Significance of non-DLVO interactions on the co-transport of levofloxacin and titanium dioxide nanoparticles in porous media.

With the application of engineered nanomaterials and antibiotics in the fields of medicine, aerospace, new energy and agriculture, the associated contamination is detected widely in soil-groundwater systems. It is of great scientific and practical significance to deeply explore the environmental interface process between nanoparticles and antibiotics for the scientific assessment of environmental fate and ecological environmental risks, as well as the development of new composite pollution control technologies. In this study, the co-transport behaviors of positively charged titanium dioxide nanoparticles (TiO2-NPs) and negatively charged levofloxacin (LEV) in quartz sand (QS) are investigated in this study. The results show that TiO2-NPs hardly flow out when transported alone in the column because of its positive charge, which creates a strong attraction with the negatively charged quartz sand on the surface. When TiO2-NPs co-migrate with LEV in porous media, the presence of LEV promotes the transport of TiO2-NPs, while the presence of TiO2-NPs inhibits LEV transport. Non-XDLVO interactions based on molecular dynamics (MD) simulations can help explain the observed promotion and inhibition phenomena as well as the correlation between TiO2-NPs and LEV. The results indicate that TiO2-LEV complexes or aggregates can be formed during the co-transportation process of TiO2-NPs and LEV in porous media. As flow velocity increases from 0.204 cm min-1 to 1.630 cm min-1, both the transport capacities of TiO2-NPs and LEV are enhanced significantly. Under the condition of high citric acid (CA) concentration (15 mmol L-1), the transport capacity of TiO2-NPs is slightly inhibited, while the transport capacity of LEV is enhanced. This study provides new insights into the transport of nanometallic oxides and antibiotics in porous media, which suggests that non-XDLVO interactions should be considered together when assessing the environmental risks and fate of nanometallic oxides and antibiotics in soil-groundwater systems.

Congener-specific fate and impact of microcystins in the soil-earthworm system.

Microcystins (MCs) have a significant influence on aquatic ecosystems, but little is known about their terrestrial fate and impact. Here, we investigated the fate of two MCs (MC-LR and MC-RR) in the soil-earthworm system, with consideration of their congener-specific impact on earthworm health, soil bacteria, and soil metabolome. Although MCs had little acute lethal effect on earthworms, they caused obvious growth inhibition and setae rupture. Relative to MC-RR, MC-LR exhibited higher bioaccumulation and the resulting dermal lesions and deformation of longitudinal muscles. While the incorporation of both MCs into soils stimulated pathogenic bacteria and depressed oxidative stress tolerant bacteria, the response among soil nitrification and glutathione metabolism differed between the two congeners. The dissipation kinetics of MCs obeyed the first-order model. Earthworms stimulated soil N-cycling enzyme activities, increased the abundance of MC-degrading bacteria, and promoted bacterial metabolic functions related to glutathione metabolism, xenobiotics biodegradation, and metabolism of amino acids that comprise MCs, which accelerated the dissipation of MC-LR and MC-RR by 227% and 82%, respectively. These results provide evidence of significant congener differences in the terrestrial fate and impact of MCs, which will enable a better understanding of their role in mediating soil functions and ecosystem services.

Iron complex regulated synergistic effect between the current and peroxymonosulfate enhanced ultrafast oxidation of perfluorooctanoic acid via free radical dominant electrochemical reaction.

Iron complex regulated electrochemical reaction was triggered for revealing the reaction mechanism, degradation pathway, and applied potential of perfluorooctanoic acid (PFOA). The increased PMS concentrations, electrode spacing, and current density significantly enhanced PFOA elimination, with current density exhibiting a relatively strong interdependency to PFOA complete mineralization. The synergy between PMS and electrochemical reactions greatly accelerated PFOA decomposition by promoting the generation of key reaction sites, such as those for PMS activation and electrochemical processes, under various conditions. Furthermore, density functional theory calculations confirmed that the reciprocal transformation of Fe2+ and Fe3+ complexes was feasible under the electrochemical effect, further promoting the generation of active sites. The developed electrochemical oxidation with PMS reaction (EO/PMS) system can rapidly decompose and mineralize PFOA while maintaining strong tolerance to changing water matrices and organic and inorganic ions. Overall, it holds promise for use in treating and purifying wastewater containing PFOA.

Molecular insights into the catabolism of dibutyl phthalate in Pseudomonas aeruginosa PS1 based on biochemical and multi-omics approaches.

A comprehensive understanding of the molecular mechanisms underlying microbial catabolism of dibutyl phthalate (DBP) is still lacking. Here, we newly isolated a bacterial strain identified as Pseudomonas aeruginosa PS1 with high efficiency of DBP degradation. The degradation ratios of DBP at 100-1000 mg/L by this strain reached 80-99 % within 72 h without a lag phase. A rare DBP-degradation pathway containing two monobutyl phthalate-catabolism steps was proposed based on intermediates identified by HPLC-TOF-MS/MS. In combination with genomic and transcriptomic analyses, we identified 66 key genes involved in DBP biodegradation and revealed the genetic basis for a new complete catabolic pathway from DBP to Succinyl-CoA or Acetyl-CoA in the genus Pseudomonas for the first time. Notably, we found that a series of homologous genes in Pht and Pca clusters were simultaneously activated under DBP exposure and some key intermediate degradation related gene clusters including Pht, Pca, Xyl, Ben, and Cat exhibited a favorable coexisting pattern, which contributed the high-efficient DBP degradation ability and strong adaptability to this strain. Overall, these results broaden the knowledge of the catabolic diversity of DBP in microorganisms and enhance our understanding of the molecular mechanism underlying DBP biodegradation.

Biodegradation of phthalate acid esters and whole-genome analysis of a novel Streptomyces sp. FZ201 isolated from natural habitats.

Di-n-butyl phthalate (DBP) is one of the most extensively used phthalic acid esters (PAEs) and is considered to be an emerging, globally concerning pollutant. The genus Streptomyces holds promise as a degrader of various organic pollutants, but PAE biodegradation mechanisms by Streptomyces species remain unsolved. In this study, a novel PAE-degrading Streptomyces sp. FZ201 isolated from natural habitats efficiently degraded various PAEs. FZ201 had strong resilience against DBP and exhibited immediate degradation, with kinetics adhering to a first-order model. The comprehensive biodegradation of DBP involves de-esterification, ß-oxidation, trans-esterification, and aromatic ring cleavage. FZ201 contains numerous catabolic genes that potentially facilitate PAE biodegradation. The DBP metabolic pathway was reconstructed by genome annotation and intermediate identification. Streptomyces species have an open pangenome with substantial genome expansion events during the evolutionary process, enabling extensive genetic diversity and highly plastic genomes within the Streptomyces genus. FZ201 had a diverse array of highly expressed genes associated with the degradation of PAEs, potentially contributing significantly to its adaptive advantage and efficiency of PAE degradation. Thus, FZ201 is a promising candidate for remediating highly PAE-contaminated environments. These findings enhance our preliminary understanding of the molecular mechanisms employed by Streptomyces for the removal of PAEs.

Root-associated bacteria strengthen their community stability against disturbance of antibiotics on structure and functions.

Antibiotics affect bacterial community structure and functions in soil. However, the response and adaptation of root-associated bacterial communities to antibiotic stress remains poorly understood. Here, rhizobox experiments were conducted with maize (Zea mays L.) upon exposure to antibiotics ciprofloxacin or tetracycline. High-throughput sequencing analysis of bacterial community and quantitative PCR analysis of nitrogen cycling genes show that ciprofloxacin and tetracycline significantly shift bacterial community structure in bulk soil, whereas plant host may mitigate the disturbances of antibiotics on bacterial communities in root-associated niches (i.e., rhizosphere and rhizoplane) through the community stabilization. Deterministic assembly, microbial interaction, and keystone species (e.g., Rhizobium and Massilia) of root-associated bacterial communities benefit the community stability compared with those in bulk soil. Meanwhile, the rhizosphere increases antibiotic dissipation, potentially reducing the impacts of antibiotics on root-associated bacterial communities. Furthermore, rhizospheric effects deriving from root exudates alleviate the impacts of antibiotics on the nitrogen cycle (i.e., nitrification, organic nitrogen conversion and denitrification) as confirmed by functional gene quantification, which is largely attributed to the bacterial community stability in rhizosphere. The present study enhances the understanding on the response and adaptation of root-associated bacterial community to antibiotic pollution.

Activated DBP degradation and relevant signal transduction path via quorum sensing autoinducers in Streptomyces sp. SH5.

Microbe-mediated DBP (dibutyl phthalate) mineralization is acknowledged to be affected by diverse extracellular factors. However, little is known about the regulatory effects from quorum sensing (QS) signals. In this study, extracellularly applied QS signals A-like (hydroxymethyl dihydrofuran) was discovered to significantly enhance DBP degradation efficiency in Streptomyces sp. SH5. Monobutyl phthalate, protocatechuic acid and beta-ketoadipate were discovered as degradation intermediates by HPLC-TOF-MS/MS. Multi-omics analysis revealed the up-regulation of multiple hydrolases, transferases and decarboxylases that potentially contributed to A-like accelerated DBP degradation. Transcription of Orf2708, an orthologue of global transcriptional activator, was significantly induced by A-like. Orf2708 was demonstrated to interact specifically with the promoter of hydrolase orf2879 gene by EMSA, and the overexpression of orf2879 led to an enhanced DBP degradation in SH5. Taken together with the molecular docking studies showing the stability of ligand-receptor complex of A-like and its potential receptor Orf3712, a hierarchical regulatory cascade underlying the QS signal mediated DBP degradation was proposed as A-like/Orf3712 duplex formation, enhanced orf2708 expression and the downstream specific activation of hydrolase Orf2879. Our study presents the first evidence of GBLs-type promoted DBP degradation among bacteria, and the elucidated signal transduction path indicates a universal application potential of this activation strategy.

Insights into the molecular network underlying phytotoxicity and phytoaccumulation of ciprofloxacin.

Ciprofloxacin (CIP) is frequently detected in agricultural soils and can be accumulated by crops, causing phytotoxicities and food safety concerns. However, the molecular basis of its phytotoxicity and phytoaccumulation is hardly known. Here, we analyzed physiological and molecular responses of choysum (Brassica parachinensis) to CIP stress by comparing low CIP accumulation variety (LAV) and high accumulation variety (HAV). Results showed that the LAV suffered more severe inhibition of growth and photosynthesis than the HAV, exhibiting a lower tolerance to CIP toxicity. Integrated transcriptome and proteome analyses suggested that more differentially expressed genes/proteins (DEGs/DEPs) involved in basic metabolic processes were downregulated to a larger extent in the LAV, explaining its lower CIP tolerance at molecular level. By contrast, more DEGs/DEPs involved in defense responses were upregulated to a larger extent in the HAV, showing the molecular basis of its stronger CIP tolerance. Further, a CIP phytotoxicity-responsive molecular network was constructed for the two varieties to better understand the molecular mechanisms underlying the variety-specific CIP tolerance and accumulation. The results present the first comprehensive molecular profile of plant response to CIP stress for molecular-assisted breeding to improve CIP tolerance and minimize CIP accumulation in crops.

Response and adaptation of rhizosphere microbiome to organic pollutants with enriching pollutant-degraders and genes for bioremediation: A critical review.

Phytoremediation largely involves microbial degradation of organic pollutants in rhizosphere for removing organic pollutants like polycyclic aromatic hydrocarbons, phthalates and polychlorinated biphenyls. Microbial community in rhizosphere experiences complex processes of response-adaptation-feedback up on exposure to organic pollutants. This review summarizes recent research on the response and adaptation of rhizosphere microbial community to the stress of organic pollutants, and discusses the enrichment of the pollutant-degrading microbial community and genes in the rhizosphere for promoting bioremediation. Soil pollution by organic contaminants often reduces the diversity of rhizosphere microbial community, and changes its functions. Responses vary among rhizosphere microbiomes up on different classes of organic pollutants (including co-contamination with heavy metals), plant species, root-associated niches (e.g., rhizosphere, rhizoplane and endosphere), geographical location and soil properties. Soil pollution can deplete some sensitive microbial taxa and enrich some tolerant microbial taxa in rhizosphere. Furthermore, rhizosphere enriches pollutant-degrading microbial community and functional genes including different gene clusters responsible for biodegradation of organic pollutants and their intermediates, which improve the adaptation of microbiome and enhance the remediation efficiency of the polluted soil. The knowledge gaps and future research challenges are highlighted on rhizosphere microbiome in response-adaptation-feedback processes to organic pollution and rhizoremediation. This review will hopefully update understanding on response-adaptation-feedback processes of rhizosphere microbiomes and rhizoremediation for the soil with organic pollutants.

Mechanism and Association between Microbial Nitrogen Transformation in Rhizosphere and Accumulation of Ciprofloxacin in Choysum (Brassica parachinensis).

Rhizosphere microbiota are an important factor impacting plant uptake of pollutants. However, little is known about how microbial nitrogen (N) transformation in the rhizosphere affects the uptake and accumulation of antibiotics in plants. Here, we determined recruitment of N transformation functional bacteria upon ciprofloxacin (CIP) exposure, by comparing differences in assembly processes of both rhizospheric bacterial communities and N transformation between two choysum (Brassica parachinensis) varieties differing in CIP accumulation. The low accumulation variety (LAV) of CIP recruited more host bacteria (e.g., Nitrospiria and Nitrolancea) carrying nitrification genes (mainly nxrA) but fewer host bacteria carrying denitrification genes, especially narG, relative to the high accumulation variety (HAV) of CIP. The nxrA and narG abundance in the LAV rhizosphere were, respectively, 1.6-7.8 fold higher and 1.4-3.4 fold lower than those in the HAV rhizosphere. Considering that nitrate can decrease CIP uptake into choysum through competing for the proton motive force and energy, such specific bacteria recruitment in LAV favored the production and utilization of nitrate in its rhizosphere, thus limiting its CIP accumulation with 1.6-2.4 fold lower than the HAV. The findings give insight into the mechanism underlying low pollutant accumulation, filling the knowledge gap regarding the profound effects of rhizosphere microflora and N transformation processes on antibiotic accumulation in crops.

Highly Efficient and Simultaneous Analysis of Three Common Fluorotelomer Alcohols in Vegetables and Soils.

Fluorotelomer alcohols (FTOHs), as precursors of perfluoroalkyl carboxylic acids, are difficult to analyze due to their high volatility and matrix interference. A method based on single-factor experiments and response surface methodology design was developed for simultaneous analysis of three common FTOHs in vegetables and soils, using single extraction, dispersive solid phase extraction cleanup, and gas chromatography-mass spectrometry in negative chemical ionization. The method improved the extraction efficiency up to ∼40 folds and showed a commendable linearity range (1-100 ng/mL, R2 > 0.991), low limit of detection (0.025-0.897 ng/g, dry weight (dw)), and high accuracy and precision (83 ± 7.2-117 ± 6.0% recoveries at 2-20 ng/g fortification levels). It was successfully applied to determine the FTOHs in real vegetables and soils, demonstrating its feasibility for routine analysis. Concentrations of the FTOHs ranged from 3.5 to 37.9 ng/g (dw) and from 6.5 to 141.0 ng/g (dw), respectively, in the vegetables and soils collected nearby fluorochemical factories, which warrants further investigations on FTOH pollution and food safety concerns for which the developed method will be useful.

Quantification of two-site kinetic transport parameters of polystyrene nanoplastics in porous media.

In this study, a combination of column experiments, interface chemistry theory and transport model with two-site kinetics was used to systematically investigate the effect of pH on the transport of polystyrene nanoparticles (PSNPs) in porous media. The porous media containing quartz sand (QS) and three kinds of clay minerals (CMs)-kaolinite (KL), illite (IL) and montmorillonite (MT), was used in column experiments to simulate the porous media in the soil-groundwater systems. Experimental results showed that the inhibitory effect of CMs on the transport of PSNPs is weakened as pH increases. The two-dimensional (2D) surface of the DLVO interaction energy (2D-pH-DLVO) was built to calculate the interactions between PSNPs and CMs under different conditions of pH. Results suggested the inflection point of PSNP-QS, PSNP-KL, PSNP-IL and PSNP-MT are 2.42, 3.30, 2.84 and 3.69, respectively. Most importantly, there was a significant correlation between the two-site kinetic parameters related to PSNPs transport and the DLVO energy barrier (DB). The contributions of the interactions of PSNPs-PSNPs and PSNPs-minerals were determined for PSNPs transport in porous media. The critical values of pH related to the migration ability of PSNPs in porous media could be determined by a combination of column experiments, 2D-pH-DLVO and PSNPs transport model. The critical values of pH were 2.95-3.01, 3.22-3.51, 2.98-3.02, 3.31-3.33 for the migration ability of PSNPs in QS, QS + KL, QS + IL and QS + MT porous media, respectively. The stronger migration ability of PSNPs under high pH conditions is attributed to the enhanced deprotonation of the media surface and increased negative surface charge, which increases the electrostatic repulsion between PSNPs and porous media (QS, CMs). Moreover, the agglomeration of PSNPs usually is weaker and the average particle size of agglomerates is smaller under the condition of high pH, thus leading to the stronger migration ability of PSNPs under high pH conditions.

Substrate-enzyme interactions and catalytic mechanism in a novel family VI esterase with dibutyl phthalate-hydrolyzing activity.

Microbial degradation has been confirmed as effective and environmentally friendly approach to remediate phthalates from the environment, and hydrolase is an effective element for contaminant degradation. In the present study, a novel dibutyl phthalate (DBP)-hydrolyzing carboxylesterase (named PS06828) from Pseudomonas sp. PS1 was heterogeneously expressed in E. coli, which was identified as a new member of the lipolytic family VI. Purified PS06828 could efficiently degrade DBP with a wide range of temperature (25-37 °C) and pH (6.5-9.0). Multi-spectroscopy methods combined with molecular docking were employed to study the interaction of PS06828 with DBP. Fluorescence and UV-visible absorption spectra revealed the simultaneous presence of static and dynamic component in the fluorescence quenching of PS06828 by DBP. Synchronous fluorescence and circular dichroism spectra showed inconspicuous alteration in micro-environmental polarity around amino acid residues but obvious increasing of α-helix and reducing of ß-sheet and random coil in protein conformation. Based on the information on exact binding sites of DBP on PS06828 provided by molecular docking, the catalytic mechanism mediated by key residues (Ser113, Asp166, and His197) was proposed and subsequently confirmed by site-directed mutagenesis. The results can strengthen our mechanistic understanding of family VI esterase involved in hydrolysis of phthalic acid esters, and provide a solid foundation for further enzymatic modification.

Development, Evaluation, and Application of Machine Learning Models for Accurate Prediction of Root Uptake of Per- and Polyfluoroalkyl Substances.

Machine learning (ML) models were developed for understanding the root uptake of per- and polyfluoroalkyl substances (PFASs) under complex PFAS-crop-soil interactions. Three hundred root concentration factor (RCF) data points and 26 features associated with PFAS structures, crop properties, soil properties, and cultivation conditions were used for the model development. The optimal ML model, obtained by stratified sampling, Bayesian optimization, and 5-fold cross-validation, was explained by permutation feature importance, individual conditional expectation plot, and 3D interaction plot. The results showed that soil organic carbon contents, pH, chemical logP, soil PFAS concentration, root protein contents, and exposure time greatly affected the root uptake of PFASs with 0.43, 0.25, 0.10, 0.05, 0.05, and 0.05 of relative importance, respectively. Furthermore, these factors presented the key threshold ranges in favor of the PFAS uptake. Carbon-chain length was identified as the critical molecular structure affecting root uptake of PFASs with 0.12 of relative importance, based on the extended connectivity fingerprints. A user-friendly model was established with symbolic regression for accurately predicting RCF values of the PFASs (including branched PFAS isomerides). The present study provides a novel approach for profound insight into the uptake of PFASs by crops under complex PFAS-crop-soil interactions, aiming to ensure food safety and human health.

Bioremediation of aniline aerofloat wastewater at extreme conditions using a novel isolate Burkholderia sp. WX-6 immobilized on biochar.

Aniline aerofloat (AAF) is a refractory organic pollutant in floatation wastewater. Little information is currently available on its biodegradation. In this study, a novel AAF-degrading strain named Burkholderia sp. WX-6 was isolated from mining sludge. The strain could degrade more than 80% of AAF at different initial concentrations (100-1000 mg/L) within 72 h. AAF degrading curves were fitted well with the four-parameter logistic model (R2 >0.97), with the degrading half-life ranging from 16.39 to 35.55 h. This strain harbors metabolic pathway for complete degradation of AAF and is resistant to salt, alkali, and heavy metals. Immobilization of the strain on biochar enhanced both tolerance to extreme conditions and AAF removal, with up to 88% of AAF removal rate in simulated wastewater under alkaline (pH 9.5) or heavy metal pollution condition. In addition, the biochar-immobilized bacteria removed 59.4% of COD in the wastewater containing AAF and mixed metal ions within 144 h, significantly (P < 0.05) higher than those by free bacteria (42.6%) and biochar (48.2%) only. This work is helpful to understand AAF biodegradation mechanism and provides viable references for developing practical biotreatment technique of mining wastewater.

Rice genotypes and root-associated niches shifted bacterial community in response to pollution of di-(2-ethylhexyl) phthalate (DEHP) for promoting DEHP removal.

Organic pollutants influenced root-associated bacterial community. However, the response variation of root-associated bacterial community among different rice genotypes exposed to phthalates (PAEs) and their removal mechanism remains unknown. Here, bacterial community and PAE-degrading genes in root-associated niches were analyzed between low (Fengyousimiao) and high (Hhang) PAE-accumulating rice cultivars exposed to di-(2-ethylhexyl) phthalate (DEHP). DEHP dissipation percentages in rhizosphere of Hhang were significantly higher than those of Fengyousimiao. The bacterial community diversities (including Chao1 and Shannon index) significantly decreased along bulk soil - rhizosphere - rhizoplane - endosphere. The bacterial community structures were shaped mainly by root-associated niches, DEHP pollution and rice genotypes, with significant differences in rhizosphere and rhizoplane between Fengyousimiao and Hhang. Rhizosphere enriched more PAE-degrading bacteria than in bulk soil, and exhibited significantly higher expression of PAE-degrading genes (hydrolase 65, phtab, phtC, pcaF and pcaI) than in bulk soil. Furthermore, rhizosphere of Hhang demonstrated significantly stronger bacterial functions related to xenobiotics biodegradation and higher expression of PAE-degrading genes than those of Fengyousimiao, leading to significantly higher DEHP dissipation percentages in rhizosphere of Hhang. The findings demonstrate that Hhang shaped specific root-associated bacterial community with higher abundances of PAE-degrading bacteria and genes than Fengyousimiao to promote DEHP degradation.

Polyethylene and polypropylene microplastics reduce chemisorption of cadmium in paddy soil and increase its bioaccessibility and bioavailability.

Microplastics (MPs) usually coexist with heavy metals (HMs) in soil. MPs can influence HMs mobility and bioavailability, but the underlying mechanisms remain largely unexplored. Here, polyethylene and polypropylene MPs were selected to investigate their effects and mechanisms of sorption-desorption, bioaccessibility and bioavailability of cadmium (Cd) in paddy soil. Batch experiments indicated that MPs significantly reduced the Cd sorption in soil (p < 0.05). Accordingly, soil with the MPs had lower boundary diffusion constant of Cd (C1= 0.847∼1.020) and the Freundlich sorption constant (KF = 0.444-0.616) than that without the MPs (C1 = 0.894∼1.035, KF = 0.500-0.655). X-ray diffraction, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy analyses suggested that the MPs reduced Cd chemisorption, by covering the soil active sites and thus blocking complexation of Cd with active oxygen sites and interrupting the formation of CdCO3 and Cd3P2 precipitates. Such effects of MPs enhanced about 1.2-1.5 times of Cd bioaccessibility and bioavailability in soil. Almost the same effects but different mechanisms of polyethylene and polypropylene MPs on Cd sorption in the soil indicated the complexity and pervasiveness of their effects. The findings provide new insights into impacts of MPs on the fate and risk of HMs in agricultural soil.

Endophytic Phthalate-degrading Bacillus subtilis N-1-gfp colonizing in soil-crop system shifted indigenous bacterial community to remove di-n-butyl phthalate.

Endophytic bacteria can degrade toxic phthalate (PAEs). Nevertheless, the colonization and function of endophytic PAE-degrader in soil-crop system and their association mechanism with indigenous bacteria in PAE removal remain unknown. Here, endophytic PAE-degrader Bacillus subtilis N-1 was marked with green fluorescent protein gene. Inoculated strain N-1-gfp could well colonize in soil and rice plant exposed to di-n-butyl phthalate (DBP) as directly confirmed by confocal laser scanning microscopy and realtime PCR. Illumina high-throughput sequencing demonstrated that inoculated N-1-gfp shifted indigenous bacterial community in rhizosphere and endosphere of rice plants with significant increasing relative abundance of its affiliating genus Bacillus than non-inoculation. Strain N-1-gfp exhibited efficient DBP degradation with 99.7% removal in culture solutions, and significantly promoted DBP removal in soil-plant system. Strain N-1-gfp colonization help plant enrich specific functional bacteria (e.g., pollutant-degrading bacteria) with significant higher relative abundances and stimulated bacterial activities (e.g., pollutant degradation) compared with non-inoculation. Furthermore, strain N-1-gfp displayed strong interaction with indigenous bacteria for accelerating DBP degradation in soil, decreasing DBP accumulation in plants and promoting plant growth. This is the first report on well colonization of endophytic DBP-degrader Bacillus subtilis in soil-plant system and its bioaugmentation with indigenous bacteria for promoting DBP removal.

Phylogenetic Conservation of Soil Microbial Responses to Elevated Tropospheric Ozone and Nitrogen Fertilization.

Plant primary productivity and crop yields have been reduced due to the doubled level of global tropospheric ozone. Little is known about how elevated ozone affects soil microbial communities in the cropland ecosystem and whether such effects are sensitive to the nitrogen (N) supply. Here, we examined the responses of bacterial and fungal communities in maize soils to elevated ozone (+60 ppb ozone) across different levels of N fertilization (+60, +120, and +240 kg N ha-1yr-1). The fungal alpha diversity was decreased (P < 0.05), whereas the bacterial alpha diversity displayed no significant change under elevated ozone. Significant (P < 0.05) effects of N fertilization and elevated ozone on both the bacterial and fungal communities were observed. However, no interactive effects between N fertilization and elevated ozone were observed for bacterial and fungal communities (P > 0.1). The bacterial responses to N fertilization as well as the bacterial and fungal responses to elevated ozone were all phylogenetically conserved, showing universal homogeneous selection (homogeneous environmental conditions leading to more similar community structures). In detail, bacterial Alphaproteobacteria, Actinobacteria, and Chloroflexi, as well as fungal Ascomycota, were increased by elevated ozone, whereas bacterial Gammaproteobacteria, Bacteroidetes, and Elusimicrobia, as well as fungal Glomeromycota, were decreased by elevated ozone (P < 0.05). These ozone-responsive phyla were generally correlated (P < 0.05) with plant biomass, plant carbon (C) uptake, and soil dissolved organic C, demonstrating that elevated ozone affects plant-microbe interactions. Our study highlighted that microbial responses to elevated ozone display a phylogenetic clustering pattern, suggesting that response strategies to elevated ozone stress may be phylogenetically conserved ecological traits. IMPORTANCE The interactions of plant and soil microbial communities support plant growth and health. The increasing tropospheric ozone decreases crop biomass and also alters soil microbial communities, but the ways in which crops and their associated soil microbial communities respond to elevated tropospheric ozone are not clear, and it is also obscure whether the interactions between ozone and the commonly applied N fertilization exist. We showed that the microbial responses to both elevated ozone and N fertilization were phylogenetically conserved. However, the microbial communities that responded to N fertilization and elevated ozone were different, and this was further verified by the lack of an interactive effect between N fertilization and elevated ozone. Given that the global tropospheric ozone concentration will continue to increase in the coming decades, the decrease of specific microbial populations caused by elevated ozone would result in the extinction of certain microbial taxa. This ozone-induced effect will further harm crop production, and awareness is urgently needed.

Revealing microcystin-LR ecotoxicity to earthworm (Eisenia fetida) at the intestinal cell level.

Potential adverse effects of microcystin-LR (MC-LR) on soil invertebrates have not been studied. Here we investigated the mechanism of MC-LR toxicity to earthworm (Eisenia fetida) intestine at the individual level and at the cellular level. The results showed an inverse relationship between the bodyweight and survival rate of earthworms over exposure time- and MC-LR doses in soil. Dose-dependent intestinal lesions and disturbances of enzymatic activities (e.g., cellulase, Na+/K+-ATPase, and AChE) were observed, which resulted in intestinal dysfunction. Excessive reactive oxygen species generation led to DNA damage and lipid peroxidation of intestinal cells. The oxidative damage to DNA prolonged cell cycle arrest at the G2/M-phase transition in mitosis, thus stimulating and accelerating apoptosis in earthworm intestine. MC-LR target earthworm intestine tissue. MC-LR at low concentrations can damage earthworm intestine regardless of exposure routes (oral or contact). High toxicity of MC-LR to earthworms delineates its ecological risks to terrestrial ecosystems.