Efficient production of R-2-(4-hydroxyphenoxy) propionic acid by Beauveria bassiana using biofilm-based two-stage fermentation

In this work, a novel biofilm-based fermentation of Beauveria bassiana was employed to convert R-2- phenoxypropionic acid (R-PPA) to R-2-(4-hydroxyphenoxy) propionic acid (R-HPPA). The biofilm culture model of Beauveria bassiana produced a significantly higher R-HPPA titer than the traditional submerged fermentation method. Mannitol dosage, tryptone dosage, and initial pH were the factors that played a significant role in biofilm formation and R-HPPA synthesis. Under the optimal conditions, the maximum R-HPPA titer and productivity approached 22.2 g/L and 3.2 g/(L·d), respectively. A two-stage bioreactor combining agitation and static incubation was developed to further increase R-HPPA production. The process was optimized to achieve 100 % conversion of R-PPA, with a maximum R-HPPA titer of 50 g/L and productivity of 3.8 g/(L·d). This newly developed biofilm-based two-stage fermentation process provides a promising strategy for the industrial production of R-HPPA and related hydroxylated aromatic compounds.

Rice Husk-Cellulose-Based Agricultural Waste Enhances the Degradation of Synthetic Dyes Using Multiple Enzyme-Producing Extremophiles

The brightly colored synthetic dyes used in the textile industry are discharged at high concentrations-for example, various azo dyes including Methylene Blue (MB) and Methyl Orange (MO)-which is a matter of global concern, as such dyes are harmful to humans and the environment. Microbial degradation is considered an efficient alternative for overcoming the disadvantages of conventional physical and chemical dye removal methods. In this study, we investigated the potential of multiple types of the enzyme-producing extremophilic bacteria Bacillus FW2, isolated from food waste leachate, for the decolorization and bioremediation of artificial synthetic dyes. The screening of enzyme production and assaying of bacterial strain enzymes are essential for enhancing the breakdown of azo bonds in textile azo dyes. The degradation efficiencies of the water-soluble dyes MB and MO were determined at different concentrations using rice husk, which is an efficient substrate. Using the rice husks, the MO was removed completely within 20 h, and an estimated 99.8% of MB was degraded after 24 h by employing shaking at 120 rpm at 40 °C-whereas a removal efficiency of 98.9% was achieved for the combination of MB + MO. These results indicate the possibility of applying an extremophilic bacterial strain, Bacillus sp., for large-scale dye degradation in the future.

Investigating Bio-Inspired Degradation of Toxic Dyes Using Potential Multi-Enzyme Producing Extremophiles

Biological treatment methods overcome many of the drawbacks of physicochemical strategies and play a significant role in removing dye contamination for environmental sustainability. Numerous microorganisms have been investigated as promising dye-degrading candidates because of their high metabolic potential. However, few can be applied on a large scale because of the extremely harsh conditions in effluents polluted with multiple dyes, such as alkaline pH, high salinity/heavy metals/dye concentration, high temperature, and oxidative stress. Therefore, extremophilic microorganisms offer enormous opportunities for practical biodegradation processes as they are naturally adapted to multi-stress conditions due to the special structure of their cell wall, capsule, S-layer proteins, extracellular polymer substances (EPS), and siderophores structural and functional properties such as poly-enzymes produced. This review provides scientific information for a broader understanding of general dyes, their toxicity, and their harmful effects. The advantages and disadvantages of physicochemical methods are also highlighted and compared to those of microbial strategies. New techniques and methodologies used in recent studies are briefly summarized and discussed. In particular, this study addresses the key adaptation mechanisms, whole-cell, enzymatic degradation, and non-enzymatic pathways in aerobic, anaerobic, and combination conditions of extremophiles in dye degradation and decolorization. Furthermore, they have special metabolic pathways and protein frameworks that contribute significantly to the complete mineralization and decolorization of the dye when all functions are turned on. The high potential efficiency of microbial degradation by unculturable and multi-enzyme-producing extremophiles remains a question that needs to be answered in practical research.

Bioprospecting of novel ligninolytic bacteria for effective bioremediation of agricultural by-product and synthetic pollutant dyes

Lignin is a significant renewable carbon source that needs to be exploited to manufacture bio-ethanol and chemical feedstocks. Lignin mimicking methylene blue (MB) dye is widely used in industries and causes water pollution. Using kraft lignin, methylene blue, and guaiacol as a full carbon source, 27 lignin-degrading bacteria (LDB) were isolated from 12 distinct traditional organic manures for the current investigation. The ligninolytic potential of 27 lignin-degrading bacteria was assessed by qualitative and quantitative assay. In a qualitative plate assay, the LDB-25 strain produced the largest zone, measuring 6.32 ± 0.297, on MSM-L-kraft lignin plates, while the LDB-23 strain produced the largest zone, measuring 3.44 ± 0.413, on MSM-L-Guaiacol plates. The LDB-9 strain in MSM-L-kraft lignin broth was able to decolorize lignin to a maximum of 38.327 ± 0.011% in a quantitative lignin degradation assay, which was later verified by FTIR assay. In contrast, LDB-20 produced the highest decolorization (49.633 ± 0.017%) in the MSM-L-Methylene blue broth. The highest manganese peroxidase enzyme activity, measuring 6322.314 ± 0.034 U L^-1, was found in the LDB-25 strain, while the highest laccase enzyme activity, measuring 1.5105 ± 0.017 U L^-1, was found in the LDB-23 strain. A preliminary examination into the biodegradation of rice straw using effective LDB was carried out, and efficient lignin-degrading bacteria were identified using 16SrDNA sequencing. SEM investigations also supported lignin degradation. LDB-8 strain had the highest percentage of lignin degradation (52.86%), followed by LDB-25, LDB-20, and LDB-9. These lignin-degrading bacteria have the ability to significantly reduce lignin and lignin-analog environmental contaminants, therefore they can be further researched for effective bio-waste management mediated breakdown.

Bacillus subtilis: As an Efficient Bacterial Strain for the Reclamation of Water Loaded with Textile Azo Dye, Orange II

The azo dye orange II is used extensively in the textile sector for coloring fabrics. High concentrations of it are released into aqueous environments through textile effluents. Therefore, its removal from textile wastewater and effluents is necessary. Herein, initially, we tested 11 bacterial strains for their capabilities in the degradation of orange II dye. It was revealed in the preliminary data that B. subtilis can more potently degrade the selected dye, which was thus used in the subsequent experiments. To achieve maximum decolorization, the experimental conditions were optimized whereby maximum degradation was achieved at: a 25 ppm dye concentration, pH 7, a temperature of 35 °C, a 1000 mg/L concentration of glucose, a 1000 mg/L urea concentration, a 666.66 mg/L NaCl concentration, an incubation period of 3 days, and with hydroquinone as a redox mediator at a concentration of 66.66 mg/L. The effects of the interaction of the operational factors were further confirmed using response surface methodology, which revealed that at optimum conditions of pH 6.45, a dye concentration of 17.07 mg/L, and an incubation time of 9.96 h at 45.38 °C, the maximum degradation of orange II can be obtained at a desirability coefficient of 1, estimated using the central composite design (CCD). To understand the underlying principles of degradation of the metabolites in the aliquot mixture at the optimized condition, the study steps were extracted and analyzed using GC-MS(Gas Chromatography Mass Spectrometry), FTIR(Fourier Transform Infrared Spectroscopy), ¹H and carbon 13 NMR(Nuclear Magnetic Resonance Spectroscopy). The GC-MS pattern revealed that the original dye was degraded into o-xylene and naphthalene. Naphthalene was even obtained in a pure state through silica gel column isolation and confirmed using ¹H and ¹³C NMR spectroscopic analysis. Phytotoxicity tests on Vigna radiata were also conducted and the results confirmed that the dye metabolites were less toxic than the parent dye. These results emphasize that B. subtilis should be used as a potential strain for the bioremediation of textile effluents containing orange II and other toxic azo dyes.