Depth-resolved microbial diversity and functional profiles of trichloroethylene-contaminated soils for Biolog EcoPlate-based biostimulation strategy

Higher thermal remediation temperature facilitates the sequential bioaugmented reductive dechlorination

The coupling of thermal remediation with microbial reductive dechlorination (MRD) has shown promising potential for the cleanup of chlorinated solvent contaminated sites. In this study, thermal treatment and bioaugmentation were applied in series, where prior higher thermal remediation temperature led to improved TCE dechlorination performance with both better organohalide-respiring bacteria (OHRB) colonization and electron donor availability. The 60 °C was found to be a key temperature point where the promotion effect became obvious. Amplicon sequencing and co-occurrence network analysis demonstrated that temperature was a more dominating factor than bioaugmentation that impacted microbial community structure. Higher temperature of prior thermal treatment resulted in the decrease of richness, diversity of indigenous microbial communities, and simplified the network structure, which benefited the build-up of newcoming microorganisms during bioaugmentation. Thus, the abundance of Desulfitobacterium increased from 0.11 % (25 °C) to 3.10 % (90 °C). Meanwhile, released volatile fatty acids (VFAs) during thermal remediation functioned as electron donors and boosted MRD. Our results provided temperature-specific information on synergistic effect of sequential thermal remediation and bioaugmentation, which contributed to better implementation of the coupled technologies in chloroethene-impacted sites.

The mechanisms of yeast extracellular metabolites in stimulating microbial degradation of trichloroethylene: Physiological characteristics and omics analysis

The biodegradation of Trichloroethylene (TCE) is limited by low microbial metabolic capacity but can be enhanced through biostimulation strategies. This study explored the physiological effects and potential molecular mechanisms of the yeast Yarrowia lipolytica extracellular metabolites (YEMs) on the degradation of TCE by Acinetobacter LT1. Results indicated that YEMs stimulated the efficiency of strain LT1 by 50.28%. At the physiological level, YEMs exhibited protective effects on cell morphology, reduced oxidative stress, lessened membrane damage, and enhanced energy production and conversion. Analysis of omics results revealed that the regulation of various metabolic pathways by YEMs improved the degradation of TCE. Furthermore, RT-qPCR showed that the genes encoding YhhW protein in TCE stress and YEMs stimulation groups were 1.72 and 3.22 times the control group, respectively. Molecular docking results showed that the conformation of YhhW after binding to TCE changed into a more active form, which enhanced enzyme activity. Therefore, it is speculated that YhhW is the primary degradative enzyme involved in the process of YEMs stimulating strain LT1 to degrade TCE. These results reveal how YEMs induce strain LT1 to enhance TCE degradation.

Soil microbial communities and degradation of pesticides in greenhouse effluent through a woodchip bioreactor

Pesticides, including insecticides and fungicides, are major contaminants in the effluent from intensive agricultural systems, such as greenhouses. Because of their constant use and persistence, some pesticides can accumulate in soil and/or run off into adjacent waterways. Microbial communities in soil can degrade some pesticides, and bioreactors with enhanced microbial communities have the potential to facilitate decontamination before the effluent is released into the environment. In this study, we sampled the soil along a gradient from immediately below greenhouses, into, through and below a bioreactor. Multi-analyte pesticide screening was undertaken along with shotgun metagenomic sequencing, to assess microbial community taxonomic profiles and metabolic pathway responses for functional analysis. Two insecticides (imidacloprid and fipronil) and nine fungicides were identified in the soil samples, with a general decrease in most pesticides with increasing distance from the greenhouses. Diversity indexes of taxonomic profiles show changes in the microbial community along the gradient. In particular, microbial communities were significantly different in the bioreactor, with lower Shannon diversity compared to immediately below the greenhouses, in the channels leading into the bioreactor and further downstream. Metabolic pathway analysis revealed significant changes in a wide range of core housekeeping genes such as protein/amino acid synthesis and lipid/fatty acid biosynthesis among the sampling sites. The result demonstrates that the composition and potential functional pathways of the microbial community shifted towards an increased tendency for phytol and contaminant degradation in the bioreactor, facilitated by high organic matter content. This highlights the potential to use enhanced microbial communities within bioreactors to reduce contamination by some pesticides in sediment receiving run-off from greenhouses.

Uncovering the microbial community structure and physiological profiles of terrestrial mud volcanoes: A comprehensive metagenomic insight towards their trichloroethylene biodegradation potentiality

Mud volcanoes are dynamic geological features releasing methane (CH4), carbon dioxide (CO2), and hydrocarbons, harboring diverse methane and hydrocarbon-degrading microbes. However, the potential application of these microbial communities in chlorinated hydrocarbons bioremediation purposes such as trichloroethylene (TCE) has not yet been explored. Hence, this study investigated the mud volcano's microbial diversity functional potentiality in TCE degradation as well as their eco-physiological profiling using metabolic activity. Geochemical analysis of the mud volcano samples revealed variations in pH, temperature, and oxidation-reduction potential, indicating diverse environmental conditions. The Biolog Ecoplate™ carbon substrates utilization pattern showed that the Tween 80 was highly consumed by mud volcanic microbial community. Similarly, MicroResp® analysis results demonstrated that presence of additive C-substrates condition might enhanced the cellular respiration process within mud-volcanic microbial community. Full-length 16 S rRNA sequencing identified Proteobacteria as the dominant phylum, with genera like Pseudomonas and Hydrogenophaga associated with chloroalkane degradation, and methanotrophic bacteria such as Methylomicrobium and Methylophaga linked to methane oxidation. Functional analysis uncovered diverse metabolic functions, including sulfur and methane metabolism and hydrocarbon degradation, with specific genes involved in methane oxidation and sulfur metabolism. These findings provide insights into the microbial diversity and metabolic capabilities of mud volcano ecosystems, which could facilitate their effective application in the bioremediation of chlorinated compounds.

Exploring bacterial community assembly in vadose and saturated zone soil for tailored bioremediation of a long-term hydrocarbon-contaminated site

Indigenous soil microbial communities play a pivotal role in the in situ bioremediation of contaminated sites. However, research on the distribution characteristics of microbial communities at various soil depths remains limited. In particular, there is little information on the assembly of microbial communities, especially those with degradation potential, in the vadose and saturated zones of hydrocarbon-contaminated sites. In this study, 18 soil samples were collected from the vadose zone and saturated zone at a long-term hydrocarbon-contaminated site. The diversity, composition, and driving factors of assembly of the soil bacterial community were determined by high-throughput sequencing analysis. Species richness and diversity were significantly higher in the vadose zone soils than in the saturated zone soils. Significant differences in abundance at both the phylum and genus levels were observed between the two zones. Soil bacterial community assembly was driven by the combination of pollution stress and nutrients in the vadose zone but by nutrient limitations in the saturated zone. The abundance of dechlorinating bacteria was greater in the saturated zone soils than in the vadose zone soils. Compared with contaminant concentrations, nutrient levels had a more pronounced impact on the abundance of dechlorinating bacteria. In addition, the interactions among dechlorinating bacterial populations were stronger in the saturated zone soils than in the vadose zone soils. These findings underscore the importance of comprehensively understanding indigenous microbial communities, especially those with degradation potential, across different soil layers to devise specific, effective in situ bioremediation strategies for contaminated sites.

Unveiling complete natural reductive dechlorination mechanisms of chlorinated ethenes in groundwater: Insights from functional gene analysis

Monitored natural attenuation (MNA) of chlorinated ethenes (CEs) has proven to be a cost-effective and environment-friendly approach for groundwater remediation. In this study, the complete dechlorination of CEs with formation of ethene under natural conditions, were observed at two CE-contaminated sites, including a pesticide manufacturing facility (PMF) and a fluorochemical plant (FCP), particularly in the deeply weathered bedrock aquifer at the FCP site. Additionally, a higher abundance of CE-degrading bacteria was identified with heightened dechlorination activities at the PMF site, compared to the FCP site. The reductive dehalogenase genes and Dhc 16 S rRNA gene were prevalent at both sites, even in groundwater where no CE dechlorination was observed. vcrA and bvcA was responsible for the complete dechlorination at the PMF and FCP site, respectively, indicating the distinct contributions of functional microbial species at each site. The correlation analyses suggested that Sediminibacterium has the potential to achieve the complete dechlorination at the FCP site. Moreover, the profiles of CE-degrading bacteria suggested that dechlorination occurred under Fe3+/sulfate-reducing and nitrate-reducing conditions at the PMF and FCP site, respectively. Overall these findings provided multi-lines of evidence on the diverse mechanisms of CE-dechlorination under natural conditions, which can provide valuable guidance for MNA strategies implementation.

Using Network Analysis and Predictive Functional Analysis to Explore the Fluorotelomer Biotransformation Potential of Soil Microbial Communities

Microbial transformation of per- and polyfluoroalkyl substances (PFAS), including fluorotelomer-derived PFAS, by native microbial communities in the environment has been widely documented. However, few studies have identified the key microorganisms and their roles during the PFAS biotransformation processes. This study was undertaken to gain more insight into the structure and function of soil microbial communities that are relevant to PFAS biotransformation. We collected 16S rRNA gene sequencing data from 8:2 fluorotelomer alcohol and 6:2 fluorotelomer sulfonate biotransformation studies conducted in soil microcosms under various redox conditions. Through co-occurrence network analysis, several genera, including Variovorax, Rhodococcus, and Cupriavidus, were found to likely play important roles in the biotransformation of fluorotelomers. Additionally, a metagenomic prediction approach (PICRUSt2) identified functional genes, including 6-oxocyclohex-1-ene-carbonyl-CoA hydrolase, cyclohexa-1,5-dienecarbonyl-CoA hydratase, and a fluoride-proton antiporter gene, that may be involved in defluorination. This study pioneers the application of these bioinformatics tools in the analysis of PFAS biotransformation-related sequencing data. Our findings serve as a foundational reference for investigating enzymatic mechanisms of microbial defluorination that may facilitate the development of efficient microbial consortia and/or pure microbial strains for PFAS biotransformation.

Evaluating groundwater ecosystem dynamics in response to post in-situ remediation of mixed chlorinated volatile organic compounds (CVOCs): An insight into microbial community resilience, adaptability, and metabolic functionality for sustainable remediation and ecosystem restoration

The in-situ remediation of groundwater contaminated with mixed chlorinated volatile organic compounds (CVOCs) has become a significant global research interest. However, limited attention has been given in understanding the effects of these remediation efforts on the groundwater microbial communities, which are vital for maintaining ecosystem health through their involvement in biogeochemical cycles. Hence, this study aimed to provide valuable insights into the impacts of in-situ remediation methods on groundwater microbial communities and ecosystem functionality, employing high-throughput sequencing coupled with functional and physiological assays. The results showed that both bioremediation and chemical remediation methods adversely affected microbial diversity and abundance compared to non-polluted sites. Certain taxa such as Pseudomonas, Acinetobacter, and Vogesella were sensitive to these remediation methods, while Aquabacterium exhibited greater adaptability. Functional annotation unveiled the beneficial impact of bioremediation on the sulfur cycle and specific taxa such as Cellvibrio, Massilia, Algoriphagus, and Flavobacterium which showed a significant positive relationship with dark oxidation of sulfur compounds. In contrast, chemical remediation showed adverse impacts on the nitrogen cycle with a reduced abundance of nitrogen and nitrate respiration along with a reduced utilization of amines (nitrogen rich substrate). The findings of this study offer valuable insights into the potential impacts of in-situ remediation methods on groundwater microbial communities and ecosystem functionality, emphasizing the need for meticulous consideration to ensure the implementation of effective and sustainable remediation strategies that safeguard ecosystem health and function.

Adaptation strategies and functional transitions of microbial community in pyrene-contaminated soils promoted by lead with Pseudomonas veronii and its extracellular polymeric substances

Pyrene was designated as a remediation target in this study, and low contamination of lead (Pb) was set to induce heavy metal stress. Pseudomonas veronii and its extracellular polymeric substances (EPSs) were chosen for biofortification, with the aim of elucidating the structural, metabolic, and functional responses of soil microbial communities. Community analysis of soil microorganisms using high-throughput sequencing showed that the co-addition of P. veronii and EPSs resulted in an increase in relative abundance of phyla associated with pyrene degradation, and formed a symbiotic system dominated by Firmicutes and Proteobacteria, which involved in pyrene metabolism. Co-occurrence network analysis revealed that the module containing P. veronii was the only one exhibiting a positive correlation between bacterial abundance and pyrene removal, indicating the potential of bioaugmentation in enriching functional taxa. Biofortification also enhanced the abundance of functional gene linked to EPS production (biofilm formation-Pseudomonas aeruginosa) and pyrene degradation. Furthermore, 17 potential functional bacteria were screened out using random forest algorithm. Lead contamination further promoted the growth of Proteobacteria, intensified cooperative associations among bacteria, and increased the abundance of bacteria with positive correlation with pyrene degradation. The results offer novel perspectives on alterations in microbial communities resulting from the synergistic impact of heavy metal stress and biofortification.

Synergistic binding mechanisms of co-contaminants in soil profiles: Influence of iron-bearing minerals and microbial communities

In contaminated soil sites, the coexistence of inorganic and organic contaminants poses a significant threat to both the surrounding ecosystem and public health. However, the migration characteristics of these co-contaminants within the soil and their interactions with key components, including Fe-bearing minerals, organic matter, and microorganisms, remain unclear. This study involved the collection of a 4.3-m-depth co-contaminated soil profile to investigate the vertical distribution patterns of co-contaminants (namely, arsenic, cadmium, and polychlorinated biphenyls (PCBs)) and their binding mechanisms with environmental factors. The results indicated a notable downward accumulation of inorganic contaminants with increasing soil depth, whereas PCBs were predominantly concentrated in the uppermost layer. Chemical extraction and synchrotron radiation analysis highlighted a positive correlation between the abundance of reactive iron (FeCBD) and both co-contaminants and microbial communities in the contaminated site. Furthermore, Mantel tests and structural equation modeling (SEM) demonstrated the direct impacts of FeCBD and microbial communities on co-contaminants within the soil profile. Overall, these results provided valuable insights into the migration and transformation characteristics of co-contaminants and their binding mechanisms mediated by minerals, organic matter, and microorganisms.

Dissolved organic compounds in shale gas extraction flowback water as principal disturbance factors of soil nitrogen dynamics

Flowback water, a by-product of shale gas extraction, represents an extremely complex industrial wastewater characterized by high organic compounds content and high salinity. The prospect of flowback water entering the soil through various approaches concerns regarding its ecological risk. Nitrogen mineralization (Nmin), a key rate-limiting step in the soil N cycle, might be adversely affected by flowback water. Nonetheless, no previous studies have examined the effects of flowback water on soil Nmin rates, let alone quantified the relative contributions of the major components of flowback water to changes in Nmin rates. Therefore, this study investigated the effects of flowback water and sterile flowback water at two different concentrations on the Nmin rates of three distinct soil types. This study aimed to elucidate the predominant influence of the key constituents within flowback water on the changes in soil Nmin rates. The results showed that soil soluble salt content, dissolved organic carbon (DOC) and dissolved nitrogen (DN) content significantly increased by 8.37 times, 9.5 % and 26.4 %, respectively, in soils contaminated by flowback water. In comparison with the control group, the introduction of flowback water resulted in a significant 25.9 % reduction in Nmin rate in sandy soils. Conversely, in clay and loam soils, there was a significant increase in Nmin rates by 44.9 % and 131.8 % respectively. Throughout the incubation period, leucine-aminopeptidase activity exhibited irregular fluctuations. Analysis of microbial communities demonstrated that flowback water only significant impacted soil rare microbial taxa, inducing a significant increase in alpha diversity for sandy, clay, and loamy soils by -16.9 %, 10.12 %, and 1.63 %, respectively. Linear regression and random forest analyses indicated that alterations in soil DOC:DN ratio and salt content were responsible for changes in soil Nmin rates within flowback water-contaminated soils. In contrast, only salt content significantly contributed to shifts in alpha diversity among soil rare microbial taxa. Structural equation modeling highlighted that the total effect of dissolved organic compounds (DOC and DN, λ = 0.64) from flowback water was greater than the total effect of salinity (λ = 0.24) on soil Nmin rates. In conclusion, our findings imply that dissolved organic compounds within flowback water play pivotal roles in determining soil Nmin rates. To the best of our knowledge, this is the first study to reveal the effects of major components in the flowback water on soil N mineralization rates.

Improve Niche Colonization and Microbial Interactions for Organohalide-Respiring-Bacteria-Mediated Remediation of Chloroethene-Contaminated Sites

Organohalide-respiring bacteria (OHRB)-mediated reductive dehalogenation is promising in in situ bioremediation of chloroethene-contaminated sites. The bioremediation efficiency of this approach is largely determined by the successful colonization of fastidious OHRB, which is highly dependent on the presence of proper growth niches and microbial interactions. In this study, based on two ecological principles (i.e., Priority Effects and Coexistence Theory), three strategies were developed to enhance niche colonization of OHRB, which were tested both in laboratory experiments and field applications: (i) preinoculation of a niche-preparing culture (NPC, being mainly constituted of fermenting bacteria and methanogens); (ii) staggered fermentation; and (iii) increased inoculation of CE40 (a Dehalococcoides-containing tetrachloroethene-to-ethene dechlorinating enrichment culture). Batch experimental results show significantly higher dechlorination efficiencies, as well as lower concentrations of volatile fatty acids (VFAs) and methane, in experimental sets with staggered fermentation and niche-preconditioning with NPC for 4 days (CE40_NPC-4) relative to control sets. Accordingly, a comparatively higher abundance of Dehalococcoides as major OHRB, together with a lower abundance of fermenting bacteria and methanogens, was observed in CE40_NPC-4 with staggered fermentation, which indicated the balanced syntrophic and competitive interactions between OHRB and other populations for the efficient dechlorination. Further experiments with microbial source tracking analyses suggested enhanced colonization of OHRB by increasing the inoculation ratio of CE40. The optimized conditions for enhanced colonization of OHRB were successfully employed for field bioremediation of trichloroethene (TCE, 0.3-1.4 mM)- and vinyl chloride (VC, ∼0.04 mM)-contaminated sites, resulting in 96.6% TCE and 99.7% VC dechlorination to ethene within 5 and 3 months, respectively. This study provides ecological principles-guided strategies for efficient bioremediation of chloroethene-contaminated sites, which may be also employed for removal of other emerging organohalide pollutants.

Oilomics: An important branch of foodomics dealing with oil science and technology

Oil is one of three nutritious elements. The application of omics techniques in the field of oil science and technology is attracted increasing attention. Oilomics, which emerged as an important branch of foodomics, has been widely used in various aspects of oil science and technology. However, there are currently no articles systematically reviewing the application of oilomics. This paper aims to provide a critical overview of the advantages and value of oilomics technology compared to traditional techniques in various aspects of oil science and technology, including oil nutrition, oil processing, oil quality, safety, and traceability. Moreover, this article intends to review major issues in oilomics and give a comprehensive, critical overview of the current state of the art, future challenges and trends in oilomics, with a view to promoting the optimal application and development of oilomics technology in oil science and technology.

Deep soil microbial carbon metabolic function is important but often neglected: a study on the Songnen Plain reed wetland, Northeast China

Soil microbial carbon metabolism is critical in wetland soil carbon cycling, and is also a research hotspot at present. However, most studies focus on the surface soil layer in the wetlands and the microorganisms associated with this layer. In this study, 0-75 cm soil profiles were collected from five widely separated reed wetlands in the Songnen Plain, which has a large number of middle-high latitude inland saline-sodic wetlands. The Biolog-ECO method was used to determine the carbon metabolic activity and functional diversity of soil microorganisms. The results showed that soil carbon metabolic activity decreased with increasing soil depth. The carbon metabolic activity of soil microorganisms in the 60-75 cm layer was approximately 57.41%-74.60% of that in the 0-15 cm layer. The soil microbial Shannon index and utilization rate of amines decreased with an increase in soil depth, while the Evenness index and utilization rate of polymers tended to increase with soil depth. Dissolved organic carbon (DOC) is the most important factor affecting microbial carbon source utilization preference, because microorganisms mainly obtain the carbon source from DOC. The result of the correlation analysis showed that the soil microbial carbon metabolic activity, Shannon index, and Evenness index significantly correlated with soil total carbon (TC), microbial biomass carbon (MBC), DOC, total nitrogen (TN), ammonium nitrogen (NH4 +-N), nitrate nitrogen (NO3 --N) contents, and electrical conductivity (EC). This study emphasized the important role of microbial carbon metabolic function in deep soil.

Soil organic matter and nutrient availability affect the applicability of low-carbon energy source in Dehalococcoides-augmented soil

Dehalococcoides is a functional microorganism that completely dechlorinates trichloroethene (TCE). Augmentation with pure Dehalococcoides is important for reducing environmental disturbances that accompany bioaugmentation. However, the applicability of Dehalococcoides-bioaugmentation to contaminated soils is unclear. In this study, seven low-carbon energy sources (methanol, formate, acetate, ethanol, lactate, citrate, and benzoate) were used as electron donors for Dehalococcides to evaluate its applicability in remediating TCE-contaminated soils. Soil microcosms supplemented with ethanol, formate, or lactate showed relatively high dechlorination activity within 111-180 days. The functional gene profiles predicted by PICRUSt2 from 16 S rRNA gene sequences were similar in the proportions of dehydrogenases, which initiate electron donor oxidation, in all soils and did not seem to reflect Dehalococcoides-bioaugmentation applicability. Soils with higher organic matter content (>3.2%; dry weight base) and protein concentration (>1.6 µg/mL) supported complete dechlorination. These results suggest that organic matter and nutrient availability mainly affect successful TCE dechlorination in Dehalococcoides-augmented soils. The study offers significant experimental support for comprehending the suitability of low-carbon energy sources in successful bioaugmentation, aiming to mitigate environmental disturbances associated with the process.

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

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

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.

Identification and synergetic mechanism of TCE, H2 and O2 metabolic microorganisms in the joint H2/O2 system

The sole H₂ and O₂ usually promote chlorinated hydrocarbons (CHCs) biotransformation by several mechanisms, including reductive dechlorination and aerobic oxidation. However, the mechanism of the CHCs transformation in joint H₂ and O₂ system (H₂/O₂ system) is still unclear. In this study, the degradation kinetics of trichloroethene (TCE) were investigated and DNA stable isotope probing (DNA-SIP) were used to explore the synergistic mechanism of functional microorganisms on TCE degradation under the condition of H₂/O₂ coexistence. In the H₂/O₂ microcosm, TCE was significantly removed by 13.00 μM within 40 days, much higher than N₂, H₂ and O₂ microcosms, and 1,1-DCE was detected as an intermediate. DNA-SIP technology identified three anaerobic TCE metabolizers, five aerobic TCE metabolizers, nine hydrogen-oxidizing bacteria (HOB), some TCE metabolizers utilizing limited O₂, and some anaerobic dechlorinating bacteria reductively using H₂ to dechlorinate TCE. It is also confirmed for the first time that 3 OUTs belonging to Methyloversatilis and SH-PL14 can simultaneously utilize H₂ and O₂ as energy sources to grow and metabolize TCE or 1,1-DCE. HOB may provide carbon sources or electron acceptors or donors for TCE biotransformation. These findings confirm the coexistence of anaerobic and aerobic TCE metabolizers and degraders, which synergistically promoted the conversion of TCE in the joint H₂/O₂ system. Our results provide more information about the functional microbe resources and synergetic mechanisms for TCE degradation.

Copper-oxide nanoparticles exert persistent changes in the structural and functional microbial diversity: A 60-day mesocosm study of zinc-oxide and copper-oxide nanoparticles in the soil-microorganism-nanoparticle system

Recent advances in nanotechnology and development of nanoformulation methods, has enabled the emergence of precision farming - a novel farming method that involves nanopesticides and nanoferilizers. Zinc-oxide nanoparticles serve as a Zn source for plants, but they are also used as nanocarriers for other agents, whereas copper-oxide nanoparticles possess antifungal activity, but in some cases may also serve as a micronutrient providing Cu ions. Excessive application of metal-containing agents leads to their accumulation in soil, where they pose a threat to non-target soil organisms. In this study, soils obtained from the environment were amended with commercial zinc-oxide nanoparticles: Zn-O_xNPs_(10-30), and newly-synthesized copper-oxide nanoparticles: Cu-O_xNPs_(1-10). Nanoparticles (NPs) in 100 and 1000 mg kg^-1 concentrations were added in separate set-ups, representing a soil-microorganism-nanoparticle system in a 60-day laboratory mesocosm experiment. To track environmental footprint of NPs on soil microorganisms, a Phospholipd Fatty Acid biomarker analysis was employed to study microbial community structure, whereas Community-Level Physiological Profiles of bacterial and fungal fractions were measured with Biolog Eco and FF microplates, respectively. The results revealed a prominent and persistent effects exerted by copper-containing nanoparticles on non-target microbial communities. A severe loss of Gram-positive bacteria was observed in conjunction with disturbances in bacterial and fungal CLPPs. These effects persisted till the end of a 60-day experiment, demonstrating detrimental rearrangements in microbial community structure and functions. The effects imposed by zinc-oxide NPs were less pronounced. As persistent changes were observed for newly synthesized Cu-containing NPs, this work stresses the need for obligatory testing of nanoparticle interactions with non-target microbial communities in long-term experiments, especially during the approval procedures of novel nano-substances. It also underlines the role of in-depth physical and chemical studies of NP-containing agents, which may be tweaked to mitigate the unwanted behavior of such substances in the environment and preselect their beneficial characteristics.

Effects of copper sulfate algaecide on the cell growth, physiological characteristics, the metabolic activity of Microcystis aeruginosa and raw water application

Harmful cyanobacteria blooms (HCBs) occurred frequently and become a serious scientific challenge. Copper sulfate (CuSO₄) is a broad-spectrum chemical algaecide to control algae blooms. Herein, the Microcystis aeruginosa was exposed to different CuSO₄ (0.0, 0.2 and 0.5 mg/L) to assess the variations in algal physiological process and metabolic profiles. The results indicated that exposure to CuSO₄ of 0.5 mg/L at 72 h could significantly inhibit the cell growth and photosynthetic capacity of M. aeruginosa, including chl-a content and chlorophyll fluorescence parameters. Plasma membrane damage causing cell lysis of M. aeruginosa increased the K⁺ release. The increase of SOD and CAT suggested that CuSO₄ treatment caused oxidative stress in algal cells. Different doses of CuSO₄ modified the carbon metabolic potential, algal cells had their unique metabolic mode thereby. Moreover, the research further verified that CuSO₄ would also inhibit algal growth and change algal community structure in site-collected water application. Overall, laboratory results of M. aeruginosa to CuSO₄ and site-collected water application of algal responses to CuSO₄ might be conducive to uncovering the controlling mechanism of algae and the potential effect of carbon cycling in an ecological environment.

Depth-dependent patterns of soil microbial community in the E-waste dismantling area

The long-term dismantling of electronic waste (E-waste) has contaminated the soil environment considerably. In spite of this, it is unknown if it affects the depth-resolved microbial communities. In the present research, six soil profiles (dismantling sites and the surrounding farmland) were collected from one of the largest Chinese E-waste disposal centers to identify depth-resolved microbiota and assess how heavy metal contamination affects microbial adaptation. Results suggested that cadmium (0.12-7.22 mg kg^-1) and copper (18.99-11282.03 mg kg^-1) were the main pollutants in the test soil profiles, and their concentrations gradually decreased with depth. The surrounding contaminated farmland has a more complex interaction and higher modularity (0.77-0.85) among microbes, indicating a stronger niche differentiation to enhance functional diversity. The proportion of positive interactions between taxa decreased with depth, as high heavy metals contamination in the topsoil results in the co-occurrence of microorganisms with the same ecological niche that collaborated to face environmental stress. Soil physicochemical properties, heavy metals concentration, and soil depth critically affect microbial communities. Microbial community assembly processes in the topsoil were affected by environmental filtering, i.e., by deterministic processes (NST: 13-52%), while were more stochastic (NST: 46-72%) in the subsoil due to the environment of soil becoming more homogeneous as soil depth increased.

The ecological response and distribution characteristics of microorganisms and polycyclic aromatic hydrocarbons in a retired coal gas plant post-thermal remediation site

Thermal remediation is one of the most common approaches of removing organic pollutants in the retired contamination sites. However, little is known about the performance of bacterial community characteristics after in situ thermal remediation. In this study, the ecological response and spatial distributional characteristics of microorganisms and polycyclic aromatic hydrocarbons (PAHs) were investigated using a high throughput sequencing method in a retired coal gas plant site after in situ thermal remediation in Nanjing, China. Combination of Venn, clustering-correlation heatmap and two - factor correlation network analysis revealed that, microbial communities were obviously affected and classified by soil depths, temperature, and contamination level, respectively. The common and endemic microorganisms of each group were identified. The relative abundances of Thermaerobacter, Calditerricola, Brevibacillus, Ralstonia and Rhodococcus (aerobic bacteria) gradually declined with the increase of soil depth, while those of Bacillus, Fictibacillus, Paenibacillus, Rheinheimera presented opposite tendency. Some thermophilic degradation bacteria of PAHs, including Thermaerobacter, Calditerricola, Bacillus, Rhodococcus, unclassified_p__Firmicutes, Arthrobacter and Deinococcus, were identified and increased in the abundance at heavily polluted sites. Additionally, Proteobacteria, Bacteroidota, Deinococcota, Chloroflexi, Acidobacteriota, and Actinobacteriota showed negative response to the increase of soil depth, temperature and pollution level, while Firmicutes presented a positive response. This implied that Firmicutes has better stress resistance and adaptability to thermal remediation condition. The key environmental factors affecting microorganism composition and distribution were Temperature, Total nitrogen, Oxidation-Reduction Potential, Organic matters, and PAHs concentrations, which explains the dominant driving mechanism of soil depth, temperature, and contamination level on microbial characteristics in thermal remediation site. Our study could contribute to a better understanding of the resilience and adaptation mechanisms of microbial community at the contaminated site after the in situ thermal remediation.

Analysis and interpretation of hot springs water, biofilms, and sediment bacterial community profiling and their metabolic potential in the area of Taiwan geothermal ecosystem

Microorganisms developed a mechanism that copes with heat, acidity, and high dissolved metal concentrations that likely first evolved. The geothermal fluids emerging in the geothermal springs of Taiwan, located at a subduction zone, are still under signs of progress in the characterization of the various microbial taxonomic changes over time. However, no systematic studies have been performed to compare water, biofilms, and sediment bacterial communities and the primary driving force of dissolved and mineral substrates capable of supporting microbial metabolism. In this study, 16S rRNA gene sequencing was employed for bacterial community exploration, and their potential metabolic pathways involved from water, biofilms, and sediment samples, collected from the geothermal valley (Ti-re-ku). Metagenomic data revealed that the water samples had higher bacterial diversity and richness than biofilms and sediment samples. At the genus level, Alicyclobacillus, Thiomonas, Acidocella, Metallibacterium, Picrophilus, and Legionella were significantly abundant in the water samples. The biofilms were rich in Aciditerrimonas, Bacillus, Acidithiobacillus, and Lysinibacillus, whereas the sediment samples were abundant in Sulfobacillus. The PICRUSt2-predicted functional results revealed that heavy metal-related functions such as heavy-metal exporter system, cobalt‑zinc‑cadmium resistance, arsenical pump, high-affinity nickel-transport, and copper resistance metabolisms were significant in the water samples. Moreover, sulfur-related pathways such as thiosulfate oxidation, dissimilatory sulfate reduction, and assimilatory sulfate reduction were important in water samples, followed by biofilms and sediment. Therefore, our findings highlighted the comparative taxonomic diversity and functional composition contributions to geothermal fluid, with implications for understanding the evolution and ecological niche dimension of microbes which are the key to geothermal ecosystem function.

Insights into remediation effects and bacterial diversity of different remediation measures in rare earth mine soil with SO4 2- and heavy metals

The increased demand for rare earth resources has led to an increase in the development of rare earth mines (REMs). However, the production of high-concentration leaching agents (SO₄ ^2-) and heavy metals as a result of rare earth mining has increased, necessitating the removal of contaminants. Here, a series of experiments with different remediation measures, including control (CK), sulfate-reducing bacteria (SRB) alone (M), chemicals (Ca(OH)₂, 1.5 g/kg) plus SRB (CM-L), chemicals (Ca(OH)₂, 3.0 g/kg) plus SRB (CM-M), and chemicals (Ca(OH)₂, 4.5 g/kg) plus SRB (CM-H), were conducted to investigate the removal effect of SO₄ ^2-, Pb, Zn, and Mn from the REM soil. Then, a high-throughput sequencing technology was applied to explore the response of bacterial community diversity and functions with different remediation measures. The results indicated that CM-M treatment had a more efficient removal effect for SO₄ ^2-, Pb, Zn, and Mn than the others, up to 94.6, 88.3, 98.7, and 91%, respectively. Soil bacterial abundance and diversity were significantly affected by treatments with the inoculation of SRB in comparison with CK. The relative abundance of Desulfobacterota with the ability to transform SO₄ ^2- into S^2- increased significantly in all treatments, except for CK. There was a strong correlation between environmental factors (pH, Eh, SO₄ ^2-, Pb, and Zn) and bacterial community structure. Furthermore, functional prediction analysis revealed that the SRB inoculation treatments significantly increased the abundance of sulfate respiration, sulfite respiration, and nitrogen fixation, while decreasing the abundance of manganese oxidation, dark hydrogen oxidation, and denitrification. This provides good evidence for us to understand the difference in removal efficiency, bacterial community structure, and function by different remediation measures that help select a more efficient and sustainable method to remediate contaminants in the REM soil.

Systematic assessment of mineral distribution and diversity of microbial communities and its interactions in the Taiwan subduction zone of mud volcanoes

Mud volcanoes are the most dynamic and unstable sedimentary structures in the areas of tectonic compression like the subduction zones. In this study, we comprehensively analyzed the distribution of minerals as well as diversity, abundance and metabolic potential of the microbial communities of major mud volcanic groups across Taiwan namely Chu-kou Fault (CKF), Gu-ting-keng Anticline (GTKA), Chi-shan Fault (CSF), and Longitudinal Valley Fault (LVF). The mud volcano fluids recorded relatively higher Na and Cl contents than the other elements, particularly in the CKF and GTKA groups. The highest microbial diversity and richness were observed in the CSF group, followed by the GTKA group, whereas the lowest microbial diversity was observed in the CKF and LVF groups. Proteobacteria were common in all the sampling sites, except WST-7 and WST-H (Wu-Shan-Ting) of the CSF group, which were abundant in Chloroflexi. The halophilic genus Alterococcus was abundant in the Na-and Cl-rich CL-A sites of the CKF group. Sulfurovum was dominant in the CLHS (Chung-Lun hot spring) site of the CKF group and was positively correlated with sulfur/thiosulfate respiration, which might have resulted in a higher expression of these pathways in the respective group. Aerobic methane-oxidizing microbial communities, such as Methylobacter, Methylomicrobium, Methylomonas, and Methylosoma, constituted a dominant part of the LVF and CSF groups, except for the YNH-A and YNH-B (Yang-Nyu-Hu) sites. The WST-7 and JS sites were abundant in both methane-producing and methane-oxidizing microbial communities. The LGH-F1 (Lei-Gong-Huo) site was dominated by both methanotrophic and methylotrophic genera, such as Methylomicrobium and Methylophaga, respectively. Methylotrophy, methanotrophs, and hydrocarbon-degrading pathways were more abundant in the LVF and CSF groups but not in the remaining groups. The results of this study extend our knowledge of the diversity, abundance, and metabolic functions of prokaryotes in major terrestrial mud volcanoes in Taiwan.

Unravelling the ultramafic rock-driven serpentine soil formation leading to the geo-accumulation of heavy metals: An impact on the resident microbiome, biogeochemical cycling and acclimatized eco-physiological profiles

In the present study, we have underpinned the serpentine rock, serpentinized ultramafic soil and rhizosphere's microbial communities, signifying their heavy metals-exposed taxa signatures and functional repertoires in comparison to non-serpentine soils. The results revealed that the serpentine rock embedded soil highlighted the geo-accumulation of higher amount of Cr and Ni impacting soil microbial diversity negatively by metal stress-driven selection. Biolog Ecoplate CLPP defined a restricted spectrum of C-utilization in the higher heavy metal-containing serpentine samples compared to non-serpentine. The linear discriminant analysis (LDA) score identified a higher abundance of Desulfobacterota, Opitutales, and Bacteroidales in low Cr and Ni-stressed non-serpentine-exposed samples. Whereas the abundance of Propionibacteriales and Actinobacteriota were significantly enriched in the serpentine niche. Further, the C, N, S, Fe, and methane biogeochemical cycles linked functional members were identified, and showing higher functional diversity in low Cr and Ni concentration-containing rhizosphere JS-soils. The Pearson correlation coefficient (r) value confirmed the abundance of functional members linked to specific biogeochemical cycle, positively correlated with relevant pathway enrichment. Ultimately, this study highlighted the heavy metal stress within a serpentine setting that could limit the resident microbial community's metabolic diversity and further select the bacteria that could thrive in the serpentine-associated heavy metal-stressed soils. These acclimatized microbes could pave the way for the future applications in the soil conservation and management.

Recent advances and trends of trichloroethylene biodegradation: A critical review

Trichloroethylene (TCE) is a ubiquitous chlorinated aliphatic hydrocarbon (CAH) in the environment, which is a Group 1 carcinogen with negative impacts on human health and ecosystems. Based on a series of recent advances, the environmental behavior and biodegradation process on TCE biodegradation need to be reviewed systematically. Four main biodegradation processes leading to TCE biodegradation by isolated bacteria and mixed cultures are anaerobic reductive dechlorination, anaerobic cometabolic reductive dichlorination, aerobic co-metabolism, and aerobic direct oxidation. More attention has been paid to the aerobic co-metabolism of TCE. Laboratory and field studies have demonstrated that bacterial isolates or mixed cultures containing Dehalococcoides or Dehalogenimonas can catalyze reductive dechlorination of TCE to ethene. The mechanisms, pathways, and enzymes of TCE biodegradation were reviewed, and the factors affecting the biodegradation process were discussed. Besides, the research progress on material-mediated enhanced biodegradation technologies of TCE through the combination of zero-valent iron (ZVI) or biochar with microorganisms was introduced. Furthermore, we reviewed the current research on TCE biodegradation in field applications, and finally provided the development prospects of TCE biodegradation based on the existing challenges. We hope that this review will provide guidance and specific recommendations for future studies on CAHs biodegradation in laboratory and field applications.

Exploration of pristine plate-tectonic plains and mining exposure areas for indigenous microbial communities and its impact on the mineral-microbial geochemical weathering process in ultramafic setting

Heavy metal release from harsh ultramafic settings influences microbial diversity and function in soil ecology. This study aimed to determine how serpentine mineralosphere bacterial assemblies and their functions differed in two different plate-tectonic plains and mining exposure sites under heavy metal release conditions. The results showed that the Proteobacteria, Actinobacteria, Cyanobacteria, Planctomycetes, and Chloroflexi were the most abundant bacterial groups among all the sites. The log10-based LDA scores highlighted that some specific groups of bacterial assemblies were enriched in plate-tectonic plains and mining activity areas of the serpentine mineralosphere. Functional prediction revealed that the abundance of heavy metal (Cr and Ni) resistance and biogeochemical cycles involving functional KEGG orthology varied in samples from plate-tectonic plains and mining activity sites. The bipartite plot showed that the enrichment of the biogeochemical cycle and heavy metal resistance functional genes correlated with the abundance of serpentine mineralosphere bacterial groups at a 0.005% confidence level. The co-occurrence network plot revealed that the interconnection pattern of the indigenous bacterial assemblies changed in different plate-tectonic plains and mining exposure areas. Finally, this study concluded that due to heavy metal release, the variation in bacterial assemblies, their functioning, and intercommunity co-occurrence patterns were clarified the synergetic effect of mineral-microbial geochemical weathering process in serpentine mining areas.

Functional interplay between antagonistic bacteria and Rhizoctonia solani in the tomato plant rhizosphere

Microbial interactions with plant roots play an imperial role in tomato plant growth and defense against the Rhizoctonia solani. This study performed a field experiment with two antagonistic bacteria (Pseudomonas and Bacillus) inoculated in healthy and Rhizoctonia solani treated soil in tomato rhizosphere to understand the metabolic pattern and microbial function during plant disease suppression. In the present study, we assessed soil and microbial enzymes, bacterial and fungal cell forming unit (CFU), and carbon utilization profiling through Bio-Eco plates of rhizoplane samples. Antagonist bacteria and pathogen interaction significantly (p < 0.05) influenced the bacterial count, soil enzymes (chitinase and glucanase), and bacterial function (siderophore and chitinase production). These results indicated that these variables had an imperial role in disease suppression during plant development. Furthermore, the metabolic profiling showed that carbon source utilization enhanced under fruit development and ripening stages. These results suggested that carbon sources were essential in plant/pathogen/antagonist interaction. Substrates like β-methyl-D-glucoside, D-mannitol, D-galacturonic acid, N-acetyl-D-glucosamine, and phenylethylamine strongly connect with the suppuration of root rot disease. These carbon sources may help to propagate a healthy microbial community to reduce the pathogen invasion in the plant root system, and these carbon sources can be stimulators of antagonists against pathogens in the future.

Effects of pyrene on the structure and metabolic function of soil microbial communities

The widely detected pyrene (PYR) is prone to accumulate and pose risks to the soil ecosystem. In this study, an aerobic closed microcosm was constructed to assess the effects of PYR at the environmental concentration (12.09 mg kg^-1) on the structure, interactions, and metabolism of carbon sources of soil microbial communities. The results found that half-life of PYR was 37 d and its aerobic biodegradation was mainly implemented by both Gram-negative and Gram-positive bacteria as revealed by the quantitative results. High-throughput sequencing based on 16 S rRNA and ITS genes showed that PYR exposure interfered more significantly with the diversity and abundance of the bacterial community than that of the fungal community. For bacteria, rare species were sensitive to PYR, while Gemmatimonadota, Gaiellales, and Planococcaceae involved in organic pollutants detoxification and degradation were tolerant of PYR stress. Co-occurrence network analysis demonstrated that PYR enhanced the intraspecific cooperation within the bacterial community and altered the patterns of trophic interaction in the fungal community. Furthermore, the keystone taxa and their topological roles were altered, potentially inducing functionality changes. Function annotation suggested PYR inhibited the nitrogen fixation and ammonia oxidation processes but stimulated methylotrophy and methanol oxidation, especially on day 7. For the metabolism, microbial communities accelerated the metabolism of nitrogenous carbon sources (e.g. amine) to meet the physiological needs under PYR stress. This study clarifies the impacts of PYR on the structure, metabolism, and potential N and C cycling functions of soil microbial communities, deepening the knowledge of the environmental risks of PYR.

The Impact of Swine Manure Biochar on the Physical Properties and Microbial Activity of Loamy Soils

Biochar has been proven to influence soil hydro-physical properties, as well as the abundance and diversity of microbial communities. However, the relationship between the hydro-physical properties of soils and the diversity of microbial communities is not well studied in the context of biochar application. The soil analyzed in this study was collected from an ongoing field experiment (2019–2024) with six treatments and three replications each of biochar (B1 = 25 t·ha⁻¹ and B0 = no biochar) and nitrogen fertilizer (N1 = 160, N2 = 120 kg·ha⁻¹, and N0 = no fertilizer). The results show that biochar treatments (B1N0, B1N1, and B1N2) significantly improved the soil bulk density and total soil porosity at different depths. The B1N1 treatment substantially enhanced the volumetric water content (VMC) by 5–7% at −4 to −100 hPa suction at 5–10 cm depth. All three biochar treatments strengthened macropores by 33%, 37%, and 41%, respectively, at 5–10 cm depth and by 40%, 45%, and 54%, respectively, at 15–20 cm depth. However, biochar application significantly lowered hydraulic conductivity (HC) and enhanced carbon source utilization and soil indices at different hours. Additionally, a positive correlation was recorded among carbon sources, indices, and soil hydro-physical properties under biochar applications. We can summarize that biochar has the potential to improve soil hydro-physical properties and soil carbon source utilization; these changes tend to elevate fertility and the sustainability of Cambisol.

Comparison of bacterial communities and their functional profiling using 16S rRNA gene sequencing between the inherent serpentine-associated sites, hyper-accumulator, downgradient agricultural farmlands, and distal non-serpentine soils

This study aims to determine and compare the bacterial community and functional profiles associated with serpentine sites, innate hyper-accumulating weed, downgradient agricultural farmlands and non-serpentine sites using 16S rRNA gene sequencing. Elemental analysis revealed that the serpentine rock and weathered soil have higher magnesium, nickel, chromium, magnesium/calcium and lower calcium/magnesium ratios and agricultural farmlands have recorded elevated chromium. Proteobacteria were found predominant, except the non-serpentine site which was rich in Cyanobacteria. PCA analysis at the genus level indicates the uniqueness of different experimental groups, except the hyperaccumulators which exhibited relatively less dissimilarity. The shift analysis showed the serpentine sites were characterized by the abundance of bacteria having heavy metal effluxion. The hyper-accumulating weeds were higher in plant growth-promoting bacteria expressing tolerance against heavy metals toxicity such as nickel, chromium, cobalt and arsenic. Besides, the agricultural lands were abundant in wetland-associated methanogens and metal (manganese, iron and zinc) transporting function related bacteria. The results suggest that the inherent edaphic factors including heavy metal content, the interacting behavior of hyperaccumulator's rhizosphere microbiota with soil and anthropogenic activities such as agricultural practices could be a major determinant of the variation in the bacterial community selection and abundance in the respective study sites.

Effect of In Situ Bioremediation of Soil Contaminated with DDT and DDE by Stenotrophomonas sp. Strain DXZ9 and Ryegrass on Soil Microorganism

In the present study, the changes in the microbial populations, enzyme activity and bacterial community structure in contaminated soils were investigated during the bioremediation of using Stenotrophomonas sp. strain DXZ9 and ryegrass. The results showed that the removal rates were 81% for DDT and 55% for DDE (69% for DDTs) with ryegrass-microbe. Microbial activity was remarkably improved, and the number of bacteria increased sharply from 7.32 × 106 to 2.56 × 108 cells/g in the 10 days due to successful colonization of the strains and effects of the ryegrass rhizosphere. There was significant difference in fungi number with ryegrass when comparing the 30th and 90th days with the 210th day: The actinomycete number in the soil with ryegrass was higher than without ryegrass, and it indicated that the number of microorganisms significantly increased under the action of ryegrass. The activities of polyphenol oxidase, dehydrogenase and catalase were significantly activated by the combination of ryegrass and microbe, and urease activity was less affected: It has influence on the diversity of bacterial community structure in the soil, but its influence gradually decreased by denaturing gradient gel electrophoresis with an extension in time. The activities represented promising tools for decontaminating and restoring the ecosystem in sustainable ways, and proposing new approaches and technological bottlenecks to promote DDT biodegradation is very significant.

Assessment of Temporal Effects of a Mud Volcanic Eruption on the Bacterial Community and Their Predicted Metabolic Functions in the Mud Volcanic Sites of Niaosong, Southern Taiwan

The microbial communities inhabiting mud volcanoes have received more attention due to their noteworthy impact on the global methane cycle. However, the impact of temporal effects of volcanic eruptions on the microbial community’s diversity and functions remain poorly characterized. This study aimed to underpin the temporal variations in the bacterial community’s diversity and PICRUSt-predicted functional profile changes of mud volcanic sites located in southern Taiwan using 16S rRNA gene sequencing. The physicochemical analysis showed that the samples were slightly alkaline and had elevated levels of Na⁺, Cl⁻, and SO₄²⁻. Comparatively, the major and trace element contents were distinctly higher, and tended to be increased in the long-period samples. Alpha diversity metrics revealed that the bacterial diversity and abundance were lesser in the initial period, but increased over time. Instead, day 96 and 418 samples showed reduced bacterial abundance, which may have been due to the dry spell that occurred before each sampling. The initial-period samples were significantly abundant in haloalkaliphilic marine-inhabiting, hydrocarbon-degrading bacterial genera such as Marinobacter, Halomonas, Marinobacterium, and Oceanimonas. Sulfur-reducing bacteria such as Desulfurispirillum and Desulfofarcimen were found dominant in the mid-period samples, whereas the methanogenic archaeon Methanosarcina was abundant in the long-period samples. Unfortunately, heavy precipitation encountered during the mid and long periods may have polluted the volcanic site with animal pathogens such as Desulfofarcimen and Erysipelothrix. The functional prediction results showed that lipid biosynthesis and ubiquinol pathways were significantly abundant in the initial days, and the super pathway of glucose and xylose degradation was rich in the long-period samples. The findings of this study highlighted that the temporal effects of a mud volcanic eruption highly influenced the bacterial diversity, abundance, and functional profiles in our study site.