Fertilized agroecosystems may show considerable leaching of the mobile nitrogen (N) compound NO3−, which pollutes groundwater and causes eutrophication of downstream waterbodies. Riparian buffer ...zones, positioned between terrestrial and aquatic environments, effectively remove NO3− and serve as a hotspot for N2O emissions. However, microbial processes governing NO3− reduction in riparian zones still remain largely unclear. This study explored the underlying mechanisms of various N-loss processes in riparian soil horizons using isotopic tracing techniques, molecular assays, and high-throughput sequencing. Both anaerobic ammonium oxidation (anammox) and denitrification activity were maximized in the riparian fringe rather than in the central zones. Denitrifying anaerobic methane oxidation (damo) process was not detected. Interestingly, both contrasting microbial habitats were separated by a groundwater table, which forms an important biogeochemical interface. Denitrification dominated cumulative N-losses in the upper unsaturated soil, while anammox dominated the lower oxic saturated soil horizons. Archaeal and bacterial ammonium oxidation that couple dissimilatory nitrate reduction to ammonium (DNRA) with a high cell-specific rate promoted anammox even further in oxic subsurface horizons. High-throughput sequencing and network analysis showed that the anammox rate positively correlated with Candidatus ‘Kuenenia’ (4%), rather than with the dominant Candidatus ‘Brocadia’. The contribution to N-loss via anammox increased significantly with the water level, which was accompanied by a significant reduction of N2O emission (∼39.3 ± 10.6%) since N-loss by anammox does not cause N2O emissions. Hence, water table management in riparian ecotones can be optimized to reduce NO3− pollution by shifting from denitrification to the environmentally friendly anammox pathway to mitigate greenhouse gas emissions.
Display omitted
•Horizontally anammox and denitrification rate maximized in riparian fringe zones.•Denitrification and anammox separately dominate N-loss in upper unsaturated and lower saturated soil horizons.•Anammox contribution increased with water-level rising accompanied with N2O reduction.•Optimizing water-table management can reduce NO3− moreover mitigating N2O emission.•Ammonium oxidation coupling DNRA promote anammox in riparian zones.
Polybrominated diphenyl ethers (PBDEs), commonly used as flame retardants in a wide variety of consumer products, are emerging persistent pollutants and ubiquitously distributed in the environment. ...The lack of proper bacterial populations to detoxify these recalcitrant pollutants, in particular of higher brominated congeners, has confounded the attempts to bioremediate PBDE-contaminated sites. In this study, we report a
-containing enrichment culture, PB, which completely debrominates 0.44 μM tetra-brominated diphenyl ether (BDE) 47 to diphenyl ether within 25 days (0.07 μM Br
/day) and extensively debrominates 62.4 ± 4.5% of 0.34 μM hepta-BDE 183 (0.006 μM Br
/day) with a predominant generation of penta- through tri-BDEs as well as small amounts of diphenyl ether within 120 days. Later, a marked acceleration rate (0.021 μM Br
/day) and more extensive debromination (87.7 ± 2.1%) of 0.38 μM hepta-BDE 183 was observed in the presence of 0.44 μM tetra-BDE 47, which is achieved
the faster growth rate of responsible bacterial populations on lower BDE-47 and debromination by expressed BDE-47 reductive dehalogenases. Therefore, the PB enrichment culture can serve as a potential candidate for
PBDE bioremediation since both BDE-47 and BDE-183 are dominant and representative BDE congeners and often coexist in contaminated sites.
Fastidious anaerobic bacteria play critical roles in environmental bioremediation of halogenated compounds. However, their characterization and application have been largely impeded by difficulties ...in growing them in pure culture. Thus far, no pure culture has been reported to respire on the notorious polychlorinated biphenyls (PCBs), and functional genes responsible for PCB detoxification remain unknown due to the extremely slow growth of PCB-respiring bacteria. Here we report the successful isolation and characterization of three Dehalococcoides mccartyi strains that respire on commercial PCBs. Using high-throughput metagenomic analysis, combined with traditional culture techniques, tetrachloroethene (PCE) was identified as a feasible alternative to PCBs to isolate PCB-respiring Dehalococcoides from PCB-enriched cultures. With PCE as an alternative electron acceptor, the PCBrespiring Dehalococcoides were boosted to a higher cell density (1.2 × 10⁸ to 1.3 × 10⁸ cells per mL on PCE vs. 5.9 × 10⁻ to 10.4 × 10⁻ cells per mL on PCBs) with a shorter culturing time (30 d on PCE vs. 150 d on PCBs). The transcriptomic profiles illustrated that the distinct PCB dechlorination profile of each strain was predominantly mediated by a single, novel reductive dehalogenase (RDase) catalyzing chlorine removal from both PCBs and PCE. The transcription levels of PCB-RDase genes are 5-60 times higher than the genome-wide average. The cultivation of PCB-respiring Dehalococcoides in pure culture and the identification of PCB-RDase genes deepen our understanding of organohalide respiration of PCBs and shed light on in situ PCB bioremediation.
Summary
1,1,1‐Trichloroethane (TCA) and chloroform are two notorious groundwater pollutants. Here we report the isolation and characterization of Desulfitobacterium sp. strain PR that rapidly ...dechlorinates both compounds. In pyruvate‐amended medium, strain PR reductively dechlorinates ∼ 1.0 mM TCA completely to monochloroethane within 15 days. Under the same conditions, strain PR dechlorinates ∼ 1.2 mM chloroform to predominantly dichloromethane (∼ 1.14 mM) and trace amount of monochloromethane (∼ 0.06 mM) within 10 days. Strain PR shares 96.7% 16S rRNA gene sequence similarity with its closest relative – Desulfitobacterium metallireducens strain 853‐15; however, it distinguishes itself from known Desulfitobacterium strains by its inability of utilizing several of their commonly shared substrates such as lactate, thiosulfate and sulfite. A reductive dehalogenase gene (ctrA) in strain PR was identified to be responsible for dechlorination of both TCA and chloroform, showing a maximum expression level of 5.95 ∼ 6.25 copies of transcripts cell‐1. CtrA shares 94% amino acid sequence identity with CfrA in Dehalobacter sp. strain CF50 and DcrA in Dehalobacter sp. strain DCA. Interestingly, strain PR could tolerate high aqueous concentrations (up to 0.45 mM) of trichloroethene, another groundwater pollutant that often coexists with TCA/chloroform. As the first chloroform‐respiring and the second TCA‐respiring isolate that has been identified, Desulfitobacterium sp. strain PR may prove useful in remediation of halogenated alkanes with trihalomethyl (‐CX3) groups.
As we increasingly integrate technology into our lives, we need a better framework for understanding social interactions across the communication landscape. Utilizing survey data in which more than ...4,600 people across the United States, India, and Japan described a recent social interaction, this article qualitatively and quantitatively explores what makes an interaction meaningful. A qualitative analysis of respondents’ own words finds that meaningful interactions are those with emotional, informational, or tangible impact that people believe enhance their lives, the lives of their interaction partners, or their personal relationships. A quantitative analysis predicting respondents’ ratings of recent interactions finds the attributes most likely to facilitate meaningfulness include strong ties (e.g., friends and family), community ties (e.g., neighbors), shared activities, and synchronicity; meaningful social interactions are also more likely to be planned in advance and memorialized with photos or videos. These attributes are consistent across cultures. Although popular rhetoric often juxtaposes people’s online lives against their offline lives, this research finds in-person interactions can be just as meaningful as technology-mediated interactions. We conclude with a new framework for thinking about social interactions more holistically.
1,1,2-trichloroethane (1,1,2-TCA) has become a common groundwater pollutant due to historically extensive utilization, improper disposal, as well as from incomplete dechlorination of ...1,1,2,2-tetrachloroethane. Currently, limited information is available on microbial detoxification of 1,1,2-TCA. Desulfitobacterium sp. strain PR, which was isolated from an anaerobic bioreactor maintained to dechlorinate chloroethenes/ethanes, exhibited the capacity to dechlorinate 1,1,1-trichloroethane and chloroform. In this study, the dechlorinating ability of strain PR was further explored. Strain PR showed the capability to dechlorinate 1,1,2-TCA (~1.12 mM) predominantly to 1,2-dichloroethane (1,2-DCA) and chloroethane, and to trace amounts of vinyl chloride and ethene within 20 days. Strain PR coupled growth with dechlorination of 1,1,2-TCA to 1,2-DCA, while no cell growth was observed with dechlorination of 1,2-DCA to chloroethane. Later, through transcriptomic and enzymatic analysis, the reductive dehalogenase CtrA, which was previously reported to be responsible for 1,1,1-trichloroethane and chloroform dechlorination, was identified as the 1,1,2-TCA reductive dehalogenase. Since trichloroethene (TCE) is usually co-contaminated with 1,1,2-TCA, a co-culture containing Dehalococcoides mccartyi strain 11a capable of detoxifying TCE and 1,2-DCA and strain PR was established. Interestingly, this co-culture dechlorinated 1,1,2-TCA and TCE to the non-toxic end-product ethene within 48 days without chloroethane production. This novel pathway avoids production of the carcinogenic intermediate dechlorination product vinyl chloride, providing a more environmentally friendly strategy to treat 1,1,2-TCA.
Purpose
Denitrification process in agricultural fields is a large source of nitrous oxide (N
2
O) emitted to the atmosphere. The rhizosphere soils tend to be the hotspots of denitrification in ...agricultural soils. Recent studies have reported the important role of
nos
Z II in eliminating N
2
O. However, little was known about how these more recently discovered N
2
O-reducing microorganisms together with other N
2
O-producers affected the N
2
O emission in agricultural rhizosphere soils.
Materials and methods
Here, we compared the potential N
2
O production rate, the denitrification end-product ratio, and the denitrifier communities between rhizosphere and non-rhizosphere soils of two types of crops in winter and summer. The potential activities were measured by acetylene inhibition technique. QPCR analysis was used to quantify the functional genes. High-throughput sequencing and clone library were conducted to analyze the community structure of denitrifiers.
Results and discussion
The rhizosphere soils had a higher N
2
O production potential but lower denitrification end-product ratio (N
2
O/(N
2
O+N
2
)) than the non-rhizosphere soils. The potential N
2
O production rate was correlated to the
nir
S-bacteria abundance, especially in terms of the genus
Azospirillum
. The N
2
O/(N
2
O+N
2
) ratio showed a negative correlation with both the diversity and abundance of the
nos
Z II-type N
2
O-reducers.
Conclusions
Altogether, we propose that
nir
S-type N
2
O-producers and
nos
Z II-type N
2
O-reducers can affect the N
2
O emission in agricultural rhizosphere soils, and enhancement of diversity and abundance of
nos
Z II-type N
2
O-reducers may help with the N
2
O mitigation from upland crops.
Extensive utilization of polybrominated diphenyl ethers (PBDEs) as flame retardants since the 1960s in a variety of commercial products has resulted in ubiquitous environmental distribution of ...commercial PBDE mixtures. Dangers posed to biological populations became apparent after the discovery of elevated levels of PBDEs in biota, most notably in human breast milk and tissues. Environmental persistence of PBDEs results in significant transboundary displacement, threatening fragile ecosystems globally. Despite efforts to curtail usage of PBDEs, public concern remains about the effects of legacy PBDEs contamination and continued discharge of PBDEs in regions lacking restrictions on usage and manufacture. Among available technologies for remediation of PBDEs such as
soil washing, electrokinetic degradation, and biodegradation, this review focuses on bioremediation by microbes under anaerobic conditions. Bioremediation is generally preferred as it is less disruptive to contaminated ecosystems, is cost-effective, and can be implemented at sites that may be inaccessible to more traditional
methods. The aims of this review are to (1) summarize current knowledge of anaerobic microbes that debrominate PBDEs and their associated synergistic partnerships with non-dehalogenating microbes; (2) explore current understandings of the metabolic reductive debromination of PBDE congeners; (3) discuss recent discoveries on dehalogenase genes involved in debromination of PBDEs.
Greenhouse gases such as CH4 generated by forest fires have a significant impact on atmospheric methane concentrations and terrestrial vegetation methane budgets. Verification in conjunction with ...“top-down” satellite remote sensing observation has become a vital way to verify biomass-burning emission inventories and accurately assess greenhouse gases while looking into the limitations in reliability and quantification of existing “bottom-up” biomass-burning emission inventories. Therefore, we considered boreal forest fire regions as an example while combining five biomass-burning emission inventories and CH4 indicators of atmospheric concentration satellite observation data. By introducing numerical comparison, correlation analysis and trend consistency analysis methods, we explained the lag effect between emissions and atmospheric concentration changes and evaluated a more reliable emission inventory using time series similarity measurement methods. The results indicated that total methane emissions from five biomass-burning emission inventories differed by a factor of 2.9 in our study area, ranging from 2.02 to 5.84 Tg for methane. The time trends of the five inventories showed good consistency, with the Quick Fire Emissions Dataset version 2.5 (QFED2.5) having a higher correlation coefficient (above 0.8) with the other four datasets. By comparing the consistency between the inventories and satellite data, a lagging effect was found to be present between the changes in atmospheric concentration and gas emissions caused by forest fires on a seasonal scale. After eliminating lagging effects and combining time series similarity measures, the QFED2.5 (Euclidean distance = 0.14) was found to have the highest similarity to satellite data. In contrast, Global Fire Emissions Database version 4.1 with small fires (GFED4.1s) and Global Fire Assimilation System version 1.2 (GFAS1.2) had larger Euclidean distances of 0.52 and 0.4, respectively, which meant that they had lower similarity to satellite data. Therefore, QFED2.5 was found to be more reliable while having higher application accuracy compared to the other four datasets in our study area. This study further provided a better understanding of the key role of forest fire emissions in atmospheric CH4 concentrations and offered reference for selecting appropriate biomass burning emission inventory datasets for bottom-up inventory estimation studies.
Microplastics and nanoplastics are emerging pollutants that substantially influence biological element cycling in natural ecosystems. Plastics are also prevalent in sewage, and they accumulate in ...waste‐activated sludge (WAS). However, the impacts of plastics on the methanogenic digestion of WAS and the underpinning microbiome remain underexplored, particularly during long‐term operation. In this study, we found that short‐term exposure to individual microplastics and nanoplastics (polyethylene, polyvinyl chloride, polystyrene, and polylactic acid) at a low concentration (10 particles/g sludge) slightly enhanced methanogenesis by 2.1%−9.0%, whereas higher levels (30−200 particles/g sludge) suppressed methanogenesis by 15.2%−30.1%. Notably, the coexistence of multiple plastics, particularly at low concentrations, showed synergistic suppression of methanogenesis. Unexpectedly, methanogenesis activity completely recovered after long‐term exposure to plastics, despite obvious suppression of methanogenesis by initial plastic exposure. The inhibition of methanogenesis by plastics could be attributed to the stimulated generation of reactive oxygen species. The stress induced by plastics dramatically decreased the relative abundance of methanogens but showed marginal influence on putative hydrolytic and fermentation populations. Nonetheless, the digestion sludge microbiome exhibited resilience and functional redundancy, contributing to the recovery of methanogenesis during the long‐term operation of digesters. Plastics also increased the complexity, modularity, and negative interaction ratios of digestion sludge microbiome networks, but their influence on community assembly varied. Interestingly, a unique plastisphere was observed, the networks and assembly of which were distinct from the sludge microbiome. Collectively, the comprehensive evaluation of the influence of microplastics and nanoplastics on methanogenic digestion, together with the novel ecological insights, contribute to better understanding and manipulating this engineered ecosystem in the face of increasing plastic pollution.
Impact statement
Methanogenic digestion is widely applied to recover energy from waste‐activated sludge (WAS) and decreases its harm to public health. Microplastics and nanoplastics are emerging pollutants that may interfere with ecosystem functions. However, a comprehensive understanding of the impacts of plastics on the methanogenic digestion of WAS and the underpinning microbiome has not been achieved. Our study systematically investigated the short‐ and long‐term influence of microplastics and nanoplastics on methanogenic digestion and reported the long‐term recovery behavior of methanogenesis activity for the first time. Novel ecological insights into the influence of plastics on the digestion microbiome were also provided. Our findings suggest that plastics can be an important factor in diagnosing and manipulating digester performance and microbiome.
PDF
