abstract

Influence of Temperature in Degradation of Organic Pollution Using Corona Discharge Plasma

Dye solution temperature influences the elimination efficiency of water-soluble and anionic acid dye. Acid Blue 25 dye, using a gas–liquid electrical discharge system, was successfully investigated. The results showed an increase in the percentage of dye decolorization from 91.16% to 96.12% when the dye solution temperature was increased from 278 K to 308 K. However, the initial dye decolorization percentage was decreased with the further increase in dye solution temperature from 318 K to 358 K. The 2D simulation model was introduced to consider the influence of temperature and the electric field generated by corona discharge plasma in air and water. Results also showed a great match between the experimental and the simulation results. The reaction rates of dye degradation were analyzed using the Arrhenius equation. Furthermore, pseudo-zero-, pseudo-first-, and pseudo-second-order models were used to determine the reaction kinetics. The best fit for the experimental data would follow the pseudo-first-order model. Finally, electrical energy per order, energy yield, and experimental degradation data were calculated to investigate the cost analysis.

Modified Composite Based on Magnetite and Polyvinyl Alcohol: Synthesis, Characterization, and Degradation Studies of the Methyl Orange Dye from Synthetic Wastewater

The goal of the present paper was to synthesize, characterize, and evaluate the performance of the modified composite based on magnetite (Fe3O4) and polyvinyl alcohol (PVA). The obtained composite was used to degrade Methyl Orange dye from synthetic wastewater by a laboratory photocatalytic reactor. Various parameters of the photodegradation process were tested: composite dosage, amount of hydrogen peroxide (H2O2), and pH. The composite was characterized by Fourier Transform Infrared (FTIR) Spectroscopy, X-ray Diffraction (XRD), and Scanning Electron Microscopy (SEM). The degradation experiments indicated that the complete dye decolorization depended on the amount of H2O2. In addition, the H2O2 could accelerate Methyl Orange degradation to more highly oxidized intermediates in the presence of UV light (99.35%). The results suggested that the obtained modified composite could be used to treat wastewater containing various types of dyes.

Bacillus subtilis with a 1% population enhances the activity of Enterococcus faecalis with a 99% population

Microbes are present as communities in the environment. However, the importance of minor populations has not been well studied experimentally. In this study, we evaluated the role of Bacillus subtilis with a 1% population and its effect on co-incubated Enterococcus faecalis with a 99% population. Here we used an azo dye-decolorizing Enterococcus faecalis strain T6a1 and non-dye-decolorizing Bacillus subtilis strain S4ga. The dye decolorization assay enabled the investigation of the effects of Bacillus subtilis S4ga on the activity of Enterococcus faecalis T6a1, even when Bacillus subtilis S4ga was present at only 1% relative abundance or lower. We found that non-decolorizing Bacillus subtilis S4ga enhanced the dye decolorization activity of Enterococcus faecalis T6a1, shortened the lag time of Enterococcus faecalis T6a1 to start decreasing the dye concentration, and increased the time for Enterococcus faecalis T6a1 to continue dye decolorization. These effects were correlated with redox potential values. We compared the extracellular amino acids between each incubation culture of Enterococcus faecalis T6a1 and Bacillus subtilis S4ga, which revealed their mutual relationship by cross-feeding of specific amino acids. We also compared the intracellular primary metabolites between co-incubation and sole incubation of E. faecalis T6a1. The arginine deiminase (ADI) pathway in the co-incubated E. faecalis T6a1 was activated compared to that of E. faecalis T6a1 incubated solely. These findings explained that co-incubation with Bacillus subtilis S4ga promoted ATP production in Enterococcus faecalis T6a1 cells to a greater extent and enhanced dye-decolorization activity.