Effective decolorization of anthraquinone dye reactive blue 19 using immobilized Bacillus sp. JF4 isolated by resuscitation-promoting factor strategy

Enhanced degradation of phthalate esters (PAEs) by biochar-sodium alginate immobilised Rhodococcus sp. KLW-1

In this study, a new strain of bacteria, named Rhodococcus sp. KLW-1, was isolated from farmland soil contaminated by plastic mulch for more than 30 years. To improve the application performance of free bacteria and find more ways to use waste biochar, KLW-1 was immobilised on waste biochar by sodium alginate embedding method to prepare immobilised pellet. Response Surface Method (RSM) predicted that under optimal conditions (3% sodium alginate, 2% biochar and 4% CaCl2), di (2-ethylhexyl) phthalate (DEHP) degradation efficiency of 90.48% can be achieved. Under the adverse environmental conditions of pH 5 and 9, immobilisation increased the degradation efficiency of 100 mg/L DEHP by 16.42% and 11.48% respectively, and under the high-stress condition of 500 mg/L DEHP concentration, immobilisation increased the degradation efficiency from 71.52% to 91.56%, making the immobilised pellets have strong stability and impact load resistance to environmental stress. In addition, immobilisation also enhanced the degradation efficiency of several phthalate esters (PAEs) widely existing in the environment. After four cycles of utilisation, the immobilised particles maintained stable degradation efficiency for different PAEs. Therefore, immobilised pellets have great application potential for the remediation of the actual environment.

Anaerobic biodegradation of azo dye reactive black 5 by a novel strain Shewanella sp. SR1: Pathway and mechanisms

The efficiency of microbial populations in degrading refractory pollutants and the impact of adverse environmental factors often presents challenges for the biological treatment of azo dyes. In this study, the genome analysis and azo dye Reactive Black 5 (RB5) degrading capability of a newly isolated strain, Shewanella sp. SR1, were investigated. By analyzing the genome, functional genes involved in dye degradation and mechanisms for adaptation to low-temperature and high-salinity conditions were identified in SR1. The addition of co-substrates, such as glucose and yeast extract, significantly enhanced RB5 decolorization efficiency, reaching up to 87.6%. Notably, SR1 demonstrated remarkable robustness towards a wide range of NaCl concentrations (1-30 g/L) and temperatures (10-30 °C), maintaining efficient decolorization and high biomass concentration. The metabolic pathways of RB5 degradation were deduced based on the metabolites and genes detected in the genome, in which the azo bond was first cleaved by FMN-dependent NADH-azoreductase and NAD(P)H-flavin reductase, followed by deamination, desulfonation, and hydroxylation mediated by various oxidoreductases. Importantly, the degradation metabolites exhibited reduced toxicity, as revealed by toxicity analysis. These findings highlighted the great potential of Shewanella sp. SR1 for bioremediation of wastewaters contaminated with azo dyes.

Simultaneous adsorption and biodegradation of polychlorinated biphenyls using resuscitated strain Streptococcus sp. SPC0 immobilized in polyvinyl alcohol‑sodium alginate

Enhanced bioremediation of polychlorinated biphenyls (PCBs) is a promising and effective strategy for eliminating the risks posed by PCBs. In the present study, the feasibility of utilizing an immobilization approach to enhance the PCBs degradation performance of a resuscitated strain Streptococcus sp. SPC0 was evaluated. The results indicated that a mixed matrix containing polyvinyl alcohol (PVA) and sodium alginate (SA) used as immobilized carriers provided a porous microstructure space for SPC0 colonization and proliferation. The enhanced removal of PCBs by immobilized SPC0 was attributed to simultaneous adsorption and biodegradation performances of PVA-SA-SPC0 beads. The relative equilibrium adsorption capacity of immobilized beads increased with elevated initial concentration, and the maximum theoretical value calculated was 1.64 mg/g. The adsorption process of PCBs by immobilized beads was well fitted to the quasi-second-order kinetic model, and most suitable for Langmuir isotherm model. Immobilized SPC0 enhanced PCB removal with 1.0-7.1 times higher than free cells. Especially, more effective removal of PCBs at higher concentrations could be achieved, in which 73.9 % of 20 mg/L PCBs was removed at 12 h by immobilized SPC0, whereas only 12.0 % by free cells. Moreover, the immobilized SPC0 with excellent stability and reusability retained almost 100 % of the original PCBs removal activity after reusing four times. These results revealed the application potential of immobilizing resuscitated strains for enhanced bioremediation of PCBs.

Co-metabolic biodegradation of structurally discrepant dyestuffs by Klebsiella sp. KL-1: A molecular mechanism with regards to the differential responsiveness

In this study, an attempt was made to decipher the underlying differential response mechanism of Klebsiella sp. KL-1 induced by exposure to disparate categories of dyestuffs in xylose (Xyl) co-metabolic system. Here, representative reactive black 5 (RB5), remazol brilliant blue R (RBBR) and malachite green (MG) belonging to the azo, anthraquinone and triphenylmethane categories were employed as three model dyestuffs. Klebsiella sp. KL-1 enabled nearly 98%, 80% or 97% removal of contaminants in assays Xyl + RB5, Xyl + RBBR or Xyl + MG after 48 h, which was respectively 16%, 11% or 22% higher than those in the assays devoid of xylose. LC-QTOF-MS revealed an increased formation of smaller molecular weight intermediates in assay Xyl + RB5, whereas more metabolic pathways were deduced in assay Xyl + RBBR. Metaproteomics analysis displayed remarkable proteome alteration with regards to the structural difference effect of dyestuffs by Klebsiella sp. KL-1. Significant (p-value<0.05) activation of pivotal candidate NADH-quinone oxidoreductase occurred after 48 h of disparate dyestuff exposure but with varying abundance. Dominant FMN-dependent NADH-azoreductase, Cytochrome d terminal oxidase or Thiol peroxidase were likewise deemed to be responsible for the catalytic cleavage of RB5, RBBR or MG, respectively. Further, the differential response mechanism towards the structurally discrepant dyestuffs was put forward. Elevated reducing force associated with the corresponding functional proteins/enzymes was transferred to the exterior of the cell to differentially decompose the target contaminants. Overall, this study was dedicated to provide in-depth insights into the molecular response mechanism of co-metabolic degradation of refractory and structurally discrepant dyestuffs by an indigenous isolated Klebsiella strain.

Use of bacterial isolates in the treatment of textile dye wastewater: A review

The textile industry uses large amounts of dyes like reactive, azo, anthraquinone, and triphenylmethane to colour textiles. Dyes that are not used up during the colouration process usually end up in water bodies as waste leading to the pollution of the water bodies. This makes the industry to be one of the major contributors to water pollution in the world. Bacterial agents isolated from various sources like dye contaminated soil and textile wastewater have shown to have the ability to effectively decolourise and degrade these dye pollutants leading to improved water quality. This review discusses bacterial isolates that have been used successfully to degrade and decolourise textile dyes, their mode of dye removal as well as the factors that affect their dye degradation ability. It further looks at the latest wastewater treatment technologies that incorporate bacterial microorganisms to treat dye wastewater.

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Bacterial isolates offer environmentally friendly solution to dye degradation.

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Pure and mixed bacterial cultures can remove textile dyes in optimised conditions.

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Dyes are removed through biosorption or biodegradation mechanisms.

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Latest technologies provide more effective dye removal options.

Bioremediation of soil contaminated with toxic mixed reactive azo dyes by co-cultured cells of Enterobacter cloacae and Bacillus subtilis

Azo dyes, known for its toxicity and mutagenicity, are used by textile industries. Bioremediation serves the best alternative treatment process due to its eco-friendly nature and cost-effectiveness. Degradation using individual bacteria promotes azo dye removal, while the degradation is enhanced using the immobilization method. Bio-carrier promotes the attachment of the bacterial strains and increases azo dye degradation. The present study focuses on the biodegradation of Reactive Red (RR), Reactive Brown (RB), Reactive Black dye (RBL), and mixed dyes in a soil slurry bioreactor containing free cells, co-culture, and immobilized cells. The physico-chemical analysis and soil characteristics were determined. The free cells of Bacillus cereus showed degradation of azo dyes - 79.42 ± 0.03% RR, 78.78 ± 0.02% RBL; 70.76 ± 0.03% RB, and 84.89 ± 0.05% of mixed dyes respectively. Enterobacter cloacae free cells resulted in degradation of 72.87 ± 0.01% RR, 75.21 ± 0.01% RBL, 74.50 ± 0.02% RB, and 73.39 ± 0.04% mixed dyes respectively. Co-cultured bacterial strains resulted in 77.18 ± 0.03% RR, 80.27 ± 0.02% RBL, 76.97 ± 0.02% RB and 86.29 ± 0.05% mixed dyes respectively. The immobilization of Bacillus cereus and Enterobacter cloacae on 2% corn starch resulted in 98.4 ± 0.01% degradation of RR, 89.8 ± 0.09% degradation of RB, 99.4 ± 0.05% of RBL, and 98.1 ± 0.08% of mixed reactive dyes respectively.

Unlocking the potential of biosynthesized zinc oxide nanoparticles for degradation of synthetic organic dyes as wastewater pollutants

The azo dyes released into water from different industries are accumulating in the water bodies and bioaccumulating within living systems thereby affecting environmental health. This is a major concern in developing countries where stringent regulations are not followed for the discharge of industrial waste into water bodies. This has led to the accumulation of various pollutants including dyes. As these developing countries also face acute water shortages and due to the lack of cost-effective systems to remove these pollutants, it is essential to remove these toxic dyes from water bodies, eradicate dyes, or generate fewer toxic derivatives. The photocatalysis mechanism of degradation of azo dyes has gained importance due to its eco-friendly and non-toxic roles in the environment. The zinc nanoparticles act as photocatalysts in combination with plant extracts. Plant-based nanoparticles over the years have shown the potential to degrade dyes efficiently. This is carried out by adjusting the dye and nanoparticle concentrations and combinations of nanoparticles. Our review article considers increasing the efficiency of degradation of dyes using zinc oxide (ZnO) nanoparticles and understanding the photocatalytic mechanisms in the degradation of dyes and the toxic effects of these dyes and nanoparticles in different tropic levels.

Exploitation of extracellular organic matter from Micrococcus luteus to enhance ex situ bioremediation of soils polluted with used lubricants

Chronic pollution by used lubricant oils (ULOs) poses a serious challenge to the environment. Under stress conditions, microorganisms, including potential degraders, can enter a viable but non-culturable (VBNC) state, complicating the bioremediation of ULO-polluted areas. Resuscitation-promoting factors (Rpfs) can reverse this transition and/or enhance the biodegradation performance of both native and augmented strains. Here, Rpf-containing extracellular organic matter (EOM) from Micrococcus luteus was used to enhance the ex situ ULO removal in biostimulated and bioaugmented (with Rhodococcus qingshengii KAG C, R. erythropolis PR4) soils. ULO bioconversion, microbial activity, and CFUs were significantly higher in EOM-treated soils compared to corresponding control soils. After 60 days, the initial ULO concentration (52,500 mg kg^-1) was reduced by 37% and 45% with EOM-supplemented biostimulation and bioaugmentation, respectively. Based on high-throughput 16S rRNA analysis, the enhancement was attributable both to the reactivation of EOM-responsive hydrocarbonoclastic bacterial genera (e.g., Pseudomonas, Comamonas, Stenotrophomonas, Gordonia) and to the long-term positive effect of EOM on the degradative efficacy of the introduced rhodococci. Ecotoxicological responses revealed that reduced ULO concentration did not correlate with decreased soil toxicity. Our findings provide an insight into the applicability of EOM in bioremediation and its effects on the soil microbial activity and community composition.

Microalgal-bacterial granular sludge process outperformed aerobic granular sludge process in municipal wastewater treatment with less carbon dioxide emissions

The aerobic granular sludge (AGS) process and microalgal-bacterial granular sludge (MBGS) process were comparably applied for municipal wastewater treatment in sequencing batch reactors with a height to diameter ratio of eight. For morphological appearances, the yellow aerobic granules were strip-shaped (4.0 mm × 0.62 mm) while the green microalgal-bacterial granules were elliptical-shaped (2.0 mm × 0.75 mm). The dominated rod-shaped bacteria (e.g., Acidobacteria and Bacteroidetes) and the slender configuration might be associated with the strip shape of aerobic granules under weak acid conditions. The nutrients removal performances by MBGS process were generally slightly better than AGS process. In addition, nutrients removal mechanisms were identified to elucidate how organics, ammonia, and phosphorus were removed by AGS process and MBGS process, respectively. Mass balance calculation estimated that MBGS process appeared to achieve much less CO₂ emission (5.8%) compared with AGS process (44.4%). Overall, it proved that MBGS process, with the merits of potentially low energy cost, limited CO₂ emission, and excellent performance, showed more prospects in municipal wastewater treatment than AGS process.

A novel strategy for enhancing anaerobic biodegradation of an anthraquinone dye reactive blue 19 with resuscitation-promoting factors

Anaerobic process has been widely applied as a cost-effective method for textile wastewater treatment. However, many bacteria exhibit low metabolic activity in unfavorable conditions due to the entry into a viable but non-culturable (VBNC) state. Thus, in this study, a novel method of using resuscitation-promoting factors (Rpfs), which has been proven to resuscitate and stimulate the growth of VBNC bacteria, is explored to enhance the degradation of the anthraquinone dye reactive blue 19 (RB19) in the anaerobic process. The results show that Rpfs could efficiently prompt RB19 decolorization. Compared to the conventional anaerobic condition, RB19 decolorization efficiency was increased by more than 20% with the Rpf addition. UV-visible spectral and gas chromatograph-mass spectrometry analysis indicate that the aromatic amines structures of RB19 was cleaved. More importantly, the Rpf addition appeared to stimulate and/or enrich some dye-degrading species of the family Peptostreptococcaceae, thus leading to a higher RB19 decolorization efficiency.

Enhancement of polychlorinated biphenyl biodegradation by resuscitation promoting factor (Rpf) and Rpf-responsive bacterial community

The activities of indigenous bacterial communities in polychlorinated biphenyls (PCBs) contaminated environments is closely related to the efficiency of bioremediation processes. Using resuscitation promoting factor (Rpf) from Micrococcus luteus is a promising method for resuscitation and stimulation of functional bacterial populations under stressful conditions. This study aims to use the Rpf to accelerate the biodegradation of Aroclor 1242, and explore putative PCB degraders which were resuscitated by Rpf addition. The Rpf-responsive bacterial populations were investigated using culture-dependent and culture-independent approaches, respectively. The results confirm that Rpf was capable of enhancing PCB degradation of enriched cultures from PCB-contaminated soils, and improving the activities of cultures with low tolerance to PCBs. High-throughput 16S rRNA analysis displays that the Rpf greatly altered the composition and abundance of bacterial populations in the phylum Proteobacteria. Identification of the resuscitated strains further suggests that the Rpf-responsive population was mostly represented by Sphingomonas and Pseudomonas, which are most likely the key PCB-degraders for enhanced biodegradation of PCBs.

Optimization of bacterial cytokine protein production by response surface methodology for environmental bioremediation

In natural and engineered systems, most microorganisms would enter a state of dormancy termed as “viable but non-culturable” (VBNC) state when they are exposed to unpredictable environmental stress. One of the major advances in resuscitating from such a state is the discovery of a kind of bacterial cytokine protein called resuscitation-promoting factor (Rpf), which is secreted from Micrococcus luteus. In this study, the optimization of Rpf production was investigated by the response surface methodology (RSM). Results showed that an empirical quadratic model well predicted the Rpf yield, and the highest Rpf protein yield could be obtained at the optimal conditions of 59.56 mg L⁻¹ IPTG, cell density 0.69, induction temperature 20.82 °C and culture time 7.72 h. Importantly, Phyre2 web portal characterized the structure of the Rpf domain to have a shared homology with lysozymes, and the highest lysozyme activity was at pH 5 and 50 °C. This study broadens the knowledge of Rpf production and provided potential strategies to apply Rpf as a bioactivator for environmental bioremediation.

A group of secreted proteins from M. luteus, recognized as resuscitation promoting factors (Rpf) can resuscitate the viable but non-culturable (VBNC) state bacteria which have the potential function of environmental bioremediation.

Genome-based analysis to understanding rapid resuscitation of cryopreserved anammox consortia via sequential supernatant addition

Simple cryopreservation of anaerobic ammonium-oxidation (anammox) consortia has become a promising preservation technology for the fast start-up of the anammox process. Here, we use genome-resolved metagenomics and metatranscriptomics to understand of the microbial interaction in a simple and effective resuscitation process for long-term cryopreserved anammox consortia by sequential addition of anammox SBR supernatant. Performance results showed that sequential addition of anammox supernatant significantly reduced the resuscitation time of the granule-based anammox process from 40 to 20 days. Genome-centric metagenomics were used to recover 19 high-quality draft genomes of anammox and heterotrophic bacteria. Comparative metatranscriptomic analysis was conducted to examine the gene expression of Candidatus Kuenenia stuttgartiensis, the dominant anammox bacterium, and heterotrophic bacteria to better understand their potential interactions. Proteobacteria-affiliated bacteria found in the supernatant were highly active in producing the secondary metabolites molybdopterin cofactor and folate which are needed for growth of the auxotrophic anammox bacteria. In addition, the significantly higher expression levels of hzsA and CO₂-fixtion genes in the Candidatus Kuenenia genome indicated the anammox bacteria were likely more active and growing faster after sequential anammox supernatant addition during the resuscitation process. The resuscitation treatment pulse assays confirmed that sequential addition of supernatant was an effective way for the rapid resuscitation of anammox consortia. Our findings offer the first evidence of cross-feeding during the rapid resuscitation of cryopreserved anammox consortia.

Quorum quenching altered microbial diversity and activity of anaerobic membrane bioreactor (AnMBR) and enhanced methane generation

A facultative bacterium Microbacterium sp. (QQ strain) was found significantly mitigated membrane biofouling and also increased methane production. It was found genera Nitrospira, norank-c-Bacterodetes vadinHA17, Trichococcus and family Anaerolineaceae were likely responsible for membrane biofouling. The presence of QQ strain increased the total abundance of fermentative and acetogenic genera by 0.61% and 379.61%, respectively, but had a minor effect on the abundance of methanogens. The increased methane production was likely due to the strengthened methanogenic activity and more available substrates. Homo-acetogenic Treponema was enriched (9.01%) in the presence of QQ strain suggesting that apart from hydrogenotrophic methanogenic pathway, extra CH₄ could be also produced from the additional acetate synthesized via homo-acetogenic pathway. This study advances knowledge about the effects of QQ strain on microbial communities, microbiota biofouling behavior and anaerobic fermentation process in AnMBRs.

In-situ membrane fouling control by electrooxidation and microbial community in membrane electro-bioreactor treating aquaculture seawater

Ammonia and nitrite in aquaculture recirculating seawater need to be strictly controlled to avoid deleterious effects on aquatic organisms. However, traditional biological approach can hardly meet the standard due to the short hydraulic retention time (HRT) and nitrite accumulation. A Membrane Electro-Bioreactor (MEBR) was developed for ammonia removal enhancement and in-situ electrochemical membrane fouling mitigation. The fouling mechanism was first found to proceed via the standard filtration model. The flux decrease was mainly caused by an internal pore clogging phenomenon. Membrane fouling resistance was enhanced by increasing anode potential from 0 to 1.4 V vs. SCE (Saturated Calomel Electrode). The ammonia removal rate in the MEBR was above 95% (HRT: 2 h, after day-13) and membrane fouling was mitigated that operation duration was extended by 71.4%. Higher total proportion of Proteobacteria, Bacteroidetes, Planctomycetes and Actinobacteria was obtained in the MEBR, suggesting higher nitrification and nitrogen removal potentials.

Bacterial eutrophic index for potential water quality evaluation of a freshwater ecosystem

Water quality evaluation of freshwater ecosystems has been widely reported based on the physical and chemical parameters of water (e.g., Carlson's trophic state index (TSI)), while the aquatic microorganisms are actually a more intuitive way to reflect the eutrophic levels. This article was based on 27 global freshwater ecosystems including freshwater rivers, lakes, and reservoirs. Bacterial eutrophic index (BEI) was determined as the function of temperature and abundances of Cyanobacteria and Actinobacteria. BEI and TSI values of the freshwater ecosystems were determined and the correlation analysis of TSI and BEI indicated their positive correlation (ρ = 0.452, p < 0.01). Furthermore, an eutrophication classification based on BEI was proposed. It turned out that BEI was a possible feasible method for water quality evaluation. The aquatic microorganism-based method such as BEI should be considered for water quality evaluation of a freshwater ecosystem. Complicated models combined with physicochemical (e.g., TSI) and microbial (e.g., BEI) method are recommended for water quality evaluation of a freshwater ecosystem in future.

Resuscitation, isolation and immobilization of bacterial species for efficient textile wastewater treatment: A critical review and update

Given highly complex and recalcitrant nature of synthetic dyes, textile wastewater poses a serious challenge on surrounding environments. Until now, biological treatment of textile wastewater using efficient bacterial species is still considered as an environmentally friendly and cost-effective approach. The advances in resuscitating viable but non-culturable (VBNC) bacteria via signaling compounds such as resuscitation-promoting factors (Rpfs) and quorum sensing (QS) autoinducers, provide a vast majority of potent microbial resources for biological wastewater treatment. So far, textile wastewater treatment from resuscitating and isolating VBNC state bacteria has not been critically reviewed. Thus, this review aims to provide a comprehensive picture of resuscitation, isolation and application of bacterial species with this new strategy, while the recent advances in synthetic dye decolorization were also elaborated together with the mechanisms involved. Discussion was further extended to immobilization methods to tackle its application. We concluded that the resuscitation of VBNC bacteria via signaling compounds, together with biochar-based immobilization technologies, may lead to an appealing biological treatment of textile wastewater. However, further development and optimization of the integrated process are still required for their wide applications.

Using pH as a single indicator for evaluating/controlling nitritation systems under influence of major operational parameters

This study focused on using pH as a single indicator to evaluate/control the performance of the nitritation system under the influence of three major operational parameters, and a total of fifteen batch tests were conducted. Results indicated that there were important interactions among different operational parameters and pH in the nitritation system; it was possible to propose the optimal nitritation operation scheme to compensate for negative changes in operational parameters. The optimal carbon to nitrogen (C/N) ratio was kept at 2.0 to ensure efficient removal of ammonium. The reaction time was the lowest (150 min) with the temperature = 20 °C, C/N = 0, and sludge/water ratio = 1:1. However, the C/N ratio could be adjusted to close to zero by reducing the temperature to about 10 °C, weakening the heterotrophic bacteria, and supplying sufficient biomass. The C/N ratio and sludge/water ratio could also be set at 4.0 and 1:3 respectively to deal with the impact of low temperature and organic matter. Results of this study might be useful to explain the optimal conditions and process control schemes with pH as a single indicator.