A metagenomics study of hexabromocyclododecane degradation with a soil microbial community

Stereoisomer-specific bacterial mechanisms for hexabromocyclododecane biotransformation

Hexabromocyclododecane (HBCD), a flame retardant classified as a Persistent Organic Pollutant (POP), undergoes stereoisomer-specific microbial transformation with significant environmental and health implications. However, the underlying mechanisms of this stereoisomer-specific microbial transformation remain poorly understood. In this study, high-purity HBCD chiral isomers were isolated using an optimized high-performance liquid chromatography (HPLC) method and their transformation by Acinetobacter hemolyticum sp. strain HW-2 was investigated through transcriptomic analysis. Within three days, strain HW-2 removed (+) α-, (-) α-, (+) β-, (-) β-, (+) γ-, and (-) γ-HBCD with respective removal efficiencies of 52.38 %, 71.08 %, 71.07 %, 63.34 %, 47.47 %, and 77.05 %. Transcriptomic data revealed stereoisomer-specific processes in HBCD transport, response, and transformation. Strain HW-2 upregulated major facilitator superfamily (MFS) transport genes for HBCD uptake, with distinct genes activated for different diastereoisomers. Compared to γ-HBCD, α- and β-HBCD exerted greater stress on strain HW-2, leading to increased expression of efflux genes and antioxidant-related genes. The transformation of HBCD stereoisomers involved distinct functional enzymes, with only (-) γ-HBCD metabolized via the aromatic compound metabolic pathway. This study elucidates the stereoisomeric-specific transformation mechanisms underlying HBCD transformation by strain HW-2, offering valuable insights for theoretical and practical applications in HBCD remediation.

Understanding arbuscular mycorrhizal fungi's contribution to hexabromocyclododecane metabolism: Pathways and ecological implications in contaminated environments

This study investigates the role of arbuscular mycorrhizal fungi (AMF) in the metabolism of hexabromocyclododecane (HBCD) and its ecological effects in contaminated environments. We focused on the symbiotic relationships between Iris pseudacorus L. and AMF (Rhizophagus irregularis) under HBCD exposure. Our results show that HBCD induces oxidative damage, which hinders plant growth. However, AMF significantly enhance the plant's antioxidant defenses, reducing oxidative damage and supporting better growth of I. pseudacorus. HBCD biodegradation patterns showed β- > γ- > α-HBCD, with AMF playing a key role in stabilizing rhizosphere microbial communities, particularly promoting Proteobacteria and potential bacterial degraders like Aeromonas and Trichococcus, which contributed to HBCD removal. Additionally, AMF appear to upregulate genes such as cypD_E, GST, dehH, dehA, dehM, Em3.8.1.2, and ligB, which are involved in debromination and hydroxylation reactions. This research highlights AMF's potential to enhance the phytoremediation of HBCD, providing valuable insights for environmental remediation strategies.

Enhanced microbial degradation of hexabromocyclododecane in riparian sediments through regulating flooding regimes

Hexabromocyclododecane (HBCD), a persistent halogenated organic pollutant, has been commonly detected in river sediments, especially in riparian zones, but strategies for promoting its microbial degradation remain insufficiently explored. This study hypothesized that regulating the flooding regime of sediments could accelerate microbial degradation of HBCD in riparian zones and evaluated the underlying mechanisms. Results showed that, compared with high-frequency flooding-drying or no alternations, the low-frequency flooding-drying alternation (6 weeks of flooding and 6 weeks of drying, 6F:6D) significantly promoted microbial degradation of HBCD. This may be due to changes in sediment redox potential under the 6F:6D regime, facilitating the sequential reductive debromination and aerobic degradation process of HBCD. The abundances of organohalide-respiring bacteria (Dehalococcoides spp. and Dehalogenimonas spp.) were always high in the 6F:6D regime, irrespective of flooding or drying periods. Furthermore, the complex bacterial co-occurrence patterns, specific ecological clusters, and potential keystone species including the genera Methylibium, Nitrospira, and Dehalococcoides, may play important degradative roles of HBCD in the 6F:6D regime. Overall, microbial degradation of HBCD can be promoted under low-frequency flooding-drying alternation regulated by hydraulic structures, providing an effective and eco-friendly strategy for ecological restoration.

Interpretation of machine learning-based prediction models and functional metagenomic approach to identify critical genes in HBCD degradation

Hexabromocyclododecane (HBCD) poses significant environmental risks, and identifying HBCD-degrading microbes and their enzymatic mechanisms is challenging due to the complexity of microbial interactions and metabolic pathways. This study aimed to identify critical genes involved in HBCD biodegradation through two approaches: functional annotation of metagenomes and the interpretation of machine learning-based prediction models. Our functional analysis revealed a rich metabolic potential in Chiang Chun soil (CCS) metagenomes, particularly in carbohydrate metabolism. Among the machine learning algorithms tested, random forest models outperformed others, especially when trained on datasets reflecting the degradation patterns of species like Dehalococcoides mccartyi and Pseudomonas aeruginosa. These models highlighted enzymes such as EC 1.8.3.2 (thiol oxidase) and EC 4.1.1.43 (phenylpyruvate decarboxylase) as inhibitors of degradation, while EC 2.7.1.83 (pseudouridine kinase) was linked to enhanced degradation. This dual-methodology approach not only deepens our understanding of microbial functions in HBCD degradation but also provides an unbiased view of the microbial and enzymatic interactions involved, offering a more targeted and effective bioremediation strategy.

Unveiling the hydrolase Oph2876 mediated chlorpyrifos degradation mechanism in Pseudomonas nitroreducens and its potential for environmental bioremediation

Chlorpyrifos contamination is a currently on-going issue with significant environmental impacts. As such, rapid and effective techniques that remove chlorpyrifos from the environment are urgently required. Here, a strain of Pseudomonas nitroreducens W-7 exhibited exceptional degradation ability towards both chlorpyrifos and its major metabolite 3,5,6-trichloro-2-pyridinol (TCP). W-7 can effectively reduce the toxicity of chlorpyrifos and TCP towards a variety of sensitive organisms through its superior degradation capacity. W-7 demonstrated efficient soil bioremediation by removing over 50 % of chlorpyrifos (25 mg/kg) from both sterile and non-sterile soils within 5 days, with significantly reduced half-lives. Additionally, 16S rDNA high-throughput sequencing of the soil revealed that the introduction of W-7 had no significant impact on the soil microbial community. A pivotal hydrolase Oph2876 containing conserved motif (HxHxDH) and a bimetallic catalytic center was identified from W-7. Oph2876 was a heat- and alkali-resistant enzyme with low sequence similarity (< 44 %) with other reported organophosphorus hydrolases, with a better substrate affinity for hydrolysis of chlorpyrifos to TCP. The molecular docking and site-directed mutagenesis studies indicated that the amino acid residues Asp235, His214, and His282, which were associated with the conserved sequence "HxHxDH", were crucial for the activity of Oph2876. These findings contribute to a better understanding of the biodegradation mechanism of chlorpyrifos and present useful agents for the development of effective chlorpyrifos bioremediation strategies.

Fulvic Acid Enhances Nitrogen Fixation and Retention in Paddy Soils through Microbial-Coupled Carbon and Nitrogen Cycling

Fulvic acid, the most soluble and active humic substance, is widely used as an agent to remediate contaminated soils and improve soil fertility. However, the influence of fulvic acid (FA), as a microbial carbon source, on carbon and nitrogen cycles in paddy soils remains elusive. Therefore, to investigate it, an incubation experiment was conducted. Gas analyses indicated that the carbon dioxide and methane emissions were enhanced in FA treatment, which increased up to 94.08-fold and 5.06-fold, respectively. 15N-labeling experiments revealed that nitrogen fixation capability was promoted (1.2-fold) to reduce the carbon and nitrogen imbalance due to fulvic acid amendment. Metagenomic analysis further revealed that gene abundances of degradation of lignin-like compounds, gallate degradation, methanogenesis, nitrogen fixation, and urea hydrolysis increased, while the bacterial ammonia oxidation and anaerobic ammonium oxidation decreased, caused by FA application. Metabolic reconstruction of metagenome-assembled genomes revealed that Azospirillaceae, Methanosarcinaceae, and Bathyarchaeota, with higher abundance in FA treatment, were the key microorganisms to maintain the carbon and nitrogen balance. The metabolic pathways of fulvic acid degradation and coupled nitrogen fixation and retention were constructed. Collectively, our results provided novel insights into the theoretical basis of the use of humic substances for reducing nitrogen fertilization and climate change.

Enhancing soil petrochemical contaminant remediation through nutrient addition and exogenous bacterial introduction

Biostimulation (providing favorable environmental conditions for microbial growth) and bioaugmentation (introducing exogenous microorganisms) are effective approaches in the bioremediation of petroleum-contaminated soil. However, uncertainty remains in the effectiveness of these two approaches in practical application. In this study, we constructed mesocosms using petroleum hydrocarbon-contaminated soil. We compared the effects of adding nutrients, introducing exogenous bacterial degraders, and their combination on remediating petroleum contamination in the soil. Adding nutrients more effectively accelerated total petroleum hydrocarbon (TPH) degradation than other treatments in the initial 60 days' incubation. Despite both approaches stimulating bacterial richness, the community turnover caused by nutrient addition was gentler than bacterial degrader introduction. As TPH concentrations decreased, we observed a succession in microbial communities characterized by a decline in copiotrophic, fast-growing bacterial r-strategists with high rRNA operon (rrn) copy numbers. Ecological network analysis indicated that both nutrient addition and bacterial degrader introduction enhanced the complexity and stability of bacterial networks. Compared to the other treatment, the bacterial network with nutrient addition had more keystone species and a higher proportion of negative associations, factors that may enhance microbial community stability. Our study demonstrated that nutrient addition effectively regulates community succession and ecological interaction to accelerate the soil TPH degradation.

The unexpected effect of the compound microbial agent NP-M2 on microbial community dynamics in a nonylphenol-contaminated soil: the self-stability of soil ecosystem

Background

Nonylphenol (NP) is widely recognized as a crucial environmental endocrine-disrupting chemical and persistent toxic substance. The remediation of NP-contaminated sites primarily relies on biological degradation. Compound microbial products, as opposed to pure strains, possess a greater variety of metabolic pathways and can thrive in a wider range of environmental conditions. This characteristic is believed to facilitate the synergistic degradation of pollutants. Limited research has been conducted to thoroughly examine the potential compatibility of compound microbial agents with indigenous microflora, their ability to function effectively in practical environments, their capacity to enhance the dissipation of NP, and their potential to improve soil physicochemical and biological characteristics.

Methods

In order to efficiently eliminate NP in contaminated soil in an eco-friendly manner, a simulation study was conducted to investigate the impact of bioaugmentation using the functional compound microbial agent NP-M2 at varying concentrations (50 and 200 mg/L) on the dynamics of the soil microbial community. The treatments were set as follows: sterilized soil with 50 mg/kg NP (CK50) or 200 mg/kg NP (CK200); non-sterilized soil with 50 mg/kg NP (TU50) or 200 mg/kg NP (TU200); non-sterilized soil with the compound microbial agent NP-M2 at 50 mg/kg NP (J50) or 200 mg/kg NP (J200). Full-length 16S rRNA analysis was performed using the PacBio Sequel II platform.

Results

Both the indigenous microbes (TU50 and TU200 treatments) and the application of NP-M2 (J50 and J200 treatments) exhibited rapid NP removal, with removal rates ranging from 93% to 99%. The application of NP-M2 further accelerated the degradation rate of NP for a subtle lag period. Although the different treatments had minimal impacts on the soil bacterial α-diversity, they significantly altered the β-diversity and composition of the bacterial community. The dominant phyla were Proteobacteria (35.54%-44.14%), Acidobacteria (13.55%-17.07%), Planctomycetes (10.78%-11.42%), Bacteroidetes (5.60%-10.74%), and Actinobacteria (6.44%-8.68%). The core species were Luteitalea_pratensis, Pyrinomonas_methylaliphatogenes, Fimbriiglobus_ruber, Longimicrobium_terrae, and Massilia_sp003590855. The bacterial community structure and taxon distribution in polluted soils were significantly influenced by the activities of soil catalase, sucrase, and polyphenol oxidase, which were identified as the major environmental factors. Notably, the concentration of NP and, to a lesser extent, the compound microbial agent NP-M2 were found to cause major shifts in the bacterial community. This study highlights the importance of conducting bioremediation experiments in conjunction with microbiome assessment to better understand the impact of bioaugmentation/biostimulation on the potential functions of complex microbial communities present in contaminated soils, which is essential for bioremediation success.

Insights into the influence of polystyrene microplastics on the bio-degradation behavior of tetrabromobisphenol A in soil

Soil contamination by emerging pollutants tetrabromobisphenol A (TBBPA) and microplastics has become a global environmental issue in recent years. However, little is known about the effect of microplastics on degradation of TBBPA in soil, especially aged microplastics. In this study, the effect of aged polystyrene (PS) microplastics on the degradation of TBBPA in soil and the mechanisms were investigated. The results suggested that the aged microplastics exhibited a stronger inhibitory effect on the degradation of TBBPA in soil than the pristine microplastics, and the degradation efficiency of TBBPA decreased by 21.57% at the aged microplastic content of 1%. This might be related to the higher TBBPA adsorption capacity of aged microplastics compared to pristine microplastics. Aged microplastics strongly altered TBBPA-contaminated soil properties, reduced oxidoreductase activity and affected microbial community composition. The decrease in soil oxidoreductase activity and relative abundance of functional microorganisms (e.g., Bacillus, Pseudarthrobacter and Sphingomonas) caused by aged microplastics interfered with metabolic pathways of TBBPA. This study indicated the importance the risk assessment and soil remediation for TBBPA-contaminated soil with aged microplastics.

Bromine contamination and risk management in terrestrial and aquatic ecosystems

Bromine (Br) is widely distributed through the lithosphere and hydrosphere, and its chemistry in the environment is affected by natural processes and anthropogenic activities. While the chemistry of Br in the atmosphere has been comprehensively explored, there has never been an overview of the chemistry of Br in soil and aquatic systems. This review synthesizes current knowledge on the sources, geochemistry, health and environmental threats, remediation approaches, and regulatory guidelines pertaining to Br pollution in terrestrial and aquatic environments. Volcanic eruptions, geothermal streams, and seawater are the major natural sources of Br. In soils and sediments, Br undergoes natural cycling between organic and inorganic forms, with bromination reactions occurring both abiotically and through microbial activity. For organisms, Br is a non-essential element; it is passively taken up by plant roots in the form of the Br- anion. Elevated Br- levels can limit plant growth on coastal soils of arid and semi-arid environments. Br is used in the chemical industry to manufacture pesticides, flame retardants, pharmaceuticals, and other products. Anthropogenic sources of organobromine contaminants in the environment are primarily wastewater treatment, fumigants, and flame retardants. When aqueous Br- reacts with oxidants in water treatment plants, it can generate brominated disinfection by-products (DBPs), and exposure to DBPs is linked to adverse human health effects including increased cancer risk. Br- can be removed from aquatic systems using adsorbents, and amelioration of soils containing excess Br- can be achieved by leaching, adding various amendments, or phytoremediation. Developing cost-effective methods for Br- removal from wastewater would help address the problem of toxic brominated DBPs. Other anthropogenic organobromines, such as polybrominated diphenyl ether (PBDE) flame retardants, are persistent, toxic, and bioaccumulative, posing a challenge in environmental remediation. Future research directives for managing Br pollution sustainably in various environmental settings are suggested here.

Biotransformation of HBCDs by the microbial communities enriched from mangrove sediments

1,2,5,6,9,10-Hexabromocyclododecanes (HBCDs) are a sort of persistent organic pollutants (POPs). This research investigated 12 microbial communities enriched from sediments of four mangroves in China to transform HBCDs. Six microbial communities gained high transformation rates (27.5-97.7%) after 12 generations of serial transfer. Bacteria were the main contributors to transform HBCDs rather than fungi. Analyses on the bacterial compositions and binning genomes showed that Alcanivorax (55.246-84.942%) harboring haloalkane dehalogenase genes dadAH and dadBH dominated the microbial communities with high transformation rates. Moreover, expressions of dadAH and dadBH in the microbial communities and Alcanivorax isolate could be induced by HBCDs. Further, it was found that purified proteins DadAH and DadBH showed high conversion rates on HBCDs in 36 h (91.9 ± 7.4 and 101.0 ± 1.8%, respectively). The engineered Escherichia coli BL21 strains harbored two genes could convert 5.7 ± 0.4 and 35.1 ± 0.1% HBCDs, respectively, lower than their cell-free crude extracts (61.2 ± 5.2 and 56.5 ± 8.7%, respectively). The diastereoisomer-specific transforming trend by both microbial communities and enzymes were γ- > α- > β-HBCD, differed from α- > β- > γ-HBCD by the Alcanivorax isolate. The identified transformation products indicated that HBCDs were dehalogenated via HBr elimination (dehydrobromination), hydrolytic and reductive debromination pathways in the enriched cultures. Two enzymes converted HBCDs via hydrolytic debromination. The present research provided theoretical bases for the biotransformation of HBCDs by microbial community and the bioremediation of HBCDs contamination in the environment.

Biotransformation of 6:2 fluorotelomer sulfonate and microbial community dynamics in water-saturated one-dimensional flow-through columns

Nearly all per- and polyfluoroalkyl substances (PFAS) biotransformation studies reported to date have been limited to laboratory-scale batch reactors. The fate and transport of PFAS in systems that more closely represent field conditions, i.e., in saturated porous media under flowing conditions, remain largely unexplored. This study investigated the biotransformation of 6:2 fluorotelomer sulfonate (6:2 FTS), a representative PFAS of widespread environmental occurrence, in one-dimensional water-saturated flow-through columns packed with soil obtained from a PFAS-contaminated site. The 305-day column experiments demonstrated that 6:2 FTS biotransformation was rate-limited, where a decrease in pore-water velocity from 3.7 to 2.4 cm/day, resulted in a 21.7-26.1 % decrease in effluent concentrations of 6:2 FTS and higher yields (1.0-1.4 mol% vs. 0.3 mol%) of late-stage biotransformation products (C4C7 perfluoroalkyl carboxylates). Flow interruptions (2 and 7 days) were found to enhance 6:2 FTS biotransformation during the 6-7 pore volumes following flow resumption. Model-fitted 6:2 FTS column biotransformation rates (0.039-0.041 cmw3/gs/d) were ∼3.5 times smaller than those observed in microcosms (0.137 cmw3/gs/d). Additionally, during column experiments, planktonic microbial communities remained relatively stable, whereas the composition of the attached microbial communities shifted along the flow path, which may have been attributed to oxygen availability and the toxicity of 6:2 FTS and associated biotransformation products. Genus Pseudomonas dominated in planktonic microbial communities, while in the attached microbial communities, Rhodococcus decreased and Pelotomaculum increased along the flow path, suggesting their potential involvement in early- and late-stage 6:2 FTS biotransformation, respectively. Overall, this study highlights the importance of incorporating realistic environmental conditions into experimental systems to obtain a more representative assessment of in-situ PFAS biotransformation.

Screening, cloning, immobilization and application prospects of a novel β-glucosidase from the soil metagenome

The soil environment for straw return is a rich and valuable library containing many microorganisms and proteins. In this study, we aimed to screen a high-quality β-glucosidase (BGL) from the soil metagenomic library and to overcome the limitation of the low extraction rate of resveratrol in Polygonum cuspidatum. This includes the construction of a soil metagenomic library, screening of BGL, bioinformatics analysis, cloning, expression, immobilization, enzymatic property analysis, and application for the transformation of polydatin. The results showed that the soil metagenomic library of straw return was successfully constructed, and a novel BGL was screened. The identified 1356 bp long BGL belonged to the glycoside hydrolase 1 (GH1) family and was named Bgl1356. After successful cloning and expression of Bgl1356, it was immobilized using chitosan. The optimum temperature of immobilized Bgl1356 was 50 °C, and the pH was 5. It exhibited good tolerance for various metal ions (CO2+, Ni2+, Cu2+, Mn2+, Na2+, Ca2+, and Ag+) and organic solvents (DMSO, Triton-X-10, and ethanol). Enzymatic kinetics assays showed that Bgl1356 had good affinity for the substrate, and the specific enzyme activity was 234.03 U/mg. The conversion rate of polydatin by immobilized Bgl1356 was 95.70 ± 1.08%, facilitating the production of high amounts of resveratrol. Thus, this paper reports a novel temperature-, organic solvent-, and metal ion-tolerant BGL that has good application prospects in the pharmaceutical industry.

Integration of ammonium assimilation with denitrifying phosphorus removal for efficient nutrient management in wastewater treatment

Nutrient removal from sewage is transitioning to nutrient recovery. However, biological treatment technologies to remove and recover nutrients from domestic sewage are still under investigation. This study delved into the integration of ammonium assimilation with denitrifying phosphorus removal (DPR) as a method for efficient nutrient management in sewage treatment. Results indicated this approach eliminated over 80 % of the nitrogen in the influent, simultaneously recovering over 60 % of the nitrogen as the activated sludge through ammonia assimilation, and glycerol facilitated this process. The nitrification/denitrifying phosphorus removal ensured the stability of both nitrogen and phosphorus removal. The phosphorus removal rate exceeded 96 %, and the DPR rate reached over 90 %. Network analysis highlighted a stable community structure with Proteobacteria and Bacteroidota driving ammonium assimilation. The synergistic effect of fermentation bacteria, denitrifying glycogen-accumulating organisms, and denitrifying phosphorus-accumulating organisms contributed to the stability of nitrogen and phosphorus removal. This approach offers a promising method for sustainable nutrient management in sewage treatment.

Effects of hexabromocyclododecane and polyethylene microplastics on soil bacterial communities

Hexabromocyclododecane (HBCD) and polyethylene (PE) microplastic are ubiquitous pollutants, and knowledge about the effects of HBCD and PE pollution on soil bacterial communities remains obscure. In this study, the effects of different HBCD and PE concentrations and combined HBCD and PE exposure on the diversity, composition, and function of agricultural soil bacterial communities over 4 months were systematically examined for the first time. Generally, soil bacterial communities were influenced in both the 1-month and 4-month scenarios through HBCD and PE separately as well as combined exposure. After 4 months of exposure, PE and combined exposure significantly affected soil bacterial alpha diversity, however, low concentration of HBCD showed no apparent influence. 1-month and 4-month HBCD, PE, and combined exposure significantly influenced bacterial beta diversity. Compared with 1 month of exposure, HBCD, PE, and combined exposure demonstrated remarkable influences on soil bacteria after 4 months of exposure, especially on Nitrospirae, Elusimicrobia, Rokubacteria at the phylum level, and on MND1, Ruminiclostridium, Lysobacter, Anaeromyxobacter, Alistipes, WCHB1 at the genus level. The bacterial function analysis indicated that amino acid metabolism, carbohydrate metabolism, and membrane transport were the three predominant enriched bacterial functions after 1-month and 4-month HBCD and PE exposure. This research provides a comprehensive grasp of the effects of HBCD and PE pollution on soil microbial communities, which could have a beneficial impact on future soil pollution control.

Vertical and seasonal dynamics of bacterial pathogenic communities at an aged organic contaminated site: Insights into microbial diversity, composition, interactions, and assembly processes

Under the background of the Coronavirus Disease 2019 (COVID-19) pandemic, research on pathogens deserves greater attention in the natural environment, especially in the widely distributed contaminated sites with complicated and severe organic pollution. In this study, the community composition and assembly of soil pathogens identified by the newly-developed 16S-based pipeline of multiple bacterial pathogen detection (MBPD) have been investigated on spatiotemporal scales in the selected organic polluted site. We demonstrated that the richness and diversity of the pathogenic communities were primarily controlled by soil depth, while the structure and composition of pathogenic communities varied pronouncedly with seasonal changes, which were driven by the alterations in both physiochemical parameters and organic contaminants over time. Network analysis revealed that the overwhelmingly positive interactions, identified multiple keystone species, and a well-organized modular structure maintained the stability and functionality of the pathogenic communities under environmental pressures. Additionally, the null-model analysis showed that deterministic processes dominated the pathogenic community assembly across soil profiles. In three seasons, stochasticity-dominated processes in spring and summer changed into determinism-dominated processes in winter. These findings extend our knowledge of the response of the bacterial pathogenic community to environmental disruptions brought on by organic contaminated sites.

The effects of long-term hexabromocyclododecanes contamination on microbial communities in the microcosms

The adaptation of microbial community to the long-term contamination of hexabromocyclododecanes (HBCDs) has not been well studied. Our previous study found that the HBCDs contamination in the microcosms constructed of sediments from two different mangrove forests in 8 months resulted in serious acidification (pH2-3). This study reanalyzed previous sequencing data and compared them with data after 20 months to investigate the adaptive properties of microbial communities in the stress of HBCDs and acidification. It hypothesized that the reassembly was based on the fitness of taxa. The results indicated that eukaryotes and fungi might have better adaptive capacity to these deteriorated habitats. Eukaryotic taxa Eufallia and Syncystis, and fungal taxa Wickerhamomyces were only detected after 20 months of contamination. Moreover, eukaryotic taxa Caloneis and Nitzschia, and fungal taxa Talaromyces were dominant in most of microbial communities (14.467-95.941%). The functional compositions were sediment-dependent and more divergent than community reassemblies. Network and co-occurrence analysis suggested that acidophiles such as Acidisoma and Acidiphilium were gaining more positive relations in the long-term stress. The acidophilic taxa and genes involved in resistance to the acidification and toxicity of HBCDs were enriched, for example, bacteria Acidisoma and Acidiphilium, archaea Thermogymnomonas, and eukaryotes Nitzschia, and genes kdpC, odc1, polA, gst, and sod-2. These genes involved in oxidative stress response, energy metabolism, DNA damage repair, potassium transportation, and decarboxylation. It suggested that the microbial communities might cope with the stress from HBCDs and acidification via multiple pathways. The present research shed light on the evolution of microbial communities under the long-term stress of HBCDs contamination and acidification.

Acid rain reduces plant-photosynthesized carbon sequestration and soil microbial network complexity

Acid rain threatens the structure and function of terrestrial ecosystems; however, the mechanisms by which acid rain affects the photosynthesized carbon (C) fluxes and soil microbial communities are far less understood, thus impeding accurate projections of regional C flux in the plant-soil-atmosphere system. In this study, we performed an isotopic ¹³C labeling experiment to trace C footprints in a maize-soil system under acid rain pollution (pH 4.5 and 3.0; SO₄^2-/NO₃^-= 2:1). Our results showed that acid rain exerted a negligible effect on total plant biomass as well as shoot biomass. Acid rain of pH 3.0 inhibited plant ¹³C assimilation and the flow of fixed ¹³C to the soil. Acid rain decreased soil total C and organic nitrogen (N) but increased inorganic N (i.e., nitrate-N) content. The acid rain of pH 3.0 enhanced soil bulk density, led to soil acidification, and promoted soil microbial diversity. However, acid rain reduced the connectivity and complexity of soil microbial network. Soil ¹³C content was mainly regulated by soil pH, ammonium-N, and root biomass. Our findings demonstrated that acid rain reduces photosynthesized C sequestration of maize-soil system and soil microbial taxa interactions.

Unraveling consequences of the co-exposure of polyethylene microplastics and acid rain on plant-microbe-soil system

Emerging microplastics (MPs) pollution and continuing acid rain (AR) co-exist in terrestrial ecosystems, and are considered as threats to ecosystems health. However, few data are available on MPs-AR interactions in plant-microbe-soil systems. Here, a microcosm experiment was manipulated to elucidate the co-exposure of polyethylene MPs (PE MPs; 1%, 5% and 10%) and AR (pH 4.0) on soil-lettuce system, in which the properties of soil and lettuce, and their links were explored. We found that 10% PE MPs increased soil CO₂ emission and its temperature sensitivity (Q₁₀) in combination with AR, while 1% PE MPs reduced soil CO₂ emission irrespective of AR. PE MPs addition did not influence lettuce production (total biomass) though its photosynthesis was affected. PE MPs exerted negative impact on soil water availability. PE MPs treatments increased NH₄⁺-N content of soil without AR, and dissolved organic carbon content of soil sprayed with AR. 10% PE MPs combined with AR reduced soil microbial biomass, while soil microbial community diversity was not affected by PE MPs or AR. Interestingly, 10% PE MPs addition altered soil microbial community structure, and promoted the complexity and connectivity of soil microbial networks. 5% and 10% PE MPs addition decreased soil urease activity under AR, but this was not the case without AR. These findings highlight the critical role of AR in regulating PE MPs impacts on plant-microbe-soil ecosystems, and the necessity to incorporate other environmental factors when evaluating the actual impacts or risks of MPs pollution in terrestrial ecosystems.