Decolorization and biodegradation of triphenylmethane dyes by a novel Rhodococcus qingshengii JB301 isolated from sawdust

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.

Inhibit or promote? Trade-off effect of dissolved organic matter on the laccase-mediator system

A biocatalytic system comprising fungal laccase and mediators can generate phenol radicals and efficiently eliminate various triarylmethane dyes. This study systematically explores the kinetic impact of dissolved organic matter (DOM), represented by humic substance (HS consisting of 90% fulvic acid, from lignite), on the decolorization of seven typical triarylmethane dyes by Trametes versicolor laccase and twenty natural mediators. Among these, 4-hydroxybenzyl alcohol (4-HA) and methyl violet (MV) undergo in-depth investigation regarding degradation products, pathways, and reaction mechanisms. In instances where HS hampers laccase-alone decolorization, such as malachite green, Coomassie brilliant blue, bromophenol blue, and acid magenta, this inhibition may persist despite mediator introduction. Conversely, in cases where HS facilitates decolorization, such as crystalline violet and ethyl violet, most laccase-mediator systems (LMSs) can still benefit. For MV decolorization by laccase and 4-HA, HS's kinetic effect is controlled by concentration and reaction time. A 5 mg/L HS increased the decolorization rate from 50% to 67% within the first hour, whereas 10 mg/L HS only achieved 45%. After 16 h of reaction, HS's impact on decolorization rate diminishes. Furthermore, the addition of HS enhances precipitation production, probably due to its involvement in polymerization with MV and mediator. Computational simulations and spectral monitoring reveal that low HS concentrations accelerate laccase-mediated demethylation by disrupting the chromophores bound to MV, thus promoting the decolorization of MV. Conversely, inhibition by high HS concentrations stems from the competitive binding of the enzyme pocket to the mediator, and the reduction of phenol free radicals in the system. Molecular docking and kinetic simulations revealed that laccase forms complexes with both the mediator and MV. Interestingly, the decolorization of MV occurred through a non-radical mechanism in the presence of HS. This work provided a reference for screening of high catalytic performance mediators to remove triarylmethane dyes in the actual water environment.

Complete Genome Sequence of Rhodococcus qingshengii Strain PM1, Isolated from a Selenium-Rich Mine in China

Rhodococcus qingshengii PM1 was isolated from selenium-rich carbonaceous mudstones in Enshi, Hubei, China. Here, we report the complete genome sequence of this strain, which was obtained by combining Illumina and Nanopore sequencing.

Rhodococcus: A promising genus of actinomycetes for the bioremediation of organic and inorganic contaminants

Rhodococcus is a genus of actinomycetes that has been explored by the scientific community for different purposes, especially for bioremediation uses. However, the mechanisms governing Rhodococcus-mediated bioremediation processes are far from being fully elucidated. In this sense, this work aimed to compile the recent advances in the use of Rhodococcus for the bioremediation of organic and inorganic contaminants present in different environmental compartments. We reviewed the bioremediation capacity and mechanisms of Rhodococcus spp. in the treatment of polycyclic aromatic hydrocarbons, phenolic substances, emerging contaminants, heavy metals, and dyes given their human health risks and environmental concern. Different bioremediation techniques were discussed, including experimental conditions, treatment efficiencies, mechanisms, and degradation pathways. The use of Rhodococcus strains in the bioremediation of several compounds is a promising approach due to their features, primarily the presence of appropriate enzyme systems, which result in high decontamination efficiencies; but that vary according to experimental conditions. Besides, the genus Rhodococcus contains a small number of opportunistic species and pathogens, representing an advantage from the point of view of safety. Advances in analytical detection techniques and Molecular Biology have been collaborating to improve the understanding of the mechanisms and pathways involved in bioremediation processes. In the context of using Rhodococcus spp. as bioremediation agents, there is a need for more studies that 1) evaluate the role of these actinomycetes on a pilot and field scale; 2) use genetic engineering tools and consortia with other microorganisms to improve the bioremediation efficiency; and 3) isolate new Rhodococcus strains from environments with extreme and/or contaminated conditions aiming to explore their adaptive capabilities for bioremediation purposes.

Synthesis of nZnO from waste batteries by hydrometallurgical method for photocatalytic degradation of organic pollutants under visible light irradiation

Waste zinc carbon (Zn-C) batteries are generated worldwide in a large amount. They are non-rechargeable and costly to recycle. Therefore, they end up in the landfills where they create hazards for humans and for environment as well. Zn-C batteries are rich in concentration of different heavy metals so they can be subjected for the recovery of metals for the development of valuable new materials. In this study authors have proposed an easy hydrometallurgical method for the recovery of zinc from waste Zn-C batteries to synthesize nano zinc oxide (nZnO) photocatalyst. The prepared nZnO particles were irregular in shape, highly crystalline in nature with crystallite size 23.94 nm. The band gap of the photocatalyst was 3.1 eV. The photocatalytic activity of the synthesised nZnO was tested for the degradation of three organic pollutants namely; phenol, p-nitrophenol (PNP) and crystal violet dye (CV) in an aqueous solution under visible light irradiation. nZnO showed a good catalytic efficiency for the degradation of all the three pollutants, however, the crystal violet (CV) removal was best in comparison with the other pollutants, it was minimally effected by the increase in CV concentration. The maximum degradation of phenol, PNP and CV was found to be 95.03 ± 0.2%, 88.63 ± 0.1% and 97.87 ± 0.4%, respectively. The degradation data was fitted best with pseudo-first-order kinetic model. The photocatalyst was recyclable and its regeneration ability was higher for initial three cycles. The intermediate compounds formed in the process of degradation were determined by liquid chromatography and mass spectroscopy (LC-MS) analysis.

Heterologous expression of azoreductase-encoding gene azrS of Bacillus sp. MR-1/2 for enhanced azo dye decolorization and wastewater treatment

In Pakistan, 55% of textile exports are contributed by textile-units of Faisalabad. The effluents of these textile units, being discharged without any treatment, contain the contamination of a huge amount of synthetic azo dyes. The objective of the current research was to evaluate the contribution of an azoreductase-encoding gene (azrS) from a pre-characterized azo dye decolorizing bacterial strain Bacillus sp. MR-1/2 in a high copy number host system (pUC19-T7-Top-T) of Escherichia coli strain DH5α followed by in-silico prediction of azoreductase enzyme (AzrS) function. The recombinant cells that contained azrS had a significantly higher rate of color removal in congo red and reactive black-5 dyes when compared to wild-type MR-1/2 and E. coli DH5α after 72 h of incubation. Moreover, we were able to show that the recombinant strain significantly reduced the values of all tested parameters (pH, EC, turbidity, TSS, and COD) in actual wastewater. In support of our results, it was also predicted through bioinformatics analysis that the deduced azoreductase protein of strain MR-1/2 is linked with the dye decolorization ability of the strain through NAD(P)H-ubiquinone: oxidoreductase activity. Furthermore, we also found that the deduced protein resembled closely related proteins of protein databank in many features, yet some unique features were predicted in the enzyme activity of strain MR-1/2. It was concluded that the recombinant strain could be examined in pilot-scale experiments for textile wastewater treatment.

Draft genome sequence and nomenclature adjustment of Rhodococcus qingshengii CS98, a cesium-accumulating strain isolated in Japan

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Nomenclature of Rhodococcus erythropolis CS98 has been revised to Rhodococcus qingshengii 98.

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Genome analysis reveals large number of genes involved in DNA repair and stress responses.

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Organism a possible candidate for bioremediation of soil contaminated by radiocaesium.

Strains within the Rhodococcus genus have the ability to endure a range of recalcitrant compounds and metabolise a variety of pollutants. As a result there is increasing interest in these robust prokaryotes for their applications in bioremediation of contaminated environments and bioconversion of industrial wastes. In this announcement we present the draft genome sequence of R. qingshengii CS98, a soil isolate from Japan with the demonstrated ability to accumulate both stable and radioactive caesium.

Decolourization and biodegradation of azo dye methyl red by Rhodococcus strain UCC 0016

In the present study, locally isolated Rhodococcus strains were attempted as biological tools for methyl red removal, a mutagenic azo dye posing threat to the environment if left untreated. Rhodococcus strain UCC 0016 demonstrated superior methyl red-decolourizing activity of 100% after 24 h at static condition in comparison to Rhodococcus strain UCC 0008 which recorded 65% decolourization after 72 h. Optimization of physicochemical parameters at 30°C, pH 7 and supplementing glucose as the carbon source resulted in improved methyl red-decolourizing activity at static condition and reduced the time taken to achieve complete decolourization by 80%. Higher concentration of methyl red (5 g/L) was able to be decolourized completely within 10 h by adopting the technology of immobilization. The encapsulated cells of Rhodococcus strain UCC 0016 demonstrated higher substrate affinity (K_m = 0.6995 g/L) and an accelerated rate of disappearance of methyl red (V_max = 0.3203 g/L/h) compared to the free cells. Furthermore, the gellan gum beads could be reused up to nine batches without substantial loss in the catalytic activity indicating the economic importance of this protocol. Analysis of methyl red degradation products revealed no germination inhibition on Triticum aestivum and Vigna radiata demonstrating complete toxicity removal of the parent dye after biological treatment. The occurrence of new and altered peaks (UV-Vis and FTIR) further supported the notion that the removal of methyl red by Rhodococcus strain UCC 0016 was indeed through biodegradation. Therefore, this strain has a huge potential as a candidate for efficient bioremediation of wastewater containing methyl red.

Use of RSM modeling for optimizing decolorization of simulated textile wastewater by Pseudomonas aeruginosa strain ZM130 capable of simultaneous removal of reactive dyes and hexavalent chromium

Remediation of colored wastewater loaded with dyes and metal ions is a matter of interest nowadays. In this study, 220 bacteria isolated from textile wastewater were tested for their potential to decolorize each of the four reactive dyes (reactive red-120, reactive black-5, reactive yellow-2, and reactive orange-16) in the presence of a mixture of four different heavy metals (Cr, Zn, Pb, Cd) commonly found in textile effluents. Among the tested bacteria, the isolate ZM130 was found to be the most efficient in decolorizing reactive dyes in the presence of the mixture of heavy metals and was identified as Pseudomonas aeruginosa strain ZM130 by 16S rRNA gene analysis. The strain ZM130 was highly effective in simultaneously removing hexavalent chromium (25 mg L(-1)) and the azo dyes (100 mg L(-1)) from the simulated wastewater even in the presence of other three heavy metals (Zn, Pb, Cd). Simultaneous removal of chromium and azo dyes ranged as 76.6-98.7 % and 51.9-91.1 %, respectively, after 180 h incubation. On the basis of quadratic polynomial equation and response surfaces given by the response surface methodology (RSM), optimal salt content, pH, carbon co-substrate content, and level of multi-metal mixtures for decolorization of reactive red-120 in a simulated textile wastewater by the strain ZM130 were predicted to be 19.8, 7.8, and 6.33 g L(-1) and a multi-metal mixture (Cr 13.10 mg L(-1), Pb 26.21 mg L(-1), Cd 13.10 mg L(-1), Zn 26.21 mg L(-1)), respectively. Moreover, the strain ZM130 also exhibited laccase and nicotinamide adenine dinucleotide (reduced)-dichlorophenolindophenol reductase (NADH-DCIP reductase) activity during the decolorization of reactive red-120. However, the laccase activity was found to be maximum in the presence of 300 mg L(-1) of the dye as compared to other concentrations. Hence, the isolation of this strain might serve as a potential bio-resource required for developing the strategies aiming at bioremediation of the wastewater contaminated with dyes and heavy metals.