The mechanisms of pH regulation on promoting volatile fatty acids production from kitchen waste.

The anaerobic acid production experiments were conducted with the pretreated kitchen waste under pH adjustment. The results showed that pH 8 was considered to be the most suitable condition for acid production, especially for the formation of acetic acid and propionic acid. The average value of total volatile fatty acid at pH 8 was 8814 mg COD/L, 1.5 times of that under blank condition. The average yield of acetic acid and propionic acid was 3302 mg COD/L and 2891 mg COD/L, respectively. The activities of key functional enzymes such as phosphotransacetylase, acetokinase, oxaloacetate transcarboxylase and succinyl-coA transferase were all enhanced. To further explore the regulatory mechanisms within the system, the distribution of microorganisms at different levels in the fermentation system was obtained by microbial sequencing, results indicating that the relative abundances of Clostridiales, Bacteroidales, Chloroflexi, Clostridium, Bacteroidetes and Propionibacteriales, which were great contributors for the hydrolysis and acidification, increased rapidly at pH 8 compared with the blank group. Besides, the proportion of genes encoding key enzymes was generally increased, which further verified the mechanism of hydrolytic acidification and acetic acid production of organic matter under pH regulation.

Bacterial community composition and function vary with farmland type and soil depth around a mining area.

Heavy metal pollution can have adverse impacts on microorganisms, plants and even human health. To date, the impact of heavy metals on bacteria in farmland has yielded poor attention, and there is a paucity of knowledge on the impact of land type on bacteria in mining area with heavy metal pollution. Around a metal-contaminated mining area, two soil depths in three types of farmlands were selected to explore the composition and function of bacteria and their correlations with the types and contents of heavy metals. The compositions and functions of bacterial communities at the three different agricultural sites were disparate to a certain extent. Some metabolic functions of bacterial community in the paddy field were up-regulated compared with those at other site. These results observed around mining area were different from those previously reported in conventional farmlands. In addition, bacterial community composition in the top soils was relatively complex, while in the deep soils it became more unitary and extracellular functional genes got enriched. Meanwhile, heavy metal pollution may stimulate the enrichment of certain bacteria to protect plants from damage. This finding may aid in understanding the indirect effect of metal contamination on plants and thus putting forward feasible strategies for the remediation of metal-contaminated sites. MAIN FINDINGS OF THE WORK: This was the first study to comprehensively explore the influence of heavy metal pollution on the soil bacterial communities and metabolic potentials in different agricultural land types and soil depths around a mining area.

Metagenomic insights into microbial metabolic mechanisms of a combined solid-phase denitrification and anammox process for nitrogen removal in mainstream wastewater treatment.

To overcome the significant challenges associated with nitrite supply and nitrate residues in mainstream anaerobic ammonium oxidation (anammox)-based processes, this study developed a combined solid-phase denitrification (SPD) and anammox process for low-strength nitrogen removal without the addition of nitrite. The SPD step was performed in a packed-bed reactor containing poly-3-hydroxybutyrate-co-3-hyroxyvelate (PHBV) prior to employing the anammox granular sludge reactor in the continuous-flow mode. The removal efficiency of total inorganic nitrogen reached 95.7 ± 1.2% under a nitrogen loading rate of 0.18 ± 0.01 kg N·m3·d-1, and it required 1.02 mol of nitrate to remove 1 mol of ammonium nitrogen. The PHBV particles not only served as biofilm carriers for the symbiosis of hydrolytic bacteria (HB) and denitrifying bacteria (DB), but also carbon sources that facilitated the coupling of partial denitrification and anammox in the granules. Metagenomic sequencing analysis indicated that Burkholderiales was the most abundant HB genus in SPD. The metabolic correlations between DB (Betaproteobacteria, Rhodocyclaceae, and Anaerolineae) and anammox bacteria (Candidatus Brocadiac and Kuenenia) in the granules were confirmed through microbial co-occurrence networks analysis and functional gene annotations. Additionally, the genes encoding nitrate reductase (Nap) and nitrite reductase (Nir) in DB primarily facilitated nitrate reduction, thereby supplying nitric oxide to anammox bacteria for subsequent nitrogen removal with hydrazine synthase (Hzs) and hydrazine dehydrogenase (Hdh). The findings provide insights into microbial metabolism within combined SPD and anammox processes, thus advancing the development of mainstream anammox-based processes in engineering applications.

Unveiling microplastic's role in nitrogen cycling: metagenomic insights from estuarine sediment microcosms.

Marine microplastics (MPs) pollution, with rivers as a major source, leads to MPs accumulation in estuarine sediments, which are also nitrogen cycling hotspots. However, the impact of MPs on nitrogen cycling in estuarine sediments has rarely been documented. In this study, we conducted microcosm experiment to investigate the effects of commonly encountered polyethylene (PE) and polystyrene (PS) MPs, with two MPs concentrations (0.3% and 3% wet sediment weight) based on environmental concentration considerations and dose-response effects, on sediment dissolved oxygen (DO) diffusion capacity and microbial communities using microelectrode system and metagenomic analysis respectively. The results indicated that high concentrations of PE-MPs inhibited DO diffusion during the mid-phase of the experiment, an effect that dissipated in the later stages. Metagenomic analysis revealed that MP treatments reduced the relative abundance of dominant microbial colonies in the sediments. The PCoA results demonstrated that MPs altered the microbial community structure, particularly evident under high concentration PE-MPs treatments. Functional analysis related to the nitrogen cycle suggested that PS-MPs promoted the nitrification, denitrification, and DNRA processes, but inhibited the ANRA process, while PE-MPs had an inhibitory effect on the nitrate reduction process and the ANRA process. Additionally, the high concentration of PE-MPs treatment significantly stimulated the abundance of genus (Bacillus) by 34.1% and genes (lip, pnbA) by 100-187.5% associated with plastic degradation, respectively. Overall, in terms of microbial community structure and the abundance of nitrogen cycling functional genes, PE- and PS- MPs exhibit both similarities and differences in their impact on nitrogen cycling. Our findings highlight the complexity of MP effects on nitrogen cycling in estuarine sediments and high concentrations of PE-MP stimulated plastic-degrading genus and genes.

[Identification and functional characterization of candidate genes involved in biosynthesis of ginsenoside Rg_1].

Panax ginseng is a perennial herb with the main active compounds of ginsenosides. Among the reported ginsenosides, ginsenoside Rg_1 not only has a wide range of medicinal functions and abundant content but also is one of the major ginsenoside for the quality evaluation of this herb in the Chinese Pharmacopoeia. The main biosynthesis pathway of ginsenoside Rg_1 in P. ginseng has been clarified, which lays a foundation for the comprehensive and in-depth analysis of the biosynthesis and regulatory mechanism of ginseno-side Rg_1. However, the biosynthesis of ginsenoside Rg_1 is associated with other complex processes involving a variety of regulatory genes and catalyzing enzyme genes, which remain to be studied comprehensively. With the transcriptome data of 344 root samples from 4-year-old P. ginseng plants and their corresponding ginsenoside Rg_1 content obtained in the previous study, this study screened out 217 differentially expressed genes(DEGs) with Rg_1 content changes by DEseq2 analysis in R language. Furthermore, the weighted gene co-expression network analysis(WGCNA) revealed 40 hub genes among the DEGs.Pearsoncorrelation analysis was further perforned to yield 20 candidate genes significantly correlated with ginsenoside Rg_1 content, and these genes were annotated to multiple metabolic processes including primary metabolism and secondary metabolism. Finally, the treatment of P. ginseng adventitious roots with methyl jasmonate indicated that 16 of these genes promoted the biosynthesis of ginsenoside Rg_1 in response to methyl jasmonate induction. Finally, one of the 16 genes was randomly selected to verify the function of the gene by genetic transformation and qRT-PCR and to confirm the rationality of the methodology of this study. The above results lay a foundation for studying the mechanism for regulation on the synthesis of ginsenoside Rg_1 and provide genetic resources for the industrial production of ginsenoside Rg_1.

Microbial community succession and responses to internal environmental drivers throughout the operation of constructed wetlands.

Constructed wetlands (CWs) have been widely used to ensure effective domestic wastewater treatment. Microorganisms-derived CWs have received extensive attention as they play a crucial role. However, research on the succession patterns of microbial communities and the influencing mechanisms of internal environmental factors throughout entire CW operations remains limited. In this context, three parallel-operated CWs were established in this study to assess the microbial communities and their influencing environmental factors at different substrate depths throughout the operation process using 16S rRNA gene high-throughput sequencing and metagenomic sequencing. The results showed gradual reproduction and accumulation of the microbial communities throughout the CW operation. Although gradual increases in the richness and diversity of the microbial communities were found, there were decreases in the functional expression of the dominant microbial species. The excessive accumulation of microorganisms will decrease the oxidation-reduction potential (ORP) within CWs and attenuate their influence on effluent. Dissolved oxygen (DO) was the major factor influencing the microbial community succession over the CW operation. The main identified functional bacterial genera responsible for the ammonium oxidation, nitrification, and denitrification processes in the CWs were Nitrosospira, Nitrobacter, Nitrospira, Rhodanobacter, and Nakamurella. The narG gene was identified as a key functional gene linking various components of nitrogen cycling, while pH, electrical conductivity (EC), and ORP were the major environmental factors affecting the metabolism characteristics of nitrogen functional microorganisms. This study provides a theoretical basis for the effective regulation of related microbial communities to achieve long-term, efficient, and stable CW operations.

Effect of nitrogen addition on soil net nitrogen mineralization in topsoil and subsoil regulated by soil microbial properties and mineral protection: Evidence from a long-term grassland experiment.

Soil net nitrogen mineralization (Nmin), a microbial-mediated conversion of organic to inorganic N, is critical for grassland productivity and biogeochemical cycling. Enhanced atmospheric N deposition has been shown to substantially increase both plant and soil N content, leading to a major change in Nmin. However, the mechanisms underlying microbial properties, particularly microbial functional genes, which drive the response of Nmin to elevated N deposition are still being discussed. Besides, it is still uncertain whether the relative importance of plant carbon (C) input, microbial properties, and mineral protection in regulating Nmin under continuous N addition would vary with the soil depth. Here, based on a 13-year multi-level field N addition experiment conducted in a typical grassland on the Loess Plateau, we elucidated how N-induced changes in plant C input, soil physicochemical properties, mineral properties, soil microbial community, and the soil Nmin rate (Rmin)-related functional genes drove the responses of Rmin to N addition in the topsoil and subsoil. The results showed that Rmin increased significantly in both topsoil and subsoil with increasing rates of N addition. Such a response was mainly dominated by the rate of soil nitrification. Structural equation modeling (SEM) revealed that a combination of microbial properties (functional genes and diversity) and mineral properties regulated the response of Rmin to N addition at both soil depths, thus leading to changes in the soil N availability. More importantly, the regulatory impacts of microbial and mineral properties on Rmin were depth-dependent: the influences of microbial properties weakened with soil depth, whereas the effects of mineral protection enhanced with soil depth. Collectively, these results highlight the need to incorporate the effects of differential microbial and mineral properties on Rmin at different soil depths into the Earth system models to better predict soil N cycling under further scenarios of N deposition.

Response of soil microbial community structure and function to the sewage leakage: A case study of a 25-year-old cesspool.

Providing many millions of rural households with decentralized sanitation facilities remains challenging. In undeveloped areas, cesspools have still been widely used due to technologically simple and low-cost. However, the influence of cesspools on the surrounding soil remains unclear. In this study, we investigated the influence of a 25-year-old household cesspool on soil physicochemical factors, microbial community composition and function, pathogens and antibiotic resistance genes (ARGs). Soil at the depth around the sewage liquid level (D70) was mostly disturbed where TOC, NO3-N and TP was increased to 16.8 g/kg, 18.2 mg/kg and 1.02 mg/kg respectively. Correspondingly, the element cycling genes of carbon fixation, methanotrophy, nitrogen fixation, ammonia oxidation, and nitrate reduction etc., were increased at D70. Notably, human derived pathogens such as Enterobacter, Salmonella, Pseudomonas aeruginosa, Klebsiella pneumoniae, Prevotella, and Vibrio were highly enriched by 5-10 folders in D70, indicating the potential health risk to human. Mantel tests suggested that EC, TP, pH, NH3-N and particularly NO3-N are important factors that influence the microbial community and element cycling genes in cesspool-affected soil. Overall, this study revealed the impact of household cesspool leakage on the surrounding soil and provided information for the selection and construction of basic sanitation facilities in poor regions.

Evidence of nitrogen inputs affecting soil nitrogen purification by mediating root exudates of salt marsh plants.

Salt marsh has an important 'purification' role in coastal ecosystems by removing excess nitrogen that could otherwise harm aquatic life and reduce water quality. Recent studies suggest that salt marsh root exudates might be the 'control centre' for nitrogen transformation, but empirical evidence is lacking. Here we sought to estimate the direction and magnitude of nitrogen purification by salt marsh root exudates and gain a mechanistic understanding of the biogeochemical transformation pathway(s). To achieve this, we used a laboratory incubation to quantify both the root exudates and soil nitrogen purification rates, in addition to the enzyme activities and functional genes under Phragmites australis populations with different nitrogen forms addition (NO3-, NH4+ and urea). We found that NO3- and urea addition significantly stimulate P. australis root exudation of total acids, amino acids, total sugars and total organic carbon, while NH4+ addition only significantly increased total acids, amino acids and total phenol exudation. High total sugars, amino acids and total organic carbon concentrations enlarged nitrogen purification potential by stimulating the nitrogen purifying bacterial activities (including enzyme activities and related genes expression). Potential denitrification rates were not significantly elevated under NH4+ addition in comparison to NO3- and urea addition, which should be ascribed to total phenol self-toxicity and selective inhibition. Further, urea addition stimulated urease and protease activities with providing more NH4+ and NO2- substrates for elevated anaerobic ammonium oxidation rates among the nitrogen addition treatments. Overall, this study revealed that exogenous nitrogen could increase the nitrogen purification-associated bacterial activity through accelerating the root exudate release, which could stimulate the activity of nitrogen transformation, and then improve the nitrogen removal capacity in salt marsh.

Metagenomic insights into nitrogen cycling functional gene responses to nitrogen fixation and transfer in maize-peanut intercropping.

The fixation and transfer of biological nitrogen from peanuts to maize in maize-peanut intercropping systems play a pivotal role in maintaining the soil nutrient balance. However, the mechanisms through which root interactions regulate biological nitrogen fixation and transfer remain unclear. This study employed a 15N isotope labelling method to quantify nitrogen fixation and transfer from peanuts to maize, concurrently elucidating key microorganisms and genera in the nitrogen cycle through metagenomic sequencing. The results revealed that biological nitrogen fixation in peanut was 50 mg and transfer to maize was 230 mg when the roots interacted. Moreover, root interactions significantly increased nitrogen content and the activities of protease, dehydrogenase (DHO) and nitrate reductase in the rhizosphere soil. Metagenomic analyses and structural equation modelling indicated that nrfC and nirA genes played important roles in regulating nitrogen fixation and transfer. Bradyrhizobium was affected by soil nitrogen content and DHO, indirectly influencing the efficiency of nitrogen fixation and transfer. Overall, our study identified key bacterial genera and genes associated with nitrogen fixation and transfer, thus advancing our understanding of interspecific interactions and highlighting the pivotal role of soil microorganisms and functional genes in maintaining soil ecosystem stability from a molecular ecological perspective.

Metagenomic clustering links specific metabolic functions to globally relevant ecosystems.

Metagenomic sequencing has advanced our understanding of biogeochemical processes by providing an unprecedented view into the microbial composition of different ecosystems. While the amount of metagenomic data has grown rapidly, simple-to-use methods to analyze and compare across studies have lagged behind. Thus, tools expressing the metabolic traits of a community are needed to broaden the utility of existing data. Gene abundance profiles are a relatively low-dimensional embedding of a metagenome's functional potential and are, thus, tractable for comparison across many samples. Here, we compare the abundance of KEGG Ortholog Groups (KOs) from 6,539 metagenomes from the Joint Genome Institute's Integrated Microbial Genomes and Metagenomes (JGI IMG/M) database. We find that samples cluster into terrestrial, aquatic, and anaerobic ecosystems with marker KOs reflecting adaptations to these environments. For instance, functional clusters were differentiated by the metabolism of antibiotics, photosynthesis, methanogenesis, and surprisingly GC content. Using this functional gene approach, we reveal the broad-scale patterns shaping microbial communities and demonstrate the utility of ortholog abundance profiles for representing a rapidly expanding body of metagenomic data. IMPORTANCE: Metagenomics, or the sequencing of DNA from complex microbiomes, provides a view into the microbial composition of different environments. Metagenome databases were created to compile sequencing data across studies, but it remains challenging to compare and gain insight from these large data sets. Consequently, there is a need to develop accessible approaches to extract knowledge across metagenomes. The abundance of different orthologs (i.e., genes that perform a similar function across species) provides a simplified representation of a metagenome's metabolic potential that can easily be compared with others. In this study, we cluster the ortholog abundance profiles of thousands of metagenomes from diverse environments and uncover the traits that distinguish them. This work provides a simple to use framework for functional comparison and advances our understanding of how the environment shapes microbial communities.

Phosphorus immobilization in sulfide-ferrous oxidation process driven by nitrate reduction during black-odorous sediment remediation.

During remediation of black-odorous sediment, the pathways of phosphorus immobilization require clarification alongside the oxidation of sulfide and ferrous. This study separated the oxidation stages of sulfide and ferrous through controlled sodium nitrate dosing ratios and methods, and analyzed the changes in phosphorus species and immobilization effects throughout these processes. Results showed that iron-bound phosphorus was the primary contributor to the phosphorus immobilization capacity of the sediment, with the increase ranging from 15 % to 56 % and affected the transformation between phosphorus sources or sinks across varying oxidation states. Additionally, the increase in abundance of phosphorus uptake and transport genes and of denitrifying phosphorus accumulation genes in sediment after ferrous oxidation (1 %-18 % and 87 %-164 %, respectively) indicated the potential for biological phosphorus immobilization. These results demonstrated that higher degrees of sediment oxidation correlate with stronger phosphorus immobilization capacities, providing theoretical bases for phosphorus immobilization during the restoration of black-odorous water bodies.

Integrated Multi-Omics Analysis to Reveal the Molecular Mechanisms of Inflorescence Elongation in Medicago sativa.

The morphological architecture of inflorescence influences seed production. The regulatory mechanisms underlying alfalfa (Medicago sativa) inflorescence elongation remain unclear. Therefore, in this study, we conducted a comparative analysis of the transcriptome, proteome, and metabolome of two extreme materials at three developmental stages to explore the mechanisms underlying inflorescence elongation in alfalfa. We observed the developmental processes of long and short inflorescences and found that the elongation capacity of alfalfa with long inflorescence was stronger than that of alfalfa with short inflorescences. Furthermore, integrative analysis of the transcriptome and proteome indicated that the phenylpropanoid biosynthesis pathway was closely correlated with the structural formation of the inflorescence. Additionally, we identified key genes and proteins associated with lignin biosynthesis based on the differential expressed genes and proteins (DEGs and DEPs) involved in phenylpropanoid biosynthesis. Moreover, targeted hormone metabolome analysis revealed that IAA, GA, and CK play an important role in the peduncle elongation of alfalfa inflorescences. Based on omics analysis, we detected key genes and proteins related to plant hormone biosynthesis and signal transduction. From the WGCNA and WPCNA results, we furthermore screened 28 candidate genes and six key proteins that were correlated with lignin biosynthesis, plant hormone biosynthesis, and signaling pathways. In addition, 19 crucial transcription factors were discovered using correlation analysis that might play a role in regulating candidate genes. This study provides insight into the molecular mechanism of inflorescence elongation in alfalfa and establishes a theoretical foundation for improving alfalfa seed production.

[Response of Relationship Between Microplastic Abundance and Nitrogen Metabolism Function Microorganisms and Genes in Water].

The impact of microplastics (MPs) as a new type of pollutant on water pollution has become a research hotspot. To explore the response relationship between the abundance of MPs and nitrogen metabolism function in a freshwater environment, Lake Ulansuhai was used as the research object; the abundance of MPs in the water was detected using a Zeiss microscope, and the distribution characteristics of nitrogen metabolism functional bacteria and functional genes in the water were analyzed using metagenomics sequencing. The correlation analysis method was used to explore the relationship between the abundance of MPs and nitrogen metabolism functional microorganisms and nitrogen metabolism functional genes. The results showed that the presence of MPs in freshwater environments had a higher impact on Cyanobacteria and Firmicutes as the dominant phyla, and the presence of MPs promoted their enrichment and growth. Among the dominant bacterial genera, MPs promoted the growth of Mycobacterium and inhibited Candidatus_Planktopila more significantly, further indicating that in freshwater environments, MPs affected normal nitrogen metabolism by affecting microbial communities, and pathways such as carbon and nitrogen fixation and denitrification were important pathways for MPs to affect nitrogen metabolism. From the perspective of nitrogen metabolism functional genes, it was found that the abundance of MPs significantly affected some functional genes during nitrification (pmoA-amoA, pmoB-amoB, and pmoC-amoC), denitrification (nirK and napA), and dissimilatory nitrate reduction (nrfA) processes (P < 0.05). Moreover, the influence of MPs abundance on different functional genes in the same pathway of nitrogen metabolism varied, making the impact of MPs on aquatic environments very complex; thus, its harm to the water environment cannot be underestimated.

Functional genes and microorganisms controlling in situ methylmercury production and degradation in marine sediments: A case study in the Eastern China Coastal Seas.

Dominant microorganisms and functional genes, including hgcA, hgcB, merA, and merB, have been identified to be responsible for mercury (Hg) methylation or methylmercury (MeHg) demethylation. However, their in situ correlation with MeHg levels and the processes of Hg methylation and MeHg demethylation in coastal areas remains poorly understood. In this study, four functional genes related to Hg methylation and MeHg demethylation (hgcA, hgcB, merA, and merB) were all detected in the sediments of the Eastern China Coastal Seas (ECCSs) (representative coastal seas highly affected by human activities) using metagenomic approaches. HgcA was identified to be the key gene controlling the in situ net production of MeHg in the ECCSs. Based on metagenomic analysis and incubation experiments, sulfate-reducing bacteria were identified as the dominant microorganisms controlling Hg methylation in the ECCSs. In addition, hgcA gene was positively correlated with the MeHg content and Hg methylation rates, highlighting the potential roles of Hg methylation genes and microorganisms influenced by sediment physicochemical properties in MeHg cycling in the ECCSs. These findings highlighted the necessity of conducting similar studies in other natural systems for elucidating the molecular mechanisms underlying MeHg production in aquatic environments.

Comprehensive profiles of sulfur cycling microbial communities along a mangrove sediment depth.

The sulfur (S) cycle is an important biogeochemical cycle with profound implications for both cellular- and ecosystem-level processes by diverse microorganisms. Mangrove sediments are a hotspot of biogeochemical cycling, especially for the S cycle with high concentrations of S compounds. Previous studies have mainly focused on some specific inorganic S cycling processes without paying specific attention to the overall S-cycling communities and processes as well as organic S metabolism. In this study, we comprehensively analyzed the distribution, ecological network and assembly mechanisms of S cycling microbial communities and their changes with sediment depths using metagenome sequencing data. The results showed that the abundance of gene families involved in sulfur oxidation, assimilatory sulfate reduction, and dimethylsulfoniopropionate (DMSP) cleavage and demethylation decreased with sediment depths, while those involved in S reduction and dimethyl sulfide (DMS) transformation showed an opposite trend. Specifically, glpE, responsible for converting S2O32- to SO32-, showed the highest abundance in the surface sediment and decreased with sediment depths; in contrast, high abundances of dmsA, responsible for converting dimethyl sulfoxide (DMSO) to DMS, were identified and increased with sediment depths. We identified Pseudomonas and Streptomyces as the main S-cycling microorganisms, while Thermococcus could play an import role in microbial network connections in the S-cycling microbial community. Our statistical analysis showed that both taxonomical and functional compositions were generally shaped by stochastic processes, while the functional composition of organic S metabolism showed a transition from stochastic to deterministic processes. This study provides a novel perspective of diversity distribution of S-cycling functions and taxa as well as their potential assembly mechanisms, which has important implications for maintaining mangrove ecosystem functions.

In-situ treatment of gaseous benzene in fixed-bed biofilter with polyurethane foam: Functional population response and benzene transformation pathway.

Volatile organic compounds emitted from landfills posed adverse effect on health. In this study, gaseous benzene was biologically treated using an in-situ biofilter without air pump. Its performance was investigated and the removal efficiency of benzene reached over 90 %. The decrease in the average benzene concentration was consistent with first-order reaction kinetics. Mycolicibacterium dominated the bacterial consortium (41-57 %) throughout the degradation. Annotation of genes by metagenomic analysis helped to deduce the degradation pathways (benzene degradation, catechol ortho-cleavage and meta-cleavage) and to reveal the contribution of different species to the degradation process. In total, 21 kinds of key genes and 13 enzymes were involved in the three modules of benzene transformation. Mycolicibacter icosiumassiliensis and Sphingobium sp. SCG-1 carried multiple functional genes critically involved in benzene biodegradation. These findings provide technical and theoretical support for the in-situ bioremediation of benzene-contaminated soil and waste gas reduction in landfills.

Changing the order and ratio of substrate filling reduced CH4 and N2O emissions from the aerated constructed wetlands.

Constructed wetlands (CWs) have been used to enhance pollutant removal by filling several types of material as substrates. However, research on substrate filling order remains still limited, particularly regarding the effects of greenhouse gas (GHG) emissions. In this study, six CWs were constructed using zeolite and ferric­carbon micro-electrolysis (Fe-C) fillers to evaluate the effect of changing the filling order and ratio on pollutant removal, GHGs emissions, and associated microbial structure. The results showed that the order of substrate filling significantly impacted pollutant removal performance on CWs. Specifically, CWs filled with zeolite in the top layer exhibited superior NH4+-N removal compared to those filled in the lower layer. Moreover, the highest NH4+-N removal (95.0 % ± 1.9 %) was observed in CWs with a zeolite to Fe-C volume ratio of 8:2 (CWZe-1). Moreover, zeolite-filled at the top had lower GHGs emissions, with the lowest CH4 (0.22 ± 0.10 mg m-2 h-1) and N2O (167.03 ± 61.40 µg m-2 h-1) fluxes in the CWZe-1. In addition, it is worth noting that N2O is the major contributor to integrated global warming potential (GWP) in the six CWs, accounting for 81.7 %-90.8 %. The upper layer of CWs filled with zeolite exhibited higher abundances of nirK, nirS and nosZ genes. The order in which the substrate was filled affected the microbial community structure and the upper layer of CWs filled with zeolite had higher relative abundance of nitrifying genera (Nitrobacter, Nitrosomonas) and denitrifying genera (Zoogloea, Denitratisoma). Additionally, N2O emission was reduced by approximately 41.2 %-64.4 % when the location of the aeration of the CWs was changed from the bottom to the middle. This study showed that both the order of filling the substrate and the aeration position significantly affected the GHGs emissions from CWs, and that CWs had lower GHGs emissions when zeolites were filled in the upper layer and the aeration position was in the middle.

Effect of conventional and biodegradable microplastics on the soil-soybean system: A perspective on rhizosphere microbial community and soil element cycling.

As an exogenous carbon input, microplastics (MPs), especially biodegradable MPs, may significantly disrupt soil microbial communities and soil element cycling (CNPS cycling), but few studies have focused on this. Here, we focused on assessing the effects of conventional low-density polyethylene (LDPE), biodegradable polybutylene adipate terephthalate (PBAT), and polylactic acid (PLA) MPs on rhizosphere microbial communities and CNPS cycling in a soil-soybean system. The results showed that PBAT-MPs and PLA-MPs were more detrimental to soybean growth than LDPE-MPs, resulting in a reduction in shoot nitrogen (14.05% and 11.84%) and shoot biomass (33.80% and 28.09%) at the podding stage. In addition, dissolved organic carbon (DOC) increased by 20.91% and 66.59%, while nitrate nitrogen (NO3--N) significantly decreased by 56.91% and 69.65% in soils treated with PBAT-MPs and PLA-MPs, respectively. PBAT-MPs and PLA-MPs mainly enhanced copiotrophic bacteria (Proteobacteria) and suppressed oligotrophic bacteria (Verrucomicrobiota, Gemmatimonadota, etc.), increasing the abundance of CNPS cycling-related functional genes. LDPE-MPs tended to enrich oligotrophic bacteria (Verrucomicrobiota, etc.) and decrease the abundance of CNPS cycling-related functional genes. Correlation analysis revealed that MPs with different degradation properties selectively affected the composition and function of the bacterial community, resulting in changes in the availability of soil nutrients (especially NO3--N). Redundancy analysis further indicated that NO3--N was the primary constraining factor for soybean growth. This study provides a new perspective for revealing the underlying ecological effects of MPs on soil-plant systems.

Insights into the seasonal changes in the taxonomic and functional diversity of bacteria in the eastern Arabian Sea: Shotgun metagenomics approach.

The eastern Arabian Sea (EAS) is known for its unique oceanographic features such as the seasonal monsoonal winds, upwelling of nutrient-rich waters and a significant increase in primary productivity during the monsoon season. In this study, we utilised the shotgun metagenomics approach to determine the seasonal variations in bacterial taxonomic and functional profiles during the non-monsoon and monsoon seasons in the EAS. Significant seasonal variations in the bacterial community structure were observed at the phylum and genera levels. These findings also correspond with seasonal shifts in the functional profiles of the bacterial communities based on the variations of genes encoding enzymes associated with different metabolic pathways. Pronounced seasonal variation of bacterial taxa was evident with an increased abundance of Idiomarina, Marinobacter, Psychrobacter and Alteromonas of Proteobacteria, Bacillus and Staphylococcus of Firmicutes during the non-monsoon season. These taxa were linked to elevated nucleotide and amino acid biosynthesis, amino acid and lipid degradation. Conversely, during the monsoon, the taxa composition changed with Alteromonas, Candidatus Pelagibacter of Proteobacteria and Cyanobacteria Synechococcus; contributing largely to the amino acid and lipid biosynthesis, fermentation and inorganic nutrient metabolism which was evident from functional analysis. Regression analysis confirmed that increased seasonal primary productivity significantly influenced the abundance of genes associated with carbohydrate, protein and lipid metabolism. These highlight the pivotal role of seasonal changes in primary productivity in shaping the bacterial communities, their functional profiles and driving the biogeochemical cycling in the EAS.