Response and recovery of microbial communities subjected to oxidative and biological treatments of 1,4-dioxane and co-contaminants

Widespread distribution of the DyP-carrying bacteria involved in the aflatoxin B1 biotransformation in Proteobacteria and Actinobacteria

Aflatoxin is one of the most notorious mycotoxins, of which aflatoxin B1 (AFB1) is the most harmful and prevalent. Microbes play a crucial role in the environment for the biotransformation of AFB1. In this study, a bacterial consortium, HS-1, capable of degrading and detoxifying AFB1 was obtained. Here, we combined multi-omics and cultivation-based techniques to elucidate AFB1 biotransformation by consortium HS-1. Co-occurrence network analysis revealed that the key taxa responsible for AFB1 biotransformation in consortium HS-1 mainly belonged to the phyla Proteobacteria and Actinobacteria. Moreover, metagenomic analysis showed that diverse microorganisms, mainly belonging to the phyla Proteobacteria and Actinobacteria, carry key functional enzymes involved in the initial step of AFB1 biotransformation. Metatranscriptomic analysis indicated that Paracoccus-related bacteria were the most active in consortium HS-1. A novel bacterium, Paracoccus sp. strain XF-30, isolated from consortium HS-1, contains a novel dye-decolorization peroxidase (DyP) enzyme capable of effectively degrading AFB1. Taxonomic profiling by bioinformatics revealed that DyP, which is involved in the initial biotransformation of AFB1, is widely distributed in metagenomes from various environments, primarily taxonomically affiliated with Proteobacteria and Actinobacteria. The in-depth examination of AFB1 biotransformation in consortium HS-1 will help us to explore these crucial bioresources more sensibly and efficiently.

Influence of temperature on performance and mechanism of advanced synergistic nitrogen removal in lab-scale denitrifying filter with biogenic manganese oxides

Temperature is a significant operational parameter of denitrifying filter (DF), which affects the microbial activity and the pollutants removal efficiency. This study investigated the influence of temperature on performance of advanced synergistic nitrogen removal (ASNR) of partial-denitrification anammox (PDA) and denitrification, consuming the hydrolytic and oxidation products of refractory organics in the actual secondary effluent (SE) as carbon source. When the test water temperature (TWT) was around 25, 20, 15 and 10 °C, the filtered effluent total nitrogen (TN) was 1.47, 1.70, 2.79 and 5.52 mg/L with the removal rate of 93.38%, 92.25%, 87.33% and 74.87%, and the effluent CODcr was 8.12, 8.45, 10.86 and 12.29 mg/L with the removal rate of 72.41%, 66.17%, 57.35% and 51.87%, respectively. The contribution rate of PDA to TN removal was 60.44%∼66.48%, and 0.77-0.96 mg chemical oxygen demand (CODcr) was actually consumed to remove 1 mg TN. The identified functional bacteria, such as anammox bacteria, manganese oxidizing bacteria (MnOB), hydrolytic bacteria and denitrifying bacteria, demonstrated that TN was removed by the ASNR, and the variation of the functional bacteria along the DF layer revealed the mechanism of the TWT affecting the efficiency of the ASNR. This technique presented a strong adaptability to the variation of the TWT, therefore, it has broad application prospect and superlative application value in advanced nitrogen removal of municipal wastewater.

Metagenomic insights into the diversity of 2,4-dichlorophenol degraders and the cooperation patterns in a bacterial consortium

2,4-Dichlorophenol, which is largely employed in herbicides and industrial production, is frequently detected in ecosystems and poses risks to human health and environmental safety. Microbial communities are thought to perform better than individual strains in the complete degradation of organic contaminants. However, the synergistic degradation mechanisms of the microbial consortia involved in 2,4-dichlorophenol degradation are still not widely understood. In this study, a bacterial consortium named DCP-2 that is capable of degrading 2,4-dichlorophenol was obtained. Metagenomic analysis, cultivation-dependent functional verification, and co-occurrence network analysis were combined to reveal the primary 2,4-dichlorophenol degraders and the cooperation patterns in the consortium DCP-2. Metagenomic analysis showed that Pseudomonas, Achromobacter, and Pigmentiphaga were the primary degraders for the complete degradation of 2,4-dichlorophenol. Thirty-nine phylogenetically diverse bacterial genera, such as Brucella, Acinetobacter, Aeromonas, Allochromatium and Bosea, were identified as keystone taxa for 2,4-dichlorophenol degradation by keystone taxa analysis of the co-occurrence networks. In addition, a stable synthetic consortium of isolates from DCP-2 was constructed, consisting of Pseudomonas sp. DD-13 and Brucella sp. FZ-1; this synthetic consortium showed superior degradation capability for 2,4-dichlorophenol in both mineral salt medium and wastewater compared with monoculture. The findings provide valuable insights into the practical bioremediation of 2,4-dichlorophenol-contaminated sites.

Self-assembling a 1,4-dioxane-degrading consortium and identifying the key role of Shinella sp. through dilution-to-extinction and reculturing

IMPORTANCE

Assembling a functional microbial consortium and identifying key degraders involved in the degradation of 1,4-dioxane are crucial for the design of synergistic consortia used in enhancing the bioremediation of 1,4-dioxane-contaminated sites. However, due to the vast diversity of microbes, assembling a functional consortium and identifying novel degraders through a simple method remain a challenge. In this study, we reassembled 1,4-dioxane-degrading microbial consortia using a simple and easy-to-operate method by combining dilution-to-extinction and reculture techniques. We combined differential analysis of community structure and metabolic function and confirmed that Shinella species have a stronger 1,4-dioxane degradation ability than Xanthobacter species in the enriched consortium. In addition, a new dioxane-degrading bacterium was isolated, Shinella yambaruensis, which verified our findings. These results demonstrate that DTE and reculture techniques can be used beyond diversity reduction to assemble functional microbial communities, particularly to identify key degraders in contaminant-degrading consortia.

Underpinning the ecological response of mixed chlorinated volatile organic compounds (CVOCs) associated with contaminated and bioremediated groundwaters: A potential nexus of microbial community structure and function for strategizing efficient bioremediation

Understanding the structure, dynamics, and functionality of microbial communities is essential for developing sustainable and effective bioremediation strategies, particularly for sites contaminated with mixed chlorinated volatile organic compounds (CVOCs), which can make the biodegradation process more complex and challenging. In this study, 16S rRNA amplicon sequencing revealed a significant change in microbial distribution in response to CVOCs contamination. The loss of sensitive taxa such as Proteobacteria and Acidobacteriota was observed, while CVOCs-resistant taxa such as Campilobacterota were found significantly enriched in contaminated sites. Additionally, varying abundances of crucial enzymes involved in the sequential biodegradation of CVOCs were expressed depending on the contamination level. Association analysis revealed that specific genera such as Sulfurospirillum, Azospira, Trichlorobacter, Acidiphilium, and Magnetospririllum could relatively survive under higher levels of CVOC contamination, whereas pH, ORP and temperature had a negative influence in their abundance and distribution. However, Dechloromonas, Thiobacillus, Pseudarcicella, Hydrogenophaga, and Sulfuritalea showed a negative relationship with CVOC contamination, highlighting their sensitivity towards CVOC contamination. These findings provide valuable insights into the relationship among ecological responses, the groundwater bacterial community, and their functionality in response to mixed CVOC contamination, offering a fundamental basis for developing effective and sustainable bioremediation strategies for CVOC-contaminated groundwater systems.

Promoted wet peroxide oxidation of chlorinated volatile organic compounds catalyzed by FeOCl supported on macro-microporous biomass-derived activated carbon

Chlorinated volatile organic compounds (CVOCs) are a recalcitrant class of air pollutants, and the strongly oxidizing reactive oxygen species (ROS) generated in advanced oxidation processes (AOPs) are promising to degrade them. In this study, a FeOCl-loaded biomass-derived activated carbon (BAC) has been used as an adsorbent for accumulating CVOCs and catalyst for activating H₂O₂ to construct a wet scrubber for the removal of airborne CVOCs. In addition to well-developed micropores, the BAC has macropores mimicking those of biostructures, which allows CVOCs to diffuse easily to its adsorption sites and catalytic sites. Probe experiments have revealed HO^• to be the dominant ROS in the FeOCl/BAC + H₂O₂ system. The wet scrubber performs well at pH 3 and H₂O₂ concentrations as low as a few mM. It is capable of removing over 90% of dichloroethane, trichloroethylene, dichloromethane and chlorobenzene from air. By applying pulsed dosing or continuous dosing to replenish H₂O₂ to maintain its appropriate concentration, the system achieves good long-term efficiency. A dichloroethane degradation pathway is proposed based on the analysis of intermediates. This work may provide inspiration for the design of catalyst exploiting the inherent structure of biomass for catalytic wet oxidation of CVOCs or other contaminants.

Biodegradation of 1,4-dioxane by a native digestate microbial community under different electron accepting conditions

The potential of a native digestate microbial community for 1,4-dioxane (DX) biodegradation was evaluated under low dissolved oxygen (DO) concentrations (1-3 mg/L) under different conditions in terms of electron acceptors, co-substrates, co-contaminants and temperature. Complete DX biodegradation (detection limit of 0.01 mg/L) of initial 25 mg/L was achieved in 119 days under low DO concentrations, while complete biodegradation happened faster at 91 and 77 days, respectively in nitrate-amended and aerated conditions. In addition, conducting biodegradation at 30 ˚C showed that the time required for complete DX biodegradation in unamended flasks reduced from 119 days in ambient condition (20-25 °C) to 84 days. Oxalic acid, which is a common metabolite of DX biodegradation was identified in the flasks under different treatments including unamended, nitrate-amended and aerated conditions. Furthermore, transition of the microbial community was monitored during the DX biodegradation period. While the overall richness and diversity of the microbial community decreased, several families of known DX-degrading bacteria such as Pseudonocardiaceae, Xanthobacteraceae and Chitinophagaceae were able to maintain and grow in different electron-accepting conditions. The results suggested that DX biodegradation under low DO concentrations, where no external aeration was provided, is possible by the digestate microbial community, which can be helpful to the ongoing research for DX bioremediation and natural attenuation.

A review of whole-process control of industrial volatile organic compounds in China

Volatile organic compounds (VOCs) play an important role in the formation of ground-level ozone and secondary organic aerosol (SOA), and they have been key issues in current air pollution prevention and control in China. Considerable attention has been paid to industrial activities due to their large and relatively complex VOCs emissions. The present research aims to provide a comprehensive review on whole-process control of industrial VOCs, which mainly includes source reduction, collection enhancement and end-pipe treatments. Lower VOCs materials including water-borne ones are the keys to source substitution in industries related to coating and solvent usage, leak detection and repair (LDAR) should be regarded as an efficient means of source reduction in refining, petrochemical and other chemical industries. Several types of VOCs collection methods such as gas-collecting hoods, airtight partitions and others are discussed, and airtight collection at negative pressure yields the best collection efficiency. Current end-pipe treatments like UV oxidation, low-temperature plasma, activated carbon adsorption, combustion, biodegradation, and adsorption-combustion are discussed in detail. Finally, several recommendations are made for future advanced treatment and policy development in industrial VOCs emission control.

Tea-Soybean Intercropping Improves Tea Quality and Nutrition Uptake by Inducing Changes of Rhizosphere Bacterial Communities

The positive aspects of the tea plant/legume intercropping system draw attention to the Chinese tea industry for its benefit for soil fertility improvement with low fertilizer input. However, limited information exists as to the roles of intercropped legumes in the rhizosphere microbiome and tea quality. Hereby, soybean was selected as the intercropped plant to investigate its effect on bacterial communities, nutrient competition, tea plant development, and tea quality. Our data showed that intercropped soybean boosted the uptake of nitrogen in tea plants and enhanced the growth of young tea shoots. Nutrient competition for phosphorus and potassium in soil existed between soybeans and tea plants. Moreover, tea/soybean intercropping improved tea quality, manifested by a significantly increased content of non-ester type catechins (C, EGC, EC), total catechins and theanine, and decreased content of ester type catechins (EGCG). Significant differences in rhizobacterial composition were also observed under different systems. At the genus level, the relative abundance of beneficial bacteria, such as Bradyrhizobium, Saccharimonadales and Mycobacterium, was significantly increased with the intercropping system, while the relative abundance of denitrifying bacteria, Pseudogulbenkiania, was markedly decreased. Correlation analysis showed that Pseudogulbenkiania, SBR1031, and Burkholderiaceae clustered together showing a similar correlation with soil physicochemical and tea quality characteristics; however, other differential bacteria showed the opposite pattern. In conclusion, tea/soybean intercropping improves tea quality and nutrition uptake by increasing the relative abundance of beneficial rhizosphere bacteria and decreasing denitrifying bacteria. This study strengthens our understanding of how intercropping system regulate the soil bacterial community to maintain the health of soils in tea plantations and provides the basis for replacing chemical fertilizers and improving the ecosystem in tea plantations.

Network and meta-omics reveal the cooperation patterns and mechanisms in an efficient 1,4-dioxane-degrading microbial consortium

1,4-Dioxane is an emerging wastewater contaminant with probable human carcinogenicity. Our current understanding of microbial interactions during 1,4-dioxane biodegradation process in mixed cultures is limited. Here, we applied metagenomic, metatranscriptomic and co-occurrence network analyses to unraveling the microbial cooperation between degrader and non-degraders in an efficient 1,4-dioxane-degrading microbial consortium CH1. A 1,4-dioxane-degrading bacterium, Ancylobacter polymorphus ZM13, was isolated from CH1 and had a potential of being one of the important degraders due to its high relative abundance, highly expressed monooxygenase genes tmoABCDEF and high betweenness centrality of networks. The strain ZM13 cooperated obviously with 6 bacterial genera in the network, among which Xanthobacter and Mesorhizobium could be involved in the intermediates metabolism with responsible genes encoding alcohol dehydrogenase (adh), aldehyde dehydrogenase (aldh), glycolate oxidase (glcDEF), glyoxylate carboligase (gcl), malate synthase (glcB) and 2-isopropylmalate synthase (leuA) differentially high-expressed. Also, 1,4-dioxane facilitated the shift of biodiversity and function of CH1, and those cooperators cooperated with ZM13 in the way of providing amino acids or fatty acids, as well as relieving environmental stresses to promote biodegradation. These results provide new insights into our understandings of the microbial interactions during 1,4-dioxane degradation, and have important implications for predicting microbial cooperation and constructing efficient and stable synthetic 1,4-dioxane-degrading consortia for practical remediation.

Influence of nitrate concentration on trichloroethylene reductive dechlorination in weak electric stimulation system

The co-existence of volatile chlorinated hydrocarbons (VCHs) and nitrate pollution in groundwater is prominent, but how nitrate exposure affects weak-electrical stimulated bio-dechlorination activity of VCH is largely unknown. Here, by establishing weak-electrical stimulated trichloroethylene (TCE) dechlorination systems, the influence on TCE dechlorination by exposure to the different concentrations (25-100 mg L^-1) of nitrate was investigated. The existence of nitrate in general decreased TCE dechlorination efficiency to varying degrees, and the higher nitrate concentration, the stronger the inhibitory effects, verified by the gradually decreased transcription levels of tceA. Although the TCE dechlorination kinetic rate constant decreased by 36% the most, under all nitrate concentration ranges, TCE could be completely removed within 32 h and no difference in generated metabolites was found, revealing the well-maintained dechlorination activity. This was due to the quickly enriched bio-denitrification activity, which removed nitrate completely within 9 h, and thus relieved the inhibition on TCE dechlorination. The obvious bacterial community structure succession was also observed, from dominating with dechlorination genera (e.g., Acetobacterium, Eubacterium) to dominating with both dechlorination and denitrification genera (e.g., Acidovorax and Brachymonas). The study proposed the great potential for the in situ simultaneous denitrification and dehalogenation in groundwater contaminated with both nitrate and VCHs.

Selective pressure on microbial communities in a drinking water aquifer - Geochemical parameters vs. micropollutants

Groundwater quality is crucial for drinking water production, but groundwater resources are increasingly threatened by contamination with pesticides. As pesticides often occur at micropollutant concentrations, they are unattractive carbon sources for microorganisms and typically remain recalcitrant. Exploring microbial communities in aquifers used for drinking water production is an essential first step towards understanding the fate of micropollutants in groundwater. In this study, we investigated the interaction between groundwater geochemistry, pesticide presence, and microbial communities in an aquifer used for drinking water production. Two groundwater monitoring wells in The Netherlands were sampled in 2014, 2015, and 2016. In both wells, water was sampled from five discrete depths ranging from 13 to 54 m and was analyzed for geochemical parameters, pesticide concentrations and microbial community composition using 16S rRNA gene sequencing and qPCR. Groundwater geochemistry was stable throughout the study period and pesticides were heterogeneously distributed at low concentrations (μg L^-1 range). Microbial community composition was also stable throughout the sampling period. Integration of a unique dataset of chemical and microbial data showed that geochemical parameters and to a lesser extent pesticides exerted selective pressure on microbial communities. Microbial communities in both wells showed similar composition in the deeper aquifer, where pumping results in horizontal flow. This study provides insight into groundwater parameters that shape microbial community composition. This information can contribute to the future implementation of remediation technologies to guarantee safe drinking water production.

Stabilization of lead and cadmium in soil by sulfur-iron functionalized biochar: Performance, mechanisms and microbial community evolution

Sulfur-iron functionalized biochar (BC-Fe-S) was designed by simultaneously supporting Fe₂O₃ nanoparticles and grafting sulfur-containing functional groups onto biochar to stabilize Pb and Cd in soil. The BC-Fe-S exhibited excellent stabilization performance for Pb and Cd with fast kinetic equilibrium within 5 days associating with pseudo-second-order model. The bioavailable-Pb and -Cd contents decreased by 59.22% and 70.28% with 3% BC-Fe-S treatment after 20 days of remediation. Speciation transformation analysis revealed that the increase of stabilization time and BC-Fe-S dosage with appropriate soil moisture and pH promoted toxicities decrease of Pb and Cd with transformation of labile fractions to more steady fractions. The labile fractions of Pb and Cd decreased by 12.22% and 16.21% with 3% BC-Fe-S treatment, and transformed to the residual speciation. Meanwhile, wetting-drying and freezing-thawing aging did not markedly alter the bioavailability of Pb and Cd, proving that the BC-Fe-S holds promise for stabilization of Pb and Cd in varying environmental conditions. 16S rRNA sequencing analysis demonstrated that the BC-Fe-S significantly improved diversity and composition of microbial community, especially increasing the relative abundance of heavy metal-resistant bacteria. Overall, these results suggested BC-Fe-S as a high-performance and environmental-friendly amendment with stability to remediate heavy metals polluted soil.

Recent Developments in Advanced Oxidation Processes for Organics-Polluted Soil Reclamation

Soil pollution has become a substantial environmental problem which is amplified by overpopulation in different regions. In this review, the state of the art regarding the use of Advanced Oxidation Processes (AOPs) for soil remediation is presented. This review aims to provide an outline of recent technologies developed for the decontamination of polluted soils by using AOPs. Depending on the decontamination process, these techniques have been presented in three categories: the Fenton process, sulfate radicals process, and coupled processes. The review presents the achievements of, and includes some reflections on, the status of these emerging technologies, the mechanisms, and influential factors. At the present, more investigation and development actions are still desirable to bring them to real full-scale implementation.

Perturbation of clopyralid on bio-denitrification and nitrite accumulation: Long-term performance and biological mechanism

The contaminant of herbicide clopyralid (3,6-dichloro-2- pyridine-carboxylic acid, CLP) poses a potential threat to the ecological system. However, there is a general lack of research devoted to the perturbation of CLP to the bio-denitrification process, and its biological response mechanism remains unclear. Herein, long-term exposure to CLP was systematically investigated to explore its influences on denitrification performance and dynamic microbial responses. Results showed that low-concentration of CLP (<15 mg/L) caused severe nitrite accumulation initially, while higher concentrations (35-60 mg/L) of CLP had no further effect after long-term acclimation. The mechanistic study demonstrated that CLP reduced nitrite reductase (NIR) activity and inhibited metabolic activity (carbon metabolism and nitrogen metabolism) by causing oxidative stress and membrane damage, resulting in nitrite accumulation. However, after more than 80 days of acclimation, almost no nitrite accumulation was found at 60 mg/L CLP. It was proposed that the secretion of extracellular polymeric substances (EPS) increased from 75.03 mg/g VSS at 15 mg/L CLP to 109.97 mg/g VSS at 60 mg/L CLP, which strengthened the protection of microbial cells and improved NIR activity and metabolic activities. Additionally, the biodiversity and richness of the microbial community experienced a U-shaped process. The relative abundance of denitrification- and carbon metabolism-associated microorganisms decreased initially and then recovered with the enrichment of microorganisms related to the secretion of EPS and N-acyl-homoserine lactones (AHLs). These microorganisms protected microbe from toxic substances and regulated their interactions among inter- and intra-species. This study revealed the biological response mechanism of denitrification after successive exposure to CLP and provided proper guidance for analyzing and treating herbicide-containing wastewater.

Identification of the phylotypes involved in cis-dichloroethene and 1,4-dioxane biodegradation in soil microcosms

Co-contamination with chlorinated compounds and 1,4-dioxane has been reported at many sites. Recently, there has been an increased interest in bioremediation because of the potential to degrade multiple contaminants concurrently. Towards improving bioremediation efficacy, the current study examined laboratory microcosms (inoculated separately with two soils) to determine the phylotypes and functional genes associated with the biodegradation of two common co-contaminants (cis-dichloroethene [cDCE] and 1,4-dioxane). The impact of amending microcosms with lactate on cDCE and 1,4-dioxane biodegradation was also investigated. The presence of either lactate or cDCE did not impact 1,4-dioxane biodegradation one of the two soils. Lactate appeared to improve the initiation of the biological removal of cDCE in microcosms inoculated with either soil. Stable isotope probing (SIP) was then used to determine which phylotypes were actively involved in carbon uptake from cDCE and 1,4-dioxane in both soil communities. The most enriched phylotypes for ¹³C assimilation from 1,4-dioxane included Rhodopseudomonas and Rhodanobacter. Propane monooxygenase was predicted (by PICRUSt2) to be dominant in the 1,4-dioxane amended microbial communities and propane monooxygenase gene abundance values correlated with other enriched (but less abundant) phylotypes for ¹³C-1,4-dioxane assimilation. The dominant enriched phylotypes for ¹³C assimilation from cDCE included Bacteriovorax, Pseudomonas and Sphingomonas. In the cDCE amended soil microcosms, PICRUSt2 predicted the presence of DNA encoding glutathione S-transferase (a known cDCE upregulated enzyme). Overall, the work demonstrated concurrent removal of cDCE and 1,4-dioxane by indigenous soil microbial communities and the enhancement of cDCE removal by lactate. The data generated on the phylotypes responsible for carbon uptake (as determined by SIP) could be incorporated into diagnostic molecular methods for site characterization. The results suggest concurrent biodegradation of cDCE and 1,4-dioxane should be considered for chlorinated solvent site remediation.

Micro-bubbles enhanced removal of diesel oil from the contaminated soil in washing/flushing with surfactant and additives

Diesel removal of contaminated soil by washing/flushing was enhanced with micro-bubbles and selected surfactants based on their solubilization properties and decontamination capacities. The influencing factors were studied to aim for increasing washing/flushing efficacy. The mixture solution of saponin and cyclodextrin increased the removal efficiency significantly compared to the single-agent solution flushing with an increasing range of 20%-31%. Meanwhile, micro-bubble enhancement increased over 20% of the diesel removal for the sandy soil flushing. As the flushing process may cause soil eroded, the TDS and soil solute in flushing solution were measured to evaluate the circulation time. The 90 min flushing time ensured the cleaning goal and reserved the soil solute by circulation flushing. The soil solute, especially the electron acceptor (NO₃^-) , was remained in the soil, which was highly demanded for residual diesel biodegradation of loam soil. It is concluded that mixed agents, circulation of flushing solution, and micro-bubbles increased the diesel removal, and the circulation flushing could be very promising in practical applications.

Effects of microbial inactivation approaches on quantity and properties of extracellular polymeric substances in the process of wastewater treatment and reclamation: A review

Microbial extracellular polymeric substances (EPS) have a profound role in various wastewater treatment and reclamation processes, in which a variety of technologies are used for disinfection and microbial growth inhibition. These treatment processes can induce significant changes in the quantity and properties of EPS, and altered EPS could further adversely affect the wastewater treatment and reclamation system, including membrane filtration, disinfection, and water distribution. To clarify the effects of microbial inactivation approaches on EPS, these effects were classified into four categories: (1) chemical reactions, (2) cell lysis, (3) changing EPS-producing metabolic processes, and (4) altering microbial community. Across these different effects, treatments with free chlorine, methylisothiazolone, TiO₂, and UV irradiation typically enhance EPS production. Among the residual microorganisms in EPS matrices after various microbial inactivation treatments, one of the most prominent is Mycobacterium. With respect to EPS properties, proteins and humic acids in EPS are usually more susceptible to treatment processes than polysaccharides. The affected EPS properties include changes in molecular weight, hydrophobicity, and adhesion ability. All of these changes can undermine wastewater treatment and reclamation processes. Therefore, effects on EPS quantity and properties should be considered during the application of microbial inactivation and growth inhibition techniques.

Identification of novel 1,4-dioxane degraders and related genes from activated sludge by taxonomic and functional gene sequence analysis

This study used integrated omics technologies to investigate the potential novel pathways and enzymes for 1,4-dioxane degradation by a consortium enriched from activated sludge of a domestic wastewater treatment plant. An unclassified genus belonging to Xanthobacteraceae increased significantly after magnetic nanoparticle-mediated isolation for 1,4-dioxane degraders. Species with relatively higher abundance (> 0.3%) were identified to present high metabolic activities in the biodegradation process through shotgun sequencing. The functional gene investigations revealed that Xanthobacter sp. 91, Xanthobacter sp. 126, and a Rhizobiales strain carried novel 1,4-dioxane-hydroxylating monooxygenase genes. Xanthobacter sp. 126 contained the genes coding for glycolate oxidase, which was the main enzyme responsible for utilization of 1,4-dioxane intermediates through the TCA cycle, and further proven by the specific glycolate oxidase inhibitor, α-hydroxy-2-pyridinemethanesulfonic acid. An expanded and detailed degradation pathway of 1,4-dioxane was proposed on the basis of the three major intermediates (2-hydroxy-1,4-dioxane, ethylene glycol, and oxalic acid) confirmed by metabolomics. These findings of microbial community and function as well as the novel pathway will be valuable in predicting natural attenuation or reconstruction of a bacterial consortium for enhanced remediation of 1,4-dioxane-contaminated sites as well as wastewater treatment.

Enhanced degradation of 4-aminobenzenesulfonate by a co-culture of Afipia sp. 624S and Diaphorobacter sp. 624L

Two strains, Afipia sp. 624S and Diaphorobacter sp. 624L, were isolated from an enrichment culture with 4-aminobenzenesulfonate (4-ABS) as the only carbon source. Strain 624S utilized 4-ABS as the only source of carbon and energy and degraded 3.8 mM 4-ABS in 2 weeks, releasing a small amount of sulfate ions. On the other hand, strain 624L did not utilize 4-ABS. Additionally, a co-culture of strains 624S and 624L resulted in the enhanced degradation of 4-ABS, and no sulfite was accumulated in the degradation of 4-ABS. When incubated in 50 mM Tris-HCl buffer (pH 8.0) containing 2.2 mM sodium sulfite, strain 624S exhibited no sulfite oxidation; however, strain 624L completely oxidized the sulfite after 2 days. Furthermore, when manganase, which has the ability to oxidize sulfite, was added to the medium, the degradation rate of 4-ABS was increased in comparison with the non-addition control. These results indicate that the sulfite oxidation might stimulate the degradation of 4-ABS by strain 624S, suggesting syntrophic interaction between strains 624S and 624L based on sulfite oxidation.

Profiling microbial community structures and functions in bioremediation strategies for treating 1,4-dioxane-contaminated groundwater

Microbial community compositions and functional profiles were analyzed in microcosms established using aquifer materials from a former automobile factory site, where 1,4-dioxane was identified as the primary contaminant of concern. Propane or oxygen biostimulation resulted in limited 1,4-dioxane degradation, which was markedly enhanced with the addition of nutrients, resulting in abundant Mycobacterium and Methyloversatilis taxa and high expressions of propane monooxygenase gene, prmA. In bioaugmented treatments, Pseudonocardia dioxanivorans CB1190 or Rhodococcus ruber ENV425 strains dominated immediately after augmentation and degraded 1,4-dioxane rapidly which was consistent with increased representation of xenobiotic and lipid metabolism-related functions. Although the bioaugmented microbes decreased due to insufficient growth substrates and microbial competition, they did continue to degrade 1,4-dioxane, presumably by indigenous propanotrophic and heterotrophic bacteria, inducing similar community structures across bioaugmentation conditions. In various treatments, functional redundancy acted as buffer capacity to ensure a stable microbiome, drove the restoration of the structure and microbial functions to original levels, and induced the decoupling between basic metabolic functions and taxonomy. The results of this study provided valuable information for design and decision-making for ex-situ bioreactors and in-situ bioremediation applications. A metagenomics-based understanding of the treatment process will enable efficient and accurate adjustments when encountering unexpected issues in bioremediation.

Successful remediation of soils with mixed contamination of chromium and lindane: Integration of biological and physico-chemical strategies

Soils contaminated by organic and inorganic pollutants like Cr(VI) and lindane, is currently a main environmental challenge. Biological strategies, such as biostimulation, bioaugmentation, phytoremediation and vermiremediation, and nanoremediation with nanoscale zero-valent iron (nZVI) are promising approaches for polluted soil health recovery. The combination of different remediation strategies might be key to address this problem. For this reason, a greenhouse experiment was performed using soil without or with an organic amendment. Both soils were contaminated with lindane (15 mg kg^-1) and Cr(VI) (100 or 300 mg kg^-1). After one month of aging, the following treatments were applied: (i) combination of bioaugmentation (actinobacteria), phytoremediation (Brassica napus), and vermiremediation (Eisenia fetida), or (ii) nanoremediation with nZVI, or (iii) combination of biological treatments and nanoremediation. After 60 days, the wellness of plants and earthworms was assessed, also, soil health was evaluated through physico-chemical parameters and biological indicators. Cr(VI) was more toxic and decreased soil health, however, it was reduced to Cr(III) by the amendment and nZVI and, to a lesser extent, by the biological treatment. Lindane was more effectively degraded through bioremediation. In non-polluted soils, nZVI had strong deleterious effects on soil biota when combined with the organic matter, but this effect was reverted in soils with a high concentration of Cr(VI). Therefore, under our experimental conditions bioremediation might be the best for soils with a moderate concentration of Cr(VI) and organic matter. The application of nZVI in soils with a high content of organic matter should be avoided except for soils with very high concentrations of Cr(VI). According to our study, among the treatments tested, the combination of an organic amendment, biological treatment, and nZVI was shown to be the strategy of choice in soils with high concentrations of Cr(VI) and lindane, while for moderate levels of chromium, the organic amendment plus biological treatment is the most profitable treatment.

Characterization of 1,4-Dioxane Biodegradation by a Microbial Community

In this study, a microbial community of bacteria was investigated for 1,4-dioxane(1,4-D) biodegradation. The enriched culture was investigated for 1,4-dioxane mineralization, co-metabolism of 1,4-dioxane and extra carbon sources, and characterized 1,4-dioxane biodegradation kinetics. The mineralization test indicates that the enriched culture was able to degrade 1,4-dioxane as the sole carbon and energy source. Interestingly, the distribution of 1,4-dioxane into the final biodegrading products were 36.9% into biomass, 58.3% completely mineralized to CO2, and about 4% escaped as VOC. The enriched culture has a high affinity with 1,4-dioxane during biodegradation. The kinetic coefficients of the Monod equation were qmax = 0.0063 mg 1,4-D/mg VSS/h, Ks = 9.42 mg/L, YT = 0.43 mg VSS/mg 1,4-dioxane and the decay rate was kd = 0.023 mg/mg/h. Tetrahydrofuran (THF) and ethylene glycol were both consumed together with 1,4-dioxane by the enriched culture; however, ethylene glycol did not show any influence on 1,4-dioxane biodegradation, while THF proved to be a competitive.

Simultaneously enhanced surfactant flushing of diesel contaminated soil column and qualified emission of effluent

Seven surfactants were selected as candidate agents for in situ soil column flushing. Column flushing lacks the interaction between surfactants and contaminants, so efficiency is not easy to improve. Microbubbles generated in situ may adhere to the contaminant diesel. Thereafter, the bubbles were mobilized to lift the multi-system oil to the top layer. This process must be attributed to the increased column flushing efficiency of diesel removal. Compared with a single solution, using randomly methylated beta-cyclodextrin (RAMEB) and microbubble enhancement, the diesel removal of column flushing increased by 30.7%. Compared with the existing conditions (5.25 × 10^-4cm s^-1), the hydraulic conductivity of loam soil (3.74 × 10^-3cm s^-1) increased by 7.1 times after the continued operation of the two processes. The oil layer was collected for further reuse. After three treatments, the effluent for the RAMEB was more than 85%. The collected effluent was treated with a synthetic absorbent and then qualifiedly discharged with a TOC value of only 2.6 mg L^-1. By combining surfactant flushing with microbubbles and other equipment, not only can the reaction time be effectively saved, but organic pollutants could be concentrated and reused in the soil, so no additional treatment was required.

Effects of Additional Carbon Sources in the Biodegradation of 1,4-Dioxane by a Mixed Culture

A mixed culture utilizing 1,4-dioxane as a sole carbon and energy source was obtained from the activated sludge at a textile wastewater treatment plant. The biodegradation of 1,4-dioxane was characterized by a model based on the Monod equation. The effects of the presence of easily degradable carbon sources other than 1,4-dioxane were investigated using dextrose. Structural analogs commonly found in 1,4-dioxane-containing wastewater such as tetrahydrofuran (THF), 2-methyl-1,3-dioxolane, and 1,4-dioxene were also evaluated for their potential effects on 1,4-dioxane biodegradation. The presence of dextrose did not show any synergetic or antagonistic effects on 1,4-dioxane biodegradation, while the structural analogs showed significant competitive inhibition effects. The inhibitory effects were relatively strong with heptagonal cyclic ethers such as THF and 2-methyl-1,3-dioxolane, and mild with hexagonal cyclic ethers such as 1,4-dioxene. It was also shown that the treatment of 1,4-dioxane in the raw textile wastewater required 170% more time to remove 1,4-dioxane due to the co-presence of 2-methyl-1,3-dioxolane, and the extent of delay depended on the initial concentration of 1,3-doxolane.

Effect of salt and metal accumulation on performance of membrane distillation system and microbial community succession in membrane biofilms

Membrane distillation (MD) works as a potential technology for the "zero liquid discharge" water treatment owing to its high concentration brine tolerance. The continuous accumulation of salts and metals in the MD system during the "zero liquid discharge" water treatment inevitably posed remarkable impacts on the biofilm formation as well as the MD performance. Hence, the biofouling mechanism of MD was deeply researched in this study with an emphasis on the roles of salt-stress (NaCl) and metal-stress (Zn and Fe) in biofilm development. The membrane flux decline of MD was effectively mitigated by the appearance of NaCl and ZnO, while that was significantly aggravated under the metal-stress of Fe. Considering the serious membrane scaling caused by NaCl crystals, a sharp flux decline was seen for the NaCl group during the later stage of MD operation. Basing on the 16S rDNA and 16S rRNA analysis, heat-stress, salt-stress, and metal-stress all posed certain impacts on the biofouling development in the MD system, and a more remarkable influence was observed for metal-stress. Under the salt-stress from NaCl, a thin biofilm containing high biovolume of dead cells finally formed, in which the bacterial community mainly consisted of halotolerant and thermophile species. Owing to the Zn²⁺-stress and oxidation-stress mechanisms of ZnO, the bacteria in the MD system were largely dead and live bacterial community in biofilms was dominated by some gram-negative species. Under the metal-stress from Fe, a rather thick biofilm containing higher biovolume of live cells clearly developed, in which the prevailing species could secret large amounts of EPS and accumulate metabolites around cells as biological surfactants, inducing aggravated membrane biofouling and high risk of membrane wetting.

Variations of rhizospheric soil microbial communities in response to continuous Andrographis paniculata cropping practices

BACKGROUND

Changes of soil microbial communities are one of the main factors of continuous cropping problem. Andrographis paniculata has been reported to have replant problem in cultivation. However, little is known about the variations of rhizosphere soil microbial communities of A. paniculata under a continuous cropping system. Here, Illumina MiSeq was used to investigate the shifts of rhizospheric bacterial and fungal communities after continuous cropping of A. paniculata.

RESULTS

The bacterial diversity increased whereas the fungal diversity decreased in rhizosphere soil after consecutive A. paniculata monoculture; and the soil microbial community structure differed between newly plant soil and continuous cropped soil. Taxonomic analyses further revealed that the bacterial phyla Proteobacteria, Acidobacteria and Bacteroidetes and the fungal phyla Zygomycota, Ascomycota and Cercozoa were the dominant phyla across all soil samples. The relative abundance of phyla Acidobacteria and Zygomycota were significantly increased after continuous cropping. Additionally, the most abundant bacterial genus Pseudolabrys significantly decreased, while the predominant fungal genus Mortierella increased considerably in abundance after continuous cropping.

CONCLUSIONS

Our results revealed the changes on diversity and composition of bacterial and fungal communities in rhizospheric soil under continuous cropping of A. paniculata. These data contributed to the understanding of soil micro-ecological environments in the rhizosphere of A. paniculata.

Monitoring, assessment, and prediction of microbial shifts in coupled catalysis and biodegradation of 1,4-dioxane and co-contaminants

Microbial community dynamics were characterized following combined catalysis and biodegradation treatment trains for mixtures of 1,4-dioxane and chlorinated volatile organic compounds (CVOCs) in laboratory microcosms. Although a few specific bacterial taxa are capable of removing 1,4-dioxane and individual CVOCs, many microorganisms are inhibited when these contaminants are present in mixtures. Chemical catalysis by tungstated zirconia (WO_x/ZrO₂) and hydrogen peroxide (H₂O₂) as a non-selective treatment was designed to achieve nearly 20% 1,4-dioxane and over 60% trichloroethene and 50% dichloroethene removals. Post-catalysis, bioaugmentation with 1,4-dioxane metabolizing bacterial strain,Pseudonocardia dioxanivorans CB1190, removed the remaining 1,4-dioxane. The evolution of the microbial community under different conditions was time-dependent but relatively independent of the concentrations of contaminants. The compositions of microbiomes tended to be similar regardless of complex contaminant mixtures during the biodegradation phase, indicating a r-K strategy transition attributed to the shock experienced during catalysis and the subsequent incubation. The originally dominant genera Pseudomonas and Ralstonia were sensitive to catalytic oxidation, and were overwhelmed by Sphingomonas, Rhodococcus, and other catalyst-tolerant microbes, but microbes capable of biodegradation of organics thrived during the incubation. Methane metabolism, chloroalkane-, and chloroalkene degradation pathways appeared to be responsible for CVOC degradation, based on the identifications of haloacetate dehalogenases, 2-haloacid dehalogenases, and cytochrome P450 family. Network analysis highlighted the potential interspecies competition or commensalism, and dynamics of microbiomes during the biodegradation phase that were in line with shifting predominant genera, confirming the deterministic processes guiding the microbial assembly. Collectively, this study demonstrated that catalysis followed by bioaugmentation is an effective treatment for 1,4-dioxane in the presence of high CVOC concentrations, and it enhanced our understanding of microbial ecological impacts resulting from abiotic-biological treatment trains. These results will be valuable for predicting treatment synergies that lead to cost savings and improve remedial outcomes in short-term active remediation as well as long-term changes to the environmental microbial communities.

Change of abundance and correlation of Nitrospira inopinata-like comammox and populations in nitrogen cycle during different seasons

Complete-nitrifying bacteria (comammox) play important roles in nitrogen-overloading aquatic systems. However, the understanding of the environmental relevance is still limited. Here, we studied the responses of comammox bacteria (Nitrospira inopinata) in a tributary of the Yellow River, with the water and sediment, microbial, seasonal, and chemical variations considered. Illumina sequencing indicated that the predominant phyla in the river sediment were Proterobacteria, Bacteroidetes, Actinobacteria, and Chloroflex. Quantitative PCR revealed that N. inopinata-like comammox were approximately twice as abundant in the water during the wet season and in the sediment during the dry season than that of other conditions. Significant correlations were found between the abundance of N. inopinata-like comammox and pH (r = 0.58), temperature (r = 0.63), and dissolved oxygen (r = - 0.77). The abundance of N. inopinata-like comammox was higher than that of ammonia oxidizing archaea (AOA), and lower than that of ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB). Furthermore, a significant correlation was discovered between N. inopinata-like comammox and NOB (r = 0.60), and so was anammox bacteria (r = 0.358). Interestingly, N. inopinata-like comammox also showed positive relationships with denitrifying microbes (r = 0.559).

Mechanisms of 1,4-Dioxane Biodegradation and Adsorption by Bio-Zeolite in the Presence of Chlorinated Solvents: Experimental and Molecular Dynamics Simulation Studies

The use of bioaugmented zeolite (bio-zeolite) can be an effective technology for irreversibly removing recalcitrant organic pollutants in aqueous mixtures. Removal of 1,4-dioxane by a bio-zeolite (Pseudonocardia dioxanivorans CB1190-bioaugmented ZSM-5) in the presence of several chlorinated volatile organic compounds (CVOCs) was superior to removal by adsorption using abiotic zeolite. Mixtures containing 1,1-dichloroethene (1,1-DCE) were an exception, which completely inhibited the bio-zeolite system. Specific adsorption characteristics were studied using adsorption isotherms in single-solute and bisolute systems accompanied by Polanyi theory-based Dubinin-Astakhov (DA) modeling. Adsorption behavior was examined using characteristic energy (E_a/H) from modified DA models and molecular dynamics simulations. While the tight-fit of 1,4-dioxane in the hydrophobic channels of ZSM-5 appears to drive 1,4-dioxane adsorption, the greater hydrophobicity of trichloroethene and cis-1,2-dichloroethene cause them have a greater affinity over 1,4-dioxane for adsorption sites on the zeolite. 1,4-Dioxane was desorbed and displaced by CVOCs except 1,1-DCE because of its low E_a/H value, explaining why bio-zeolite only biodegraded 1,4-dioxane in 1,1-DCE-free CVOC mixtures. Understanding the adsorption mechanisms of solutes in complex mixtures is crucial for the implementation of sorption-based treatment technologies for the removal of complex contaminant mixtures from aquatic environments.