Characterization of newly isolated Pseudonocardia sp. N23 with high 1,4-dioxane-degrading ability

An investigation of soil and groundwater metagenomes for genes encoding soluble and particulate methane monooxygenase, toluene-4-monoxygenase, propane monooxygenase and phenol hydroxylase

Soil and groundwater were investigated for the genes encoding soluble and particulate methane monooxygenase/ammonia monooxygenase (sMMO, pMMO/AMO), toluene 4-monooxygenase (T4MO), propane monooxygenase (PMO) and phenol hydroxylase (PH). The objectives were (1) to determine which subunits were present, (2) to examine the diversity of the phylotypes associated with the biomarkers and (3) to identify which metagenome associated genomes (MAGs) contained these subunits. All T4MO and PH subunits were annotated in the groundwater metagenomes, while few were annotated in the soil metagenomes. The majority of the soil metagenomes included only four sMMO subunits. Only two groundwater metagenomes contained five sMMO subunits. Gene counts for the pMMO subunits varied between samples. The majority of the soil metagenomes were annotated for all four PMO subunits, while three out of eight groundwater metagenomes contained all four PMO subunits. A comparison of the blast alignments for the sMMO alpha chain (mmoX) indicated the phylotypes differed between the soil and groundwater metagenomes. For the pMMO/AMO alpha subunit (pmoA/amoA), Nitrosospira was important for the soil metagenomes, while Methylosinus and Methylocystis were dominant for the groundwater metagenomes. The majority of pmoA alignments from both metagenomes were from uncultured bacteria. High quality MAGs were obtained from the groundwater data. Four MAGs (Methylocella and Cypionkella) contained sMMO subunits. Another three MAGs, within the order Pseudomonadales, contained all three pMMO subunits. All PH subunits were detected in seven MAGs (Azonexus, Rhodoferax, Aquabacterium). In those seven, all contained catechol 2,3-dioxagenase, and Aquabacterium also contained catechol 1,2-dioxygenase. T4MO subunits were detected in eight MAGs (Azonexus, Rhodoferax, Siculibacillus) and all, except one, contained all six subunits. Four MAGs (Rhodoferax and Azonexus) contained all subunits for PH and T4MO, as well as catechol 2,3-dixoygenase. The detection of T4MO and PH in groundwater metagenomes and MAGs has important implications for the potential oxidation of groundwater contaminants.

Simultaneous biodegradation kinetics of 1,4-dioxane and ethane

Biodegradation of 1,4-Dioxane at environmentally relevant concentrations usually requires the addition of a primary electron-donor substrate to sustain biomass growth. Ethane is a promising substrate, since it is available as a degradation product of 1,4-Dioxane's common co-contaminants. This study reports kinetic parameters for ethane biodegradation and co-oxidations of ethane and 1,4-Dioxane. Based on experiments combined with mathematical modeling, we found that ethane promoted 1,4-Dioxane biodegradation when the initial mass ratio of ethane:1,4-Dioxane was < 9:1 mg COD/mg COD, while it inhibited 1,4-Dioxane degradation when the ratio was > 9:1. A model-independent estimator was used for kinetic-parameter estimation, and all parameter values for 1,4-Dioxane were consistent with literature-reported ranges. Estimated parameters support competitive inhibition between ethane as the primary substrate and 1,4-Dioxane as the secondary substrate. The results also support that bacteria that co-oxidize ethane and 1,4-Dioxane had a competitive advantage over bacteria that can use only one of the two substrates. The minimum concentration of ethane to sustain ethane-oxidizing bacteria and ethane and 1,4-Dioxane-co-oxidizing bacteria was 0.09 mg COD/L, which is approximately 20-fold lower than the minimum concentration reported for propane, another common substrate used to promote 1,4-Dioxane biodegradation. The minimum 1,4-Dioxane concentration required to sustain steady-state biomass with 1,4-Dioxane as the sole primary substrate was 1.3 mg COD/L. As 1,4-Dioxane concentrations at most groundwater sites are less than 0.18 mg COD/L, providing ethane as a primary substrate is vital to support biomass growth and consequently enable 1,4-Dioxane bioremediation.

Fabrication of Curcumin-Based Electrochemical Nanosensors for the Detection of Environmental Pollutants: 1,4-Dioxane and Hydrazine

This work reports the development of novel curcuminoid-based electrochemical sensors for the detection of environmental pollutants from water. In this study, the first set of electrochemical experiments was carried out using curcumin-conjugated multi-walled carbon nanotubes (MWCNT-CM) for 1,4-dioxane detection. The MWCNT-CM/GCE showed good sensitivity (103.25 nA nM-1 cm-2 in the linear range 1 nM to 1 µM), with LOD of 35.71 pM and LOQ of 108.21 pM. The second set of electrochemical experiments was carried out with bisdemethoxy curcumin analog quantum dots (BDMCAQD) for hydrazine detection. The BDMCAQD/GCE exhibited good sensitivity (74.96 nA nM-1 cm-2 in the linear range 100 nM to 1 µM), with LOD of 10 nM and LOQ of 44.93 nM. Thus, this work will serve as a reference for the fabrication of metal-free electrochemical sensors using curcuminoids as the redox mediator for the enhanced detection of environmental pollutants.

Degradation of 1,4-dioxane by heterogeneous photocatalysis and a photo-Fenton-like process under fluorescent light

The overall objective of this study was to develop cost-effective treatment processes for 1,4-dioxane removal that were safe and easy to scale up. Degradation of 1,4-dioxane was conducted and compared for the first time by heterogeneous photocatalysis and a photo-Fenton-like process under cool white fluorescent light in mild conditions, using two types of commercial nanoparticles-titanium dioxide (TiO2) and nanoscale zero-valent iron (nZVI), respectively. Both types of nanoparticles removed >99.9% of 1,4-dioxane in a short period of time. Hydroxyl radicals (·OH), superoxide radicals (·O2-), and hydrogen peroxide (H2O2) were detected in both degradation processes; photogenerated holes (h+) were critical in the degradation of 1,4-dioxane by the photocatalytic process using TiO2. 1,4-Dioxane can be degraded at pH 7 in TiO2/light system and at pH 3 in nZVI/light system, and faster degradation of 1,4-dioxane at even higher concentration was achieved in the former system. Increase in light intensity accelerated 1,4-dioxane degradation, which followed first order kinetics in both systems. In wastewater effluent, the removal of 1,4-dioxane was slower than that in deionised water, which likely reflected the complex compositions of the wastewater effluent. Under combined UVA and visible light illumination, a two-stage degradation process was proposed for 1,4-dioxane for the first time by TiO2 nanoparticles; this study also demonstrated for the first time 1,4-dioxane degradation by the photo-Fenton-like process using nZVI. The cost-effective solutions using commercial nanoparticles under fluorescent light developed in this study can be potentially applied to treat water contaminated by high concentrations of 1,4-dioxane in large-scale.

Isolation and characterization of pure cultures for metabolizing 1,4-dioxane in oligotrophic environments

1,4-Dioxane concentration in most contaminated water is much less than 1 mg/L, which cannot sustain the growth of most reported 1,4-dioxane-metabolizing pure cultures. These pure cultures were isolated following enrichment of mixed cultures at high concentrations (20 to 1,000 mg/L). This study is based on a different strategy: 1,4-dioxane-metabolizing mixed cultures were enriched by periodically spiking 1,4-dioxane at low concentrations (≤1 mg/L). Five 1,4-dioxane-metabolizing pure strains LCD6B, LCD6D, WC10G, WCD6H, and WD4H were isolated and characterized. The partial 16S rRNA gene sequencing showed that the five bacterial strains were related to Dokdonella sp. (98.3%), Acinetobacter sp. (99.0%), Afipia sp. (99.2%), Nitrobacter sp. (97.9%), and Pseudonocardia sp. (99.4%), respectively. Nitrobacter sp. WCD6H is the first reported 1,4-dioxane-metabolizing bacterium in the genus of Nitrobacter. The net specific growth rates of these five cultures are consistently higher than those reported in the literature at 1,4-dioxane concentrations <0.5 mg/L. Compared to the literature, our newly discovered strains have lower half-maximum-rate concentrations (1.8 to 8.2 mg-dioxane/L), lower maximum specific 1,4-dioxane utilization rates (0.24 to 0.47 mg-dioxane/(mg-protein ⋅ d)), higher biomass yields (0.29 to 0.38 mg-protein/mg-dioxane), and lower decay coefficients (0.01 to 0.02 d-1). These are characteristics of microorganisms living in oligotrophic environments.

Selective enrichment, identification, and isolation of diclofenac, ibuprofen, and carbamazepine degrading bacteria from a groundwater biofilm

Diclofenac, ibuprofen, and carbamazepine are three of the most widely detected and most concerning pharmaceutical residues in aquatic ecosystems. The aim of this study was to identify bacteria that may be involved in their degradation from a bacterial biofilm. Selective enrichment cultures in mineral salt solution containing pharmaceutical compounds as sole source of carbon and energy were set up, and population dynamics were monitored using shotgun metagenome sequencing. Bacterial genomes were reconstructed using genome-resolved metagenomics. Thirty bacterial isolates were obtained, identified at species level, and tested regarding pharmaceutical biodegradation at an initial concentration of 1.5 mg l-1. The results indicated that most probably diclofenac biodegrading cultures consisted of members of genera Ferrovibrio, Hydrocarboniphaga, Zavarzinia, and Sphingopyxis, while in ibuprofen biodegradation Nocardioides and Starkeya, and in carbamazepine biodegradation Nocardioides, Pseudonocardia, and Sphingopyxis might be involved. During the enrichments, compared to the initial state the percentage relative abundance of these genera increased up to three orders of magnitude. Except Starkeya, the genomes of these bacteria were reconstructed and annotated. Metabolic analyses of the annotated genomes indicated that these bacteria harbored genes associated with pharmaceutical biodegradation. Stenotrophomonas humi DIC_5 and Rhizobium daejeonense IBU_18 isolates eliminated diclofenac and ibuprofen during the tests in the presence of either glucose (3 g l-1) or in R2A broth. Higher than 90% concentration reduction was observed in the case of both compounds.

Pilot-scale biofiltration of 1,4-dioxane at drinking water-relevant concentrations

1,4-Dioxane is a drinking water contaminant of emerging concern. Because conventional and many advanced drinking water treatment technologies are ineffective for 1,4-dioxane removal, cost-effective technologies for the removal of 1,4-dioxane at drinking water-relevant concentrations are needed. In this research, a gravity-fed, cometabolic biofiltration system was developed to degrade 1,4-dioxane that was spiked into coagulated, settled surface water at a concentration of ∼10 µg/L. Objectives were to determine whether cometabolic degradation of trace levels of 1,4-dioxane can be sustained using n-butane as primary substrate and whether filter media properties and empty bed contact time (EBCT) affect biofiltration efficiency. A mixed culture of bacteria derived from the Cape Fear River basin and previously enriched using isobutane served as inoculum for biologically active filters. Two granular activated carbons (GACs) with different grain sizes and one carbonaceous resin were used as attachment media, and n-butane served as the primary substrate for biologically active filters. Non-inoculated controls with the same media were evaluated in parallel to distinguish between biological and adsorptive removals of 1,4-dioxane. For the duration of the pilot study (>3 months), 1,4-dioxane was degraded in inoculated biofilters receiving n-butane. In control filters containing larger and smaller grain GAC, 1,4-dioxane broke through completely within 750 and 1250 bed volumes, respectively, corresponding to 15 to 30 days of operation at an EBCT of 30 min. 1,4-Dioxane removal increased with increasing EBCT in all biologically active filters. At an EBCT of 30 min, the biologically active GAC filter containing the larger-grain GAC removed on average 87% of 1,4-dioxane at pseudo steady-state. When the hydraulic loading rate was decreased to achieve an overall EBCT of 60 min, 1,4-dioxane was removed to <1 µg/L in the biologically active GAC filter containing the larger-grain GAC. Activity-based labeling showed the presence of catalytically active monooxygenases in backwash water from biologically active filters that degraded 1,4-dioxane. Amplicon sequencing results showed that while taxa shifted after the initial inoculation of biologically active filters, taxa in biologically active filters remained more similar to the inoculum than those in the non-inoculated control filters. Overall, results of this research demonstrate that cometabolic degradation of 1,4-dioxane at trace levels is possible for extended periods of time in inoculated biofilters that receive n-butane as primary substrate.

A Review of Challenges and Opportunities for Microbially Removing 1,4-Dioxane to Meet Drinking-Water and Groundwater Guidelines

1,4-Dioxane is an emerging contaminant in drinking-water sources and contaminated sites. Microbial removal of 1,4-dioxane has attracted a lot of attention, but faces a challenge: being not able to continuously metabolize 1,4-dioxane to below most drinking-water and groundwater guidelines. The 1,4-dioxane concentrations in most drinking-water sources and contaminated sites are too low to sustain biomass growth. This minireview discusses strategies that may potentially address the challenge. The strategies include: 1) finding oligotrophs for which the minimum 1,4-dioxane concentrations to sustain biomass are low, 2) determining conditions that maximize 1,4-dioxane co-metabolism or co-oxidation, 3) creating novel materials as biomass carriers and contaminant concentrators, and 4) lowering the life-cycle costs of technologies that combine biodegradation with (electro)chemical oxidation or phytoremediation.

Efficient biodegradation of 1,4-dioxane commingled with additional organic compound: Role of interspecies interactions within consortia

Microbial consortia-mediated biodegradation of 1,4-dioxane (1,4-D), an emerging water contaminant, is always a superior choice over axenic cultures. Thus, better understanding of the functions of coexisting microbes and their interspecies interactions within the consortia is crucial for predicting biodegradation efficiency and designing efficient 1,4-D-degrading microbial consortia. This study evaluated how microbial community compositions and interspecies interactions govern the microbial consortia-mediated 1,4-D biodegradation by investigating the biodegradability and microbial community dynamics of both enriched (N112) and synthetic (SCDs and SCDNs) microbial consortia in the absence or presence of additional organic compound (AOC). In the absence of AOC, N112 exhibited 100% 1,4-D biodegradation efficiency at a rate of 12.5 mg/L/d, whereas the co-occurrence of AOC resulted in substrate-dependent biodegradation inhibition and thereby reduced the biodegradation efficiency and activity (2.0-10.0 mg/L/d). The coexistence and negative influence of certain low-abundant non-degraders on both 1,4-D-degraders and key non-degraders in N112 was identified as the prime cause behind such biodegradation inhibition. Comparing with N112, SCDN-1 composed of 1,4-D-degraders and key non-degraders significantly improved the 1,4-D biodegradation efficiency in the presence of AOC, confirming the absence of negative influence of low-abundant non-degraders and cooperative interactions between 1,4-D-degraders and key non-degraders in SCDN-1. On the contrary, both two-species and three-species SCDs comprised of only 1,4-D-degraders resulted in lower 1,4-D biodegradation efficiency as compared to SCDN-1 under all treatment conditions, while max. 91% 1,4-D biodegradation occurred by SCDs in the absence of AOC. These results were attributed to the negative interaction among 1,4-D-degraders and the absence of complementary roles of key non-degraders in SCDs. The findings improve our understanding of how interspecies interactions can regulate the intrinsic abilities and functions of coexisting microbes during biodegradation in complex environments and provide valuable guidelines for designing highly efficient and robust microbial consortia for practical bioremediation of 1,4-D like emerging organic contaminants.

Remedial strategies for abating 1,4-dioxane pollution-special emphasis on diverse biotechnological interventions

1,4-dioxane is a heterocyclic ether used as a polar industrial solvent and are released as waste discharges. 1,4-dioxane deteriorates health and quality, thereby attracts concern by the environment technologists. The need of attaining sustainable development goals have resulted in search of an eco-friendly and technically viable treatment strategy. This extensive review is aimed to emphasis on the (a) characteristics of 1,4-dioxane and their occurrence in the environment as well as their toxicity, (b) remedial strategies, such as physico-chemical treatment and advanced oxidation techniques. Special reference to bioremediation that involves diverse microbial strains and their mechanism are highlighted in this review. The role of macronutrients, stimulants and other abiotic cofactors in the biodegradation of 1,4-dioxane is discussed lucidly. We have critically discussed the inducible enzymes, enzyme-based remediation, distinct instrumental method of analyses to know the fate of intermediates produced from 1,4-dioxane biotransformation. This comprehensive survey also tries to put forth the different toxicity assessment tools used in evaluating the extent of detoxification of 1,4-dioxane achieved through biotransforming mechanism. Conclusively, the challenges, opportunities, techno-economic feasibility and future prospects of implementing 1,4-dioxane through biotechnological interventions are also discussed.

Effectiveness of tetrahydrofuran at enhancing the 1,4-dioxane degradation ability of activated sludge lacking prior exposure to 1,4-dioxane

1,4-dioxane (DX) is a contaminant of emerging concern in water environments. The enrichment of DX-degrading bacteria indigenous to activated sludge is key for the efficient biological removal of DX in wastewater. To identify an effective substrate, which enables the selective enrichment of DX-degrading bacteria and has lower toxicity and persistence than DX, this study explored the effectiveness of tetrahydrofuran (THF) at enhancing the DX degradation ability of activated sludge without historical exposure to DX. Although the activated sludge initially exhibited negligible ability to degrade DX (100 mg-C/L) as the sole carbon source, the repeated batch cultivation on THF could enrich bacterial populations capable of degrading DX, inducing the DX degradation ability in activated sludge as effectively as DX did. The THF-enrichment culture after 4 weeks degraded 100 mg-C/L DX almost completely within 21 d. Sequencing analyses revealed that soluble di-iron monooxygenase group 5C, including THF/DX monooxygenase, would play a dominant role in the initial oxidation of DX in THF-enrichment culture, which completely differed from the enrichment culture cultivated on DX. The results indicate that THF can be applied as an effective substrate to enhance the DX degradation ability of microbial consortia, irrespective of the intrinsic ability.

Response surface algorithm for improved biotransformation of 1,4-dioxane using Staphylococcus capitis strain AG

The present investigation reports the biotransformation of an endrocrine disrupting agent; 1,4-dioxane through bacterial metabolism. Initially, potential bacterial isolates capable of surviving with minimum 1,4-dioxane were screened from industrial wastewater. Thereafter, screening was done to isolate a bacteria which can biotransform higher concentration (1000 mg/L) of 1,4-dioxane. Morphological and biochemical features were examined prior establishing their phylogenetic relationships and the bacterium was identified as Staphylococcus capitis strain AG. Biotransformation experiments were tailored using response surface tool and predictions were made to elucidate the opimal conditions. Critical factors influencing bio-transformation efficiency such as tetrahydrofuran, availability of 1,4-dioxane and inoculum size were varied at three different levels as per the central composite design for ameliorating 1,4-dioxane removal. Functional attenuation of 1,4-dioxane by S. capitis strain AG were understood using spectroscopic techniques were significant changes in the peak positions and chemical shifts were visualized. Mass spectral profile revealed that 1.5 (% v/v) S. capitis strain AG could completely (∼99%) remove 1000 mg/L 1,4-dioxane, when incubated with 2 μg/L tetrahydrofuran for 96 h. The toxicity of 1,4-dioxane and biotransformed products by S. capitis strain AG were tested on Artemia salina. The results of toxicity tests revealed that the metabolic products were less toxic as they exerted minimal mortality rate after 48 h exposure. Thus, this research would be the first to report the response prediction and precise tailoring of 1,4-dioxane biotransformation using S. captis strain AG.

Enabling Efficient Genetic Manipulations in a Rare Actinomycete Pseudonocardia alni Shahu

Pseudonocardia species are emerging as important microorganisms of global concern with unique and increasingly significant ecological roles and represent a prominent source of bioactive natural products, but genetic engineering of these organisms for biotechnological applications is greatly hindered due to the limitation of efficient genetic manipulation tools. In this regard, we report here the establishment of an efficient genetic manipulation system for a newly isolated strain, Pseudonocardia alni Shahu, based on plasmid conjugal transfer from Escherichia coli to Pseudonocardia. Conjugants were yielded upon determining the optimal ratio between the donor and recipient cells, and designed genome modifications were efficiently accomplished, including exogenous gene integration based on an integrative plasmid and chromosomal stretch removal by homologous recombination using a suicidal non-replicating vector. Collectively, this work has made the P. alni Shahu accessible for genetic engineering, and provided an important reference for developing genetic manipulation methods in other rare actinomycetes.

Genus Pseudonocardia: What we know about its biological properties, abilities and current application in biotechnology

The genus Pseudonocardia belongs to a group of Actinomycetes, and is a member of the family Pseudonocardiacea. The members of this genus are aerobic, Gram-positive, non-motile bacteria that are commonly found in soil, plant and environment. Although this genus has a low clinical significance; however, it has an important role in biotechnology due to the production of secondary metabolites, some of which have anti-bacterial, anti-fungal and anti-tumour effects. The use of phenotypic tests, such as gelatinase activity, starch hydrolysis, catalase and oxidase tests, as well as molecular methods, such as polymerase chain reaction, are necessary for Pseudonocardia identification at the genus and species levels.

Treatment of 1,4-dioxane-containing water using carriers immobilized with indigenous microorganisms in landfill leachate treatment sludge: A laboratory-scale reactor study

1,4-Dioxane (DX) is a contaminant of emerging concern in aquatic environments, and is frequently found in landfill leachate. As a biological method applicable to landfill leachate treatment facilities, the feasibility of DX treatment using carriers immobilized with microorganisms indigenous to landfill leachate treatment sludge was explored through laboratory-scale reactor experiments by introducing carriers prepared via microorganism immobilization in the aeration tank of a leachate treatment facility. Three different carrier materials were used to immobilize microorganisms, and a model DX-containing water (10 mg/L) was treated under continuous feeding. Biological DX removal to < 0.5 mg/L was achieved using all carrier types, thereby adhering to the effluent standard for landfill leachate in Japan, which confirms the usefulness of the proposed method. However, weaker aeration and enhanced DX loading drastically impaired the DX removal performance depending on the carrier materials. This suggests the importance of carrier selection and control of the operational variables to ensure stable and effective DX removal. Microbial community analyses revealed that Pseudonocardia with thm genes may largely contribute to the initial oxidation of DX, irrespective of the carrier type, suggesting the importance of this population for the continuous treatment of low DX concentrations with mixed microbial consortia.

Chemo-metrically formulated consortium with selectively screened bacterial strains for ameliorated biotransformation and detoxification of 1,4-dioxane

The biotransformation of 1,4-dioxane, a endrocrine disrupting chemical was achieved using different bacterial strains and their consortia. Three different bacterial isolates were screened on their ability to grow with 50 mg/L 1,4-dioxane in the basal mineral medium. Then the isolates were tested for its efficiency to biotransform 1000 mg/L 1,4-dioxane at varying period of time; 24-120 h. The isolates were distinguished by their morphological features and 16 S rRNA gene sequencing was done to evaluate the phylogenetic relationships. The isolates were identified as Bacillus marisflavi strain MGA, Aeromonas hydrophila strain AG and Shewanella putrefaciens strain AG. The degree of biotransformation was escalated by constructing a bacterial consortium using statistical tool; response-mixture matrix under the design of experiments. The fully grown bacterial strains were used as ingredients in different proportions to formulate the consortium. The biotransformation was analyzed for functional attenuation using spectroscopic techniques and reduction in 1,4-dioxane level was confirmed using mass spectrometry. The precise quantification of biotransformation using mass spectral profile revealed that the consortium removed 31%, 61% and 85% of 1000 mg/L 1,4-dioxane within 96, 120 and 144 h respectively. The activities of inducible laccase were elucidated during biotransformation of 1,4-dioxane. Bio-toxicity of treated and untreated 1,4-dioxane on brine shrimp; Artemia salina showed that the biotransformed products were less toxic. Therefore, this report would be first of its kind to report the biotransformation and detoxification of 1,4-dioxane by a statistically designed bacterial consortium.

Cometabolic degradation of 1,4-dioxane by a tetrahydrofuran-growing Arthrobacter sp. WN18

1,4-Dioxane (dioxane), an emerging groundwater contaminant, is frequently detected in landfill leachates with its structural analog, tetrahydrofuran (THF). Along with undesirable leakage of landfill leachates, dioxane and THF inevitably percolate into groundwater leading to a broader region of contamination. Cometabolic bioremediation is an effective approach to manage commingled THF and dioxane pollution. In this study, a newly isolated bacterium Arthrobacter sp. WN18 is able to co-oxidize dioxane with THF as the primary substrate. Meanwhile, the THF-induced thmADBC gene cluster was responsible for the dioxane degradation rate indicating THF monooxygenase is the essential enzyme that initializing α-hydroxylation of THF and dioxane. Further, γ-butyrolactone and HEAA were characterized as the key metabolites of THF and dioxane, respectively. In addition, WN18 can tolerate the inhibition of trichloroethylene (5.0 mg/L) as a representative of co-existing leachate constituent, and sustain its activity at various pH (5-11), temperatures (15-42 °C), and salinities (up to 4%, as NaCl wt). Like other Arthrobacter species, WN18 also exhibited the capability of fixing nitrogen. All this evidence indicates the feasibility and advantage of WN18 as a thmADBC-catalyzed inoculator to bioremediate co-contamination of THF and dioxane.

Isolation and Characterization of Novel Bacteria Capable of Degrading 1,4-Dioxane in the Presence of Diverse Co-Occurring Compounds

Biodegradation is found to be a promising, cost-effective and eco-friendly option for the treatment of industrial wastewater contaminated by 1,4-dioxane (1,4-D), a highly stable synthetic chemical and probable human carcinogen. This study aimed to isolate, identify, and characterize metabolic 1,4-D-degrading bacteria from a stable 1,4-D-degrading microbial consortium. Three bacterial strains (designated as strains TS28, TS32, and TS43) capable of degrading 1,4-D as a sole carbon and energy source were isolated and identified as Gram-positive Pseudonocardia sp. (TS28) and Gram-negative Dokdonella sp. (TS32) and Afipia sp. (TS43). This study, for the first time, confirmed that the genus Dokdonella is involved in the biodegradation of 1,4-D. The results reveal that all of the isolated strains possess inducible 1,4-D-degrading enzymes and also confirm the presence of a gene encoding tetrahydrofuran/dioxane monooxygenase (thmA/dxmA) belonging to group 5 soluble di-iron monooxygenases (SDIMOs) in both genomic and plasmid DNA of each of the strains, which is possibly responsible for the initial oxidation of 1,4-D. Moreover, the isolated strains showed a broad substrate range and are capable of degrading 1,4-D in the presence of additional substrates, including easy-to-degrade compounds, 1,4-D biodegradation intermediates, structural analogs, and co-contaminants of 1,4-D. This indicates the potential of the isolated strains, especially strain TS32, in removing 1,4-D from contaminated industrial wastewater containing additional organic load. Additionally, the results will help to improve our understanding of how multiple 1,4-D-degraders stably co-exist and interact in the consortium, relying on a single carbon source (1,4-D) in order to develop an efficient biological 1,4-D treatment system.

Degradation of 1,4-Dioxane by Xanthobacter sp. YN2

1,4-Dioxane is a highly toxic and carcinogenic pollutant found worldwide in groundwater and soil environments. Several microorganisms have been isolated by their ability to grow on 1,4-dioxane; however, low 1,4-dioxane tolerance and slow degradation kinetics remain obstacles for their use in 1,4-dioxane bioremediation. We report here the isolation and characterization of a new strain, Xanthobacter sp. YN2, capable of highly efficient 1,4-dioxane degradation. High degradation efficiency and high tolerance to 1,4-dioxane make this new strain an ideal candidate for the biodegradation of 1,4-dioxane in various treatment facilities. The maximum degradation rate of 1,4-dioxane was found to be 1.10 mg-1,4-dioxane/h mg-protein. Furthermore, Xanthobacter sp. YN2 was shown to grow in the presence of higher than 3000 mg/L 1,4-dioxane with little to no degradation inhibition. In addition, Xanthobacter sp. YN2 could grow on and degrade 1,4-dioxane at pH ranges 5 to 8 and temperatures between 20 and 40 °C. Xanthobacter sp. YN2 was also found to be able to grow on a variety of other substrates including several analogs of 1,4-dioxane. Genome sequence analyses revealed the presence of two soluble di-iron monooxygenase (SDIMO) gene clusters, and regulation studies determined that all of the genes in these two clusters were upregulated in the presence of 1,4-dioxane. This study provides insights into the bacterial stress response and the highly efficient biodegradation of 1,4-dioxane as well as the identification of a novel Group-2 SDIMO.

Photocatalytic degradation of 1,4-dioxane using liquid phase plasma on visible light photocatalysts

The compound 1,4-dioxane (DO) irritates the eyes, skin, and mucous membrane and is classified as a carcinogen. In this study, the decomposition of DO by photocatalytic reaction using liquid phase plasma (LPP) with photocatalyst was suggested. Plasma was directly discharged as an aqueous DO solution to enhance photocatalytic decomposition activity. To increase the decomposition efficiency of DO by plasma, bismuth ferrite (BFO) prepared by a sol-gel method was introduced as a visible-light photocatalyst. In the application of LPP and BFO photocatalyst, the decomposition of DO by photocatalytic reaction was evaluated. BFO showed UV-vis diffusion reflectance spectroscopy results of absorption of UV and visible light over 600 nm, with a bandgap of approximately 2.2 eV. BFO showed visible light photochemical reaction characteristics to decompose particulate matter (PM) in the irradiation of 6 W visible light LED lamps. It seems that the narrow bandgap of BFO led to the photocatalytic activity in the visible light. In the decomposition reaction of DO with a photocatalyst and LPP, BFO showed better decomposition efficiency than TiO₂. BFO can cause photocatalytic reactions in both UV and visible light in the case of LPP irradiation, which emits strong ultraviolet and visible light.

Kinetic characterization of purified laccase from Trametes hirsuta: a study on laccase catalyzed biotransformation of 1,4-dioxane

OBJECTIVE

Laccase is one of the best known biocatalysts which degrade wide varieties of complex molecules that are both non-cyclic and cyclic in structure. The study focused on enzyme kinetics of a purified laccase from Trametes hirsuta L. fungus and its application on biotransformation of a carcinogenic molecule 1,4-dioxane.

RESULTS

Laccase was purified from white-rot fungus T. hirsuta L. which showed specific activity of 978.34 U/mg after the purification fold of 54.08. The stable laccase activity (up to 16 h) is shown at 4-6 pH and 20-40 °C temperature range. The purified enzyme exhibited significant stability for 10 metal ions up to 10 mM concentration, except for Fe²⁺ and Hg²⁺. The Cu²⁺ ion induced laccase activity up to 142% higher than the control at 10 mM concentration. The laccase enzyme kinetic parameters K_m was 20 ± 5 µM and 400 ± 60 µM, whereas K_cat was 198.29 ± 0.18/s and 80.20 ± 1.59/s for 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) and guaiacol respectively. The cyclic ether 1,4-dioxane (100 ppm) was completely degraded in presence of purified laccase within 2 h of incubation and it was confirmed by HPLC and GC analysis. The oxidation reaction was accelerated by 25, 22, 6 and 19% in presence of 1 mM syringaldehyde, vanillin, ABTS and guaiacol mediators respectively.

CONCLUSIONS

In this study, fungal laccase (a natural biocatalyst) based degradation of synthetic chemical 1,4-dioxane was reported for the first time. This method has added advantages over the multiple methods reported earlier being a natural remedy.

Investigating promising substrates for promoting 1,4-dioxane biodegradation: effects of ethane and tetrahydrofuran on microbial consortia

Cometabolic biodegradation of 1,4-dioxane (dioxane) in the presence of primary substrates is a promising strategy for treating dioxane at environmentally relevant concentrations. Seven aqueous amendments (i.e., tetrahydrofuran (THF), butanone, acetone, 1-butanol, 2-butanol, phenol and acetate) and five gaseous amendments (i.e., C₁-C₄ alkanes and ethylene) were evaluated as the primary substrates for dioxane degradation by mixed microbial consortia. The aqueous amendments were tested in microcosm bottles and the gaseous amendments were tested in a continuous-flow membrane biofilm reactor with hollow fibers pressurized by the gaseous amendments. Ethane was found to be the most effective gaseous substrate and THF was the only aqueous substrate that promoted dioxane degradation. A diverse microbial community consisting of several putative dioxane degraders-Mycobacterium, Flavobacterium and Bradyrhizobiaceae-were enriched in the presence of ethane. This is the first study showing that ethane was the most effective substrate among the short-chain alkanes and it promoted dioxane degradation by enriching dioxane-degraders that did not harbor the well-known dioxane/tetrahydrofuran monooxygenase.

Distinct Catalytic Behaviors between Two 1,4-Dioxane-Degrading Monooxygenases: Kinetics, Inhibition, and Substrate Range

Monitored natural attenuation (MNA) and engineered bioremediation have been recognized as effective and cost-efficient in situ treatments to mitigate 1,4-dioxane (dioxane) contamination. Dioxane metabolism can be initiated by two catabolic enzymes, propane monooxygenase (PRM) and tetrahydrofuran monooxygenase (THM), belonging to the group-6 and 5 of soluble di-iron monooxygenase family, respectively. In this study, we comprehensively compared catalytic behaviors of PRM and THM when individually expressed in the heterologous host, Mycobacterium smegmatis mc²-155. Kinetic results revealed a half-saturation coefficient (K_m) of 53.0 ± 13.1 mg/L for PRM, nearly 4 times lower than that of THM (235.8 ± 61.6 mg/L), suggesting that PRM has a higher affinity to dioxane. Exposure with three common co-contaminants (1,1-dichloroethene, trichloroethene, and 1,1,1-trichloroethane) demonstrated that PRM was also more resistant to their inhibition than THM. Thus, dioxane degraders expressing PRM may be more physiologically and ecologically advantageous than those with THM at impacted sites, where dioxane concentration is relatively low (e.g., 250 to 1000 μg/L) with co-occurrence of chlorinated solvents (e.g., 0.5 to 8 mg/L), underscoring the need of surveying both PRM and THM-encoding genes for MNA potential assessment. PRM is also highly versatile, which breaks down cyclic molecules (dioxane, tetrahydrofuran, and cyclohexane), as well as chlorinated and aromatic pollutants, including vinyl chloride, 1,2-dichloroethane, benzene, and toluene. This is the first report regarding the ability of PRM to degrade a variety of short-chain alkanes and ethene in addition to dioxane, unraveling its pivotal role in aerobic biostimulation that utilizes propane, isobutane, or other gaseous alkanes/alkenes (e.g., ethane, butane, and ethene) to select and fuel indigenous microorganisms to tackle the commingled contamination of dioxane and chlorinated compounds.

Stimulatory and inhibitory effects of metals on 1,4-dioxane degradation by four different 1,4-dioxane-degrading bacteria

This study evaluates the effects of various metals on 1,4-dioxane degradation by the following four bacteria: Pseudonocardia sp. D17; Pseudonocardia sp. N23; Mycobacterium sp. D6; and Rhodococcus aetherivorans JCM 14343. Eight transition metals [Co(II), Cu(II), Fe(II), Fe(III), Mn(II), Mo(VI), Ni(II), and Zn(II)] were used as the test metals. Results revealed, for the first time, that metals had not only inhibitory but also stimulatory effects on 1,4-dioxane biodegradation. Cu(II) had the most severe inhibitory effects on 1,4-dioxane degradation by all of the test strains, with significant inhibition at concentrations as low as 0.01-0.1 mg/L. This inhibition was probably caused by cellular toxicity at higher concentrations, and by inhibition of degradative enzymes at lower concentrations. In contrast, Fe(III) enhanced 1,4-dioxane degradation by Mycobacterium sp. D6 and R. aetherivorans JCM 14343 the most, while degradation by the two Pseudonocardia strains was stimulated most notably in the presence of Mn(II), even at concentrations as low as 0.001 mg/L. Enhanced degradation is likely caused by the stimulation of soluble di-iron monooxygenases (SDIMOs) involved in the initial oxidation of 1,4-dioxane. Differences in the stimulatory effects of the tested metals were likely associated with the particular SDIMO types in the test strains.

Enrichment and Analysis of Stable 1,4-dioxane-Degrading Microbial Consortia Consisting of Novel Dioxane-Degraders

Biodegradation of 1,4-dioxane, a water contaminant of emerging concern, has drawn substantial attention over the last two decades. A number of dioxane-degraders have been identified, though many of them are unable to metabolically utilize 1,4-dioxane. Moreover, it is considered more preferable to use microbial consortia rather than the pure strains, especially in conventional bioreactors for industrial wastewater treatment. In the present study, a stable 1,4-dioxane-degrading microbial consortium was enriched, namely 112, from industrial wastewater by nitrate mineral salt medium (NMSM). The consortium 112 is capable of utilizing 1,4-dioxane as a sole carbon and energy source, and can completely degrade 1,4-dioxane up to 100 mg/L. From the consortium 112, two 1,4-dioxane-degrading bacterial strains were isolated and identified, in which the Variovorax sp. TS13 was found to be a novel 1,4-dioxane-degrader that can utilize 100 mg/L of 1,4-dioxane. The efficacy of the consortium 112 was increased significantly when we cultured the consortium with mineral salt medium (MSM). The new consortium, N112, could utilize 1,4-dioxane at a rate of 1.67 mg/L·h. The results of the ribosomal RNA intergenic spacer analysis (RISA) depicted that changes in the microbial community structure of consortium 112 was the reason behind the improved degradation efficiency of consortium N112, which was exhibited as a stable and effective microbial consortium with a high potential for bioremediation of the dioxane-impacted sites and contaminated industrial wastewater.

Potential application of mixed metal oxide nanoparticle-embedded glassy carbon electrode as a selective 1,4-dioxane chemical sensor probe by an electrochemical approach

Here, low-dimensional mixed metal oxide (ZnO/NiO/MnO2) nanoparticles (NPs) were prepared to develop a selective, efficient and ultra-sensitive 1,4-dioxane sensor by using the wet-chemical method (co-precipitation) in alkaline medium at low temperature. Detailed characterization of the prepared calcined NPs was achieved via conventional methods, including X-ray diffraction, field emission scanning electron microscopy, and X-ray photoelectron, UV-vis, Fourier-transform infrared and energy dispersive X-ray spectroscopies. To develop a thin layer of nanomaterial on the fabricated electrode, a slurry of prepared NPs was used to coat the glassy carbon electrode (GCE) with conductive Nafion (5% in ethanol) binder. The fabricated electrochemical sensor showed good sensitivity (1.0417 μA μM-1 cm-2), a wide linear dynamic range (0.12 nM to 1.2 mM), lower detection limit (9.14 ± 4.55 pM), short response time, good reproducibility, and long-term stability to selectively detect 1,4-dioxane in the optimized buffer system. Thus, this work presents a reliable alternative approach over existing methods to selectively detect hazardous chemicals in large scale for safety in the environmental and healthcare fields.

Carbon sources that enable enrichment of 1,4-dioxane-degrading bacteria in landfill leachate

1,4-Dioxane (DX) is a recalcitrant cyclic ether that has gained attention as an emerging pollutant in the aquatic environment. Enrichment of indigenous DX-degrading bacteria, which are considered to be minor populations even in DX-impacted environments, is the key for efficient biological DX removal. Therefore, this study aimed to explore carbon sources applicable for the enrichment of DX-degrading bacteria present in landfill leachate, which is a potential source of DX pollution. Microorganisms collected from landfill leachate were cultivated on six different carbon sources (DX, tetrahydrofuran (THF), 1,3,5-trioxane (TX), ethylene glycol (EG), diethylene glycol (DEG), and 1,4-butanediol (BD)) in a sequential batch mode. Consequently, enrichment cultures cultivated on THF in addition to DX improved the DX degradation ability compared to that of the original leachate sample, while those on the other test carbon sources did not. The results indicated that THF can be an alternative carbon source to enrich DX-degrading bacteria, and that TX, EG, DEG and BD are not applicable to concentrate DX-degrading bacteria in complex microbial consortia. In addition, sequencing analyses of 16S rRNA and soluble di-iron monooxygenase (SDIMO) genes revealed notable dominance of thm/dxm genes involved in group 5 SDIMO both in DX- and THF-enrichment cultures. The analysis also showed a predominance of Pseudonocardia in THF-enrichment culture, suggesting that Pseudonocardia harboring thm/dxm genes contributes to enhanced DX degradation in THF-enrichment culture.

Exploring the glyphosate-degrading characteristics of a newly isolated, highly adapted indigenous bacterial strain, Providencia rettgeri GDB 1

This study explored the characteristics of a newly isolated glyphosate (GLYP)-degrading bacterium Providencia rettgeri GDB 1, for GLYP bioremediation. Due to the serial selection pressure of high GLYP concentrations for enriched isolation, this highly tolerant GLYP biodegrader shows very promising capabilities for GLYP removal (approximately 71.4% degradation efficiency) compared to previously reported strains. High performance liquid chromatography analyses showed aminomethylphosphonic acid (AMPA) rather than sarcosine (SAR) to be the sole intermediate of GLYP decomposition via the AMPA formation pathway. Moreover, GLYP biodegradation was biochemically favorable in aerobic cultures due to its strong growth-associated characteristics. To the best of our knowledge, this is the first report to indicate that bacterial strains in the Providencia genus could demonstrate highly promising GLYP-degrading characteristics in environments with high GLYP contents.

Microbial Community Analysis Provides Insights into the Effects of Tetrahydrofuran on 1,4-Dioxane Biodegradation

Tetrahydrofuran (THF) is known to induce the biodegradation of 1,4-dioxane (dioxane), an emerging contaminant, but the mechanisms by which THF affects dioxane biodegradation in microbial communities are not well understood. To fill this knowledge gap, changes in the microbial community structure in microcosm experiments with synthetic medium and landfill leachate were examined over time using 16S rRNA gene amplicon sequencing and functional gene quantitative PCR assays. The overarching hypothesis being tested was that THF promoted dioxane biodegradation by increasing the abundance of dioxane-degrading bacteria in the consortium. The data revealed that in experiments with synthetic medium, the addition of THF significantly increased the abundance of Pseudonocardia, a genus with several representatives that can grow on both dioxane and THF, and of Rhodococ cus ruber, a species that can use THF as the primary growth substrate while cometabolizing dioxane. However, in similar experiments with landfill leachate, only R. ruber was significantly enriched. When the THF concentration was higher than the dioxane concentration, THF competitively inhibited dioxane degradation since dioxane degradation was negligible, while the dioxane-degrading bacteria and the corresponding THF/dioxane monooxygenase gene copies increased by a few orders of magnitude.IMPORTANCE Widespread in groundwater and carcinogenic to humans, 1,4-dioxane (dioxane) is attracting significant attention in recent years. Advanced oxidation processes can effectively remove dioxane but require high energy consumption and operation costs. Biological removal of dioxane is of particular interest due to the ability of some bacteria to mineralize dioxane at a low energy cost. Although dioxane is generally considered recalcitrant to biodegradation, more than 20 types of bacteria can degrade dioxane as the sole electron donor substrate or the secondary electron donor substrate. In the latter case, tetrahydrofuran (THF) is commonly studied as the primary electron donor substrate. Previous work has shown that THF promotes dioxane degradation at a low THF concentration but inhibits dioxane degradation at a high THF concentration. Our work expanded on the previous work by mechanically examining the effects of THF on dioxane degradation in a microbial community context.

1,4-Dioxane degradation characteristics of Rhodococcus aetherivorans JCM 14343

Rhodococcus aetherivorans JCM 14343 can degrade 1,4-dioxane as a sole carbon and energy source. This study aimed to characterize this 1,4-dioxane degradation ability further, and assess the potential use of the strain for 1,4-dioxane removal in industrial wastewater. Strain JCM 14343 was able to degrade 1,4-dioxane inducibly, and its 1,4-dioxane degradation was also induced by tetrahydrofuran and 1,4-butanediol. The demonstration that 1,4-butanediol not only induced but also enhanced 1,4-dioxane degradation was a novel finding of this study. Although strain JCM 14343 appeared not to be an effective 1,4-dioxane degrader considering the maximum specific 1,4-dioxane degradation rate (0.0073 mg-dioxane/mg-protein/h), half saturation concentration (59.2 mg/L), and cell yield (0.031 mg-protein/mg-1,4-dioxane), the strain could degrade over 1100 mg/L of 1,4-dioxane and maintain its degradation activity at a wide range of temperature (5-40 °C) and pH (4-9) conditions. This suggests the usefulness of strain JCM 14343 in 1,4-dioxane treatment under acidic and cold conditions. In addition, 1,4-dioxane degradation experiments in the presence of ethylene glycol (EG) or other cyclic ethers revealed that 1,4-dioxane degradation by strain JCM 14343 was inhibited in the presence of other cyclic ethers, but not by EG, suggesting certain applicability of strain JCM 14343 for industrial wastewater treatment.