Microbial community structure and co-occurrence are essential for methanogenesis and its contribution to phenanthrene degradation in paddy soil

Underwater light source changes microecosystem constructed by Vallisneria spinulosa Yan for water restoration: Efficiency of water purification, characteristics of growth, and rhizosphere

Submerged macrophytes are effective in ecological restoration of water bodies polluted by nitrogen and phosphorus, and its restoration capacity depends on underwater illumination condition. This study explored the influencing mechanism of illumination on Vallisneria spinulosa Yan (V. spinulosa Yan) for water restoration. Addition of underwater light source increased the total nitrogen, ammonia nitrogen, total phosphorus, and phosphate removal loads of the V. spinulosa Yan growth system by 61.5, 39.2, 8.5, and 5.0 mg m-2 d-1, respectively. Meanwhile, the growth of V. spinulosa Yan was obviously promoted, even with high water turbidity. Although the biological nitrogen removal processes were inhibited by adding underwater light source, the growth of V. spinulosa Yan can be significantly improved, thus enhancing the efficiency of water purification via the absorption of nitrogen and phosphorus by V. spinulosa Yan. This study provides a theoretical foundation and technical support for application of submerged macrophytes in ecological water restoration.

Changes in community structure and microbiological risks in a small stream after receiving treated shale gas wastewater for two years

Discharge of treated shale gas wastewater is becoming prevalent in the Sichuan Basin in China, and the resulting potential environmental impacts have raised concern. In this study, the responses of microbial community in the receiving water to discharge of treated shale gas wastewater were assessed during a two-year study period, covering two wet seasons and one dry season. The results showed that the discharge of treated shale gas wastewater had no significant effects on alpha diversity in the two wet seasons, but had significant effects in the dry season after 15 months of discharge. Obvious changes in microbial community structure were observed in all three seasons at the downstream sites near the wastewater outfall, as compared to the control site. Multimetric indices indicated that the impacts of wastewater discharge on microbial ecosystem occurred with the extension of the discharge period. Moreover, special attention was given to the microbiological risks associated with antibiotic resistance genes (ARGs), virulence factor genes (VFGs), and pathogenic antibiotic resistant bacteria (PARBs) in the dry season in sediments of the receiving water. At downstream sites near the outfall, five subtypes of ARGs and seven VFGs showed a significant increase in relative abundance. Forty-two PARBs carrying ARGs and VFGs were detected, and three PARBs (Pseudomonas aeruginosa, Pseudomonas stutzeri and Pseudomonas fluorescens) increased obviously in relative abundance at the downstream site near the outfall. In conclusion, long-term wastewater discharge had effects on the microbial community, and limited microbiological risks existed in the receiving waters.

Exposure to three herbicide mixtures influenced maize root-associated microbial community structure, function and the network complexity

Herbicide mixtures are a new and effective agricultural strategy for managing suppress weed resistance and have been widely used in controlling weeding growth in maize fields. However, the potential ecotoxicological impact of these mixtures on the microbial community structure and function within various root-associated niches, remains inadequately understood. Here, the effects of nicosulfuron, mesotrione and atrazine on soil enzyme activity and microbial community structure and function were investigated when applied alone and in combination. The findings indicated that herbicide mixtures exhibit a prolonged half-life compared to single herbicides. Ecological niches are the major factor influencing the structure and functions of the microbial community, with the rhizosphere exhibiting a more intensive response to herbicide stress. Herbicides significantly inhibited the activities of soil functional enzymes, including dehydrogenase, urease and sucrose in the short-term. Single herbicide did not drastically influence the alpha or beta diversity of the soil bacterial community, but herbicide mixtures significantly increased the richness of the fungal community. Meanwhile, the key functional microbial populations, such as Pseudomonas and Enterobacteriaceae, were significantly altered by herbicide stress. Both individual and combined use of the three herbicides reduced the complexity and stability of the bacterial network but increased the interspecific cooperations of fungal community in the rhizosphere. Moreover, by quantification of residual herbicide concentrations in the soil, we showed that the degradation period of the herbicide mixture was longer than that of single herbicides. Herbicide mixtures increased the contents of NO3--N and NH4+-N in the soil in the short-term. Overall, our study provided a comprehensive insight into the response of maize root-associated microbial communities to herbicide mixtures and facilitated the assessment of the ecological risks posed by herbicide mixtures to the agricultural environment from an agricultural sustainability perspective.

Fe-loaded biochar thin-layer capping for the remediation of sediment polluted with nitrate and bisphenol A: Insight into interdomain microbial interactions

The information on the collaborative removal of nitrate and trace organic contaminants in the thin-layer capping system covered with Fe-loaded biochar (FeBC) is limited. The community changes of bacteria, archaea and fungi, and their co-occurrence patterns during the remediation processes are also unknown. In this study, the optimized biochar (BC) and FeBC were selected as the capping materials in a batch experiment for the remediation of overlying water and sediment polluted with nitrate and bisphenol A (BPA). The community structure and metabolic activities of bacteria, archaea and fungi were investigated. During the incubation (28 d), the nitrate in overlying water decreased from 29.6 to 11.0 mg L-1 in the FeBC group, 2.9 and 1.8 times higher than the removal efficiencies in Control and BC group. The nitrate in the sediment declined from 5.03 to 0.75 mg kg-1 in the FeBC group, 1.3 and 1.1 times higher than those in Control and BC group. The BPA content in the overlying water in BC group and FeBC group maintained below 0.4 mg L-1 during incubation, signally lower than in the Control group. After capping with FeBC, a series of species in bacteria, archaea and fungi could collaboratively contribute to the removal of nitrate and BPA. In the FeBC group, more metabolism pathways related to nitrogen metabolism (KO00910) and Bisphenol degradation (KO00363) were generated. The co-occurrence network analysis manifested a more intense interaction within bacteria communities than archaea and fungi. Proteobacteria, Firmicutes, Actinobacteria in bacteria, and Crenarchaeota in archaea are verified keystone species in co-occurrence network construction. The information demonstrated the improved pollutant attenuation by optimizing biochar properties, improving microbial diversity and upgrading microbial metabolic activities. Our results are of significance in providing theoretical guidance on the remediation of sediments polluted with nitrate and trace organic contaminants.

Quantitative analysis of TCE biodegradation pathway in landfill cover utilizing continuous monitoring, droplet digital PCR and multi-omics sequencing technology

The remediation of volatile chlorinated hydrocarbons in the quasi-vadose zone has become a significant challenge. We applied an integrated approach to assess the biodegradability of trichloroethylene to identify the biotransformation mechanism. The formation of the functional zone biochemical layer was assessed by analyzing the distribution of landfill gas, physical and chemical properties of cover soil, spatial-temporal variations of micro-ecology, biodegradability of landfill cover soil and distributional difference metabolic pathway. Real-time online monitoring showed that trichloroethylene continuously undergoes anaerobic dichlorination and simultaneous aerobic/anaerobic conversion-aerobic co-metabolic degradation on the vertical gradient of the landfill cover system and reduction in trans-1,2-dichloroethylene in the anoxic zone but not 1,1-dichloroethylene. PCR and diversity sequencing revealed the abundance and spatial distribution of known dichlorination-related genes within the landfill cover, with 6.61 ± 0.25 × 104-6.78 ± 0.09 × 106 and 1.17 ± 0.78 × 103-7.82 ± 0.07 × 105 copies per g/soil of pmoA and tceA, respectively. In addition, dominant bacteria and diversity were significantly linked with physicochemical factors, and Mesorhizobium, Pseudoxanthomonas and Gemmatimonas were responsible for biodegradation in the aerobic, anoxic and anaerobic zones. Metagenome sequencing identified 6 degradation pathways of trichloroethylene that may occur in the landfill cover; the main pathway was incomplete dechlorination accompanied by cometabolic degradation. These results indicate that the anoxic zone is important for trichloroethylene degradation.

Microbial electron flow promotes naphthalene degradation in anaerobic digestion in the presence of nitrate electron acceptor: Focus on electron flow regulation and microbial interaction succession

Microbial electron flow (MEF) is produced from microbial degradation of organic compounds. Regulating MEF to promote organic pollutants biodegradation such as naphthalene (Nap) is a potential way but remains a lack of theoretical basis. Here, we regulated MEF by adding electron acceptor NO3- to achieve 2.6 times increase of Nap biodegradation with cyclodextrin as co-metabolism carbon source. With the NO3- addition, the genes inhibited by Nap of electron generation significantly up-regulated. Especially, key genes ubiD and nahD for anaerobic Nap degradation significantly up-regulated respectively 3.7 times and 6.7 times. Moreover, the ability of electron transfer in MEF was also improved consistent with 7.2 times increase of electron transfer system (ETS) activity. Furthermore, total 60 metagenome-assembled genomes (MAGs) were reconstructed through the metagenomic sequencing data with assembly and binning strategies. Interestingly, it was also first found that the Klebsiella MAG. SDU (Shandong University) 14 had the ability of simultaneous Nap biodegradation and denitrification. Our results firstly offered an effective method of regulating MEF to promote polycyclic aromatic hydrocarbons (PAHs) degradation and simultaneous methanogenesis.

Magnetic loofah sponge biochar facilitates microbial interspecies cooperation in surface and subsurface sediments for enhanced PAH biodegradation

Magnetic biochar had been used for the bioremediation of polycyclic aromatic hydrocarbon (PAH)-contaminated sediments. However, the long-term remediation pattern of vertical stratification driven by the application of magnetic biochar and the assembly of microbes had received little attention. In this study, magnetic loofah sponge biochar (MagLsBC), magnetic iron oxide (MagOx) and magnetic coconut shell activated carbon (MagCoAC) were applied for the 900-day remediation of contaminated sediments. Significant (p < 0.05) PAH biodegradation was observed in both the surface and subsurface sediments with MagLsBC addition. However, enhanced PAH biodegradation was observed only in the surface sediments with MagOx and MagCoAC treatments. Magnetotactic bacteria (Magnetococcus) was dominant genera in surface sediments and indigenous PAH degradation bacteria were more abundant in subsurface sediments of MagLsBC relative to other bacterial communities. The network interaction between microbes in surface and subsurface sediments with MagLsBC treatments was a less complex and tighter than those with MagCoAC, MagOx or Control treatments. Long-distance electron transfer rates could be enhanced through cooperation between magnetotactic bacteria and indigenous degradation bacteria, thus accelerating PAH degradation in sediment with MagLsBC treatment, especially in the underlying sediment.

Significant roles of core prokaryotic microbiota across soil profiles in an organic contaminated site: Insight into microbial assemblage, co-occurrence patterns, and potentially key ecological functions

Extreme environmental disturbances induced by organic contaminated sites impose serious impacts on soil microbiomes. However, our understanding of the responses of the core microbiota and its ecological roles in organic contaminated sites is limited. In this study, we took a typical organic contaminated site as an example and investigated the composition and structure, assembly mechanisms of core taxa and their roles in key ecological functions across soil profiles. Results presented that core microbiota with a considerably lower number of species (7.93%) than occasional taxa presented comparatively high relative abundances (38.04%) yet, which was mainly comprised of phyla Proteobacteria (49.21%), Actinobacteria (12.36%), Chloroflexi (10.63%), and Firmicutes (8.21%). Furthermore, core microbiota was more influenced by geographical differentiation than environmental filtering, which possessed broader niche widths and stronger phylogenetic signals for ecological preferences than occasional taxa. Null modelling suggested that stochastic processes dominated the assembly of the core taxa and maintained a stable proportion along soil depths. Core microbiota had a greater impact on microbial community stability and possessed higher functional redundancy than occasional taxa. Additionally, the structural equation model illustrated that core taxa played pivotal roles in degrading organic contaminants and maintaining key biogeochemical cycles potentially. Overall, this study deepens our knowledge of the ecology of core microbiota under complicated environmental conditions in organic contaminated sites, and provides a fundamental basis for preserving and potentially utilizing core microbiota to maintain soil health.

Low-temperature corn straw-degrading bacterial agent and moisture effects on indigenous microbes

While the in situ return of corn straw can improve soil fertility and farmland ecology, additional bacterial agents are required in low-temperature areas of northern China to accelerate straw degradation. Moisture is an important factor affecting microbial activity; however, owing to a lack of bacterial agents adapted to low-temperature complex soil environments, the effects of soil moisture on the interaction between exogenous bacterial agents and indigenous soil microorganisms remain unclear. To this end, we explored the effect of the compound bacterial agent CFF constructed using Pseudomonas putida and Acinetobacter lwoffii, developed to degrade corn straw in low-temperature soils (15 °C), on indigenous bacterial and fungal communities under dry (10% moisture content), slightly wet (20%), and wet (30%) soil-moisture conditions. The results showed that CFF application significantly affected the α-diversity of bacterial communities and changed both bacterial and fungal community structures, enhancing the correlation between microbial communities and soil-moisture content. CFF application also changed the network structure and the species of key microbial taxa, promoting more linkages among microbial genera. Notably, with an increase in soil moisture, CFF enhanced the rate of corn straw degradation by inducing positive interactions between bacterial and fungal genera and enriching straw degradation-related microbial taxa. Overall, our study demonstrates the alteration of indigenous microbial communities using bacterial agents (CFF) to overcome the limitations of indigenous microorganisms for in situ straw-return agriculture in low-temperature areas. KEY POINTS: • Low-temperature and variable moisture conditions (10-30%) were compared • Soil microbial network structure and linkages between genera were altered • CFF improves straw degradation via positive interactions between soil microbes.

Evidence for nontraditional mcr-containing archaea contributing to biological methanogenesis in geothermal springs

Recent discoveries of methyl-coenzyme M reductase-encoding genes (mcr) in uncultured archaea beyond traditional euryarchaeotal methanogens have reshaped our view of methanogenesis. However, whether any of these nontraditional archaea perform methanogenesis remains elusive. Here, we report field and microcosm experiments based on ¹³C-tracer labeling and genome-resolved metagenomics and metatranscriptomics, revealing that nontraditional archaea are predominant active methane producers in two geothermal springs. Archaeoglobales performed methanogenesis from methanol and may exhibit adaptability in using methylotrophic and hydrogenotrophic pathways based on temperature/substrate availability. A five-year field survey found Candidatus Nezhaarchaeota to be the predominant mcr-containing archaea inhabiting the springs; genomic inference and mcr expression under methanogenic conditions strongly suggested that this lineage mediated hydrogenotrophic methanogenesis in situ. Methanogenesis was temperature-sensitive , with a preference for methylotrophic over hydrogenotrophic pathways when incubation temperatures increased from 65° to 75°C. This study demonstrates an anoxic ecosystem wherein methanogenesis is primarily driven by archaea beyond known methanogens, highlighting diverse nontraditional mcr-containing archaea as previously unrecognized methane sources.

Arbuscular mycorrhizal fungi alter rhizosphere bacterial community characteristics to improve Cr tolerance of Acorus calamus

Arbuscular mycorrhizal fungi (AMF) can improve plant tolerance to heavy metal stress in terrestrial ecosystems. However, in wetland ecosystems, AMF can improve the tolerance of wetland plants to heavy metals by changing the structure and composition of rhizosphere bacterial communities, which is still rarely studied. In this study, we investigated the effects of AMF on the structure and composition of bacterial communities in the rhizosphere of plants under different chromium concentrations. The results showed that Cr(Ⅵ) concentration in Acorus calamus. rhizosphere soil decreased by 12.6 % (5.6-21.7 %) on average after AMF inoculation, At the same time, it promoted the uptake of nutrients by A. calamus and increased soil carbon input. In addition, Cr stress decreased the bacterial community diversity and abundance index by 9.8 % (1.6-18.1 %) and 24.5 % (17.3-27.6 %) on average. On the contrary, the rhizosphere soil bacterial diversity and abundance index increased by 7.3 % (2.2-19.1 %) and 13.9 % (6.0-20.9 %) on average after AMF inoculation. Moreover, compared with the non-inoculated AMF group, the bacterial community structure of A. calamus rhizosphere changed by 24.6 % under Cr stress, The common number of species increased by 6.4 %. In addition, after inoculation of AMF significantly promote the growth of a large number of bacteria related to organic degradation, plant growth, and oxidative stress, increased soil carbon input improved the soil microenvironment. Meanwhile, After AMF inoculation, the Number of edges, Number of Nodes, Average degree, and Average Path length in the symbiotic network of rhizosphere soil bacterial community increased by 34.6 %, 10 %, 44.3 %, and 26.4 %, respectively. Therefore, it offers a possibility that AMF can enhance the tolerance of wetland plants to soil Cr pollution by improving the structure and composition of bacterial communities in the rhizosphere soils of wetland plants, which provide a basis for wetland plants to repair soil Cr pollution.

Toxicity sharing model of earthworm intestinal microbiome reveals shared functional genes are more powerful than species in resisting pesticide stress

Earthworm intestinal bacteria and indigenous soil bacteria work closely during various biochemical processes and play a crucial role in maintaining the internal stability of the soil environment. However, the response mechanism of these bacterial communities to external pesticide disturbance is unknown. In this study, soil and earthworm gut contents were metagenomically sequenced after exposure to various concentrations of nitrochlorobenzene (0-1026.7 mg kg^-1). A high degree of similarity was found between the microbial community composition and abundance in the worm gut and soil, both of which decreased significantly (P < 0.05) under elevated pesticide stress. The toxicity sharing model (TSM) showed that the toxicity sharing capacity was 97.4-125.7 % and 100.4-130.2 % for E_genes (genes in the worm gut) and E_met(degradation genes in the worm gut) in the earthworm intestinal microbiome, respectively. This indicated that the earthworm intestinal microbiome assisted in relieving the pesticide toxicity of the indigenous soil microbiome. This study showed that the TSM could quantitatively describe the toxic effect of pesticides on the earthworm intestinal microbiome. It provides a new analytical model for investigating the ecological alliance between earthworm intestinal microbiome and indigenous soil microbiome under pesticide stress while contributing a more profound understanding of the potential to use earthworms to mitigate pesticide pollution in soils and develop earthworm-based soil remediation techniques.

Early stage biofilm formation on bio-based microplastics in a freshwater reservoir

Bio-based plastics (BP) produced from renewable biomass resources, such as high-density polyethylene (HDPE), polylactic acid (PLA) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), is currently increasing in terms of both products and applications. However, their biodegradability and environmental fate are not yet fully understood, especially in freshwaters. Here, we present the results of an in-situ study in a freshwater reservoir, where we submerged HDPE, PLA and PHBV microscale BP (mBP) in dialysis bags to enable exchange of small organic and inorganic molecules, including nutrients, with the surrounding water. After one and two months, the bacterial biofilm that formed on each mBP was characterised by 16S rRNA amplicon sequencing. After two-months, Oxalobacteraceae, Pedosphaeraceae, Flavobacteriaceae (Flavobacterium) and Chitinophagaceae (Ferruginibacter) had increased by up to four times. Both these and other common members (≥1 % relative total biomass) of the microbial community were similarly abundant on all mBP. Low-abundance (0.3-1 %) bacterial taxa, however, were significantly more diverse and differed on each mBP. Notably, some low-abundance families and genera increased on specific materials, e.g. Sphingomonadaceae on HDPE, Sphingobacteriaceae on PHBV, Gemmatimonas and Crenothrix on PLA. Overall, abundant bacteria were regarded as a pioneering community, while low-abundance bacteria were more diverse and preferred mBP types in the early stages of biofilm formation on mBP. It could be influenced by the environmental conditions, where nutrient levels and low temperatures might shape the low-abundance of attached bacterial communities than the plastic material itself.

Effects of Polyethylene Microplastics and Phenanthrene on Soil Properties, Enzyme Activities and Bacterial Communities

Microplastics (MPs) or polycyclic aromatic hydrocarbons (PAHs) pollution has received increasing concern due to their ubiquitous distribution and potential risks in soils. However, nothing is known about the influences of PAHs-MPs combined pollution on soil ecosystems. To address the knowledge gap, a 1-year soil microcosm experiment was conducted to systematically investigate the single and combined effect of polyethylene (PE) /phenanthrene (PHE) on soil chemical properties, enzymatic activities and bacterial communities (i.e., diversity, composition and function). Results showed that PE and PHE-PE significantly decreased soil pH. The available phosphorus (AP) and neutral phosphatase activity were not considerably changed by PHE, PE and PHE-PE. Significant enhancement of dehydrogenase activity in a PHE-PE amended system might be due to the degradation of PHE by indigenous bacteria (i.e., Sphingomonas, Sphingobium), and PE could enhance this stimulative effect. PHE and PHE-PE led to a slight increase in soil organic matter (SOM) and fluorescein diacetate hydrolase (FDAse) activity but a decrease in available nitrogen (AN) and urease activity. PE significantly enhanced the functions of nitrogen cycle and metabolism, reducing SOM/AN contents but increasing urease/FDAse activities. There were insignificant impacts on overall community diversity and composition in treated samples, although some bacterial genera were significantly stimulated or attenuated with treatments. In conclusion, the addition of PHE and PE influenced the soil chemical properties, enzymatic activities and bacterial community diversity/composition to some extent. The significantly positive effect of PE on the nitrogen cycle and on metabolic function might lead to the conspicuous alterations in SOM/AN contents and urease/FDAse activities. This study may provide new basic information for understanding the ecological risk of PAHs-MPs combined pollution in soils.

Sulfonamide-metabolizing microorganisms and mechanisms in antibiotic-contaminated wetland sediments revealed by stable isotope probing and metagenomics

Sulfonamide (SA) antibiotics are ubiquitous pollutants in livestock breeding and aquaculture wastewaters, which increases the propagation of antibiotic resistance genes. Microbes with the ability to degrade SA play important roles in SA dissipation, but their diversity and the degradation mechanism in the field remain unclear. In the present study, we employed DNA-stable isotope probing (SIP) combined with metagenomics to explore the active microorganisms and mechanisms of SA biodegradation in antibiotic-contaminated wetland sediments. DNA-SIP revealed various SA-assimilating bacteria dominated by members of Proteobacteria, such as Bradyrhizobium, Gemmatimonas, and unclassified Burkholderiaceae. Both sulfadiazine and sulfamethoxazole were dissipated mainly through the initial ipso-hydroxylation, and were driven by similar microbes. sadA gene, which encodes an NADH-dependent monooxygenase, was enriched in the ¹³C heavy DNA, confirming its catalytic capacity for the initial ipso-hydroxylation of SA in sediments. In addition, some genes encoding dioxygenases were also proposed to participate in SA hydroxylation and aromatic ring cleavage based on metagenomics analysis, which might play an important role in SA metabolism in the sediment ecosystem when Proteobacteria was the dominant active bacteria. Our work elucidates the ecological roles of uncultured microorganisms in their natural habitats and gives a deeper understanding of in-situ SA biodegradation mechanisms.

Remediation of PAHs contaminated industrial soils by hypochlorous acid: performance and mechanisms

Polycyclic aromatic hydrocarbons (PAHs) mainly originate from incomplete combustion of organic substances and are carcinogenic, mutagenic and teratogenetic, posing a high risk to the ecosystem and human health. The remediation of soils contaminated with PAHs has aroused wide public concern. In this study, hypochlorous acid (HOCl) was applied to realize PAHs removal from industrial contaminated soil with an extremely high degradation efficiency of 93.33% when the initial chlorine concentration was 5000 mg L⁻¹. The degradation behavior of PAHs by HOCl oxidation was investigated in detail. Parameters including chlorine dosage, pH and temperature that had effects on the degradation process were evaluated systematically. The removal of PAHs was followed well with the pseudo-first-order kinetic model. It is found that HOCl and OH˙ were major contributors to the degradation products of chlorinated and oxygenated PAHs. This research provided an easy-operating and energy-saving way to realize the remediation of PAHs contaminated industrial soil practically with high efficiency.

An extremely high degradation efficiency of 93.3% was realized for PAHs in contaminated industrial soil by HOCl oxidation.

Biogeography, assembly processes and species coexistence patterns of microbial communities in metalloids-laden soils around mining and smelting sites

Microbes are important component in terrestrial ecosystem, which are believed to play vital roles in biogeochemical cycles of metalloids in mining and smelting surroundings. Many studies on microbial diversity and structures have been investigated around mining and smelting sites, whereas the ecological processes and co-occurrence patterns that influence the biogeographic distributions of microbial communities is yet poorly understood. Herein, microbial biogeography, assembly mechanism and co-occurrence pattern around mining and smelting zone were systematically unraveled using 16S rRNA gene sequencing. The 66 microbial phyla co-occurring across all the samples were dominated by Proteobacteria, Chloroflexi, Acidobacteria and Crenarchaeota. Obvious distance-decay (r = 0.3448, p < 0.001) of microbial community was observed across geographic distances. Differences in microbial communities were driven by the joint impacts of soil factors, spatial and metalloids levels. Dispersal limitation dominated the microbial assemblies in whole, SC and GX sites while homogeneous selection governed that in YN site. The changes in pH and Sb level significantly influenced the deterministic and stochastic processes of microbial communities. Network analysis suggested a typical module distribution, which had apparent ecological links among taxa in modules. This study provides first insight of the mechanism to maintain microbial diversity in metalloids-laden biospheres.

Co-metabolic Effect of Glucose on Methane Production and Phenanthrene Removal in an Enriched Phenanthrene-Degrading Consortium Under Methanogenesis

Anaerobic digestion is used to treat diverse waste classes, and polycyclic aromatic hydrocarbons (PAHs) are a class of refractory compounds that common in wastes treated using anaerobic digestion. In this study, a microbial consortium with the ability to degrade phenanthrene under methanogenesis was enriched from paddy soil to investigate the cometabolic effect of glucose on methane (CH₄) production and phenanthrene (a representative PAH) degradation under methanogenic conditions. The addition of glucose enhanced the CH₄ production rate (from 0.37 to 2.25mg⋅L^-1⋅d^-1) but had no influence on the degradation rate of phenanthrene. Moreover, glucose addition significantly decreased the microbial α-diversity (from 2.59 to 1.30) of the enriched consortium but showed no significant effect on the microbial community (R ²=0.39, p=0.10), archaeal community (R ²=0.48, p=0.10), or functional profile (R ²=0.48, p=0.10). The relative abundance of genes involved in the degradation of aromatic compounds showed a decreasing tendency with the addition of glucose, whereas that of genes related to CH₄ synthesis was not affected. Additionally, the abundance of genes related to the acetate pathway was the highest among the four types of CH₄ synthesis pathways detected in the enriched consortium, which averagely accounted for 48.24% of the total CH₄ synthesis pathway, indicating that the acetate pathway is dominant in this phenanthrene-degrading system during methanogenesis. Our results reveal that achieving an ideal effect is diffcult via co-metabolism in a single-stage digestion system of PAH under methanogenesis; thus, other anaerobic systems with higher PAH removal efficiency should be combined with methanogenic digestion, assembling a multistage pattern to enhance the PAH removal rate and CH₄ production in anaerobic digestion.