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Duggan DiDominic KL, Shapleigh JP, Walter MT, Wang YS, Reid MC, Regan JM. Microbial diversity and gene abundance in denitrifying bioreactors: A comparison of the woodchip surface biofilm versus the interior wood matrix. JOURNAL OF ENVIRONMENTAL QUALITY 2024. [PMID: 39014985 DOI: 10.1002/jeq2.20600] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/02/2024] [Accepted: 06/20/2024] [Indexed: 07/18/2024]
Abstract
Excessive amounts of nitrogen (N) and phosphorus (P) can lead to eutrophication in water sources. Woodchip bioreactors have shown success in removing N from agricultural runoff, but less is known regarding P removal. Woodchip bioreactors are subsurface basins filled with woodchips installed downgradient of agricultural land to collect and treat drainage runoff. Microorganisms use the woodchips as a carbon (C) source to transform N in the runoff, with unresolved biological impacts on P. This study aims to explore microbial communities present in the bioreactor and determine whether milling woodchips to probe the microbial communities within them reveals hidden microbial diversities or potential activities. Metagenomic sequencing and bioinformatic analyses were performed on six woodchip samples (i.e., three unmilled and three milled) collected from a 10-year-old woodchip bioreactor treating agricultural tile drainage. All samples had similar DNA purity, yield, quality, and microbial diversity regardless of milling. However, when sequences were aligned against various protein libraries, our results indicated greater relative abundance of denitrification and P transformation proteins on the outside of the woodchips (unmilled), while the interior of woodchips (milled) exhibited more functional gene abundance for carbohydrate breakdown. Thus, it may be important to characterize microbial communities both within woodchips, and on woodchip surfaces, to gain a more holistic understanding of coupled biogeochemical cycles on N, P, and C in woodchip bioreactors. Based on these findings, we advise that future microbial research on woodchips (and potentially other permeable organic materials) examine both the surface biofilm and the interior organic material during initial studies. Once researchers determine where specific proteins or enzymes of interest are most prevalent, subsequent studies may then focus on either one or both aspects, as needed.
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Affiliation(s)
- Katie L Duggan DiDominic
- Department of Biological & Environmental Engineering, College of Agriculture and Life Sciences, Cornell University, Ithaca, New York, USA
| | - James P Shapleigh
- Deparment of Microbiology, College of Agriculture and Life Sciences, Cornell University, Ithaca, New York, USA
| | - M Todd Walter
- Department of Biological & Environmental Engineering, College of Agriculture and Life Sciences, Cornell University, Ithaca, New York, USA
| | - Y Samuel Wang
- Department of Statistics & Data Science, College of Agriculture and Life Sciences & College of Computing and Information Science, Cornell University, Ithaca, New York, USA
| | - Matthew C Reid
- Department of Civil & Environmental Engineering, College of Engineering, Cornell University, Ithaca, New York, USA
| | - John M Regan
- Department of Civil & Environmental Engineering, College of Engineering, The Pennsylvania State University, University Park, Pennsylvania, USA
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2
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Shu W, Zhang Q, Audet J, Li Z, Leng P, Qiao Y, Tian C, Chen G, Zhao J, Cheng H, Li F. Non-negligible N 2O emission hotspots: Rivers impacted by ion-adsorption rare earth mining. WATER RESEARCH 2024; 251:121124. [PMID: 38237464 DOI: 10.1016/j.watres.2024.121124] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/19/2023] [Revised: 12/06/2023] [Accepted: 01/08/2024] [Indexed: 02/12/2024]
Abstract
Rare earth mining causes severe riverine nitrogen pollution, but its effect on nitrous oxide (N2O) emissions and the associated nitrogen transformation processes remain unclear. Here, we characterized N2O fluxes from China's largest ion-adsorption rare earth mining watershed and elucidated the mechanisms that drove N2O production and consumption using advanced isotope mapping and molecular biology techniques. Compared to the undisturbed river, the mining-affected river exhibited higher N2O fluxes (7.96 ± 10.18 mmol m-2d-1 vs. 2.88 ± 8.27 mmol m-2d-1, P = 0.002), confirming that mining-affected rivers are N2O emission hotspots. Flux variations scaled with high nitrogen supply (resulting from mining activities), and were mainly attributed to changes in water chemistry (i.e., pH, and metal concentrations), sediment property (i.e., particle size), and hydrogeomorphic factors (e.g., river order and slope). Coupled nitrification-denitrification and N2O reduction were the dominant processes controlling the N2O dynamics. Of these, the contribution of incomplete denitrification to N2O production was greater than that of nitrification, especially in the heavily mining-affected reaches. Co-occurrence network analysis identified Thiomonas and Rhodanobacter as the key genus closely associated with N2O production, suggesting their potential roles for denitrification. This is the first study to elucidate N2O emission and influential mechanisms in mining-affected rivers using combined isotopic and molecular techniques. The discovery of this study enhances our understanding of the distinctive processes driving N2O production and consumption in highly anthropogenically disturbed aquatic systems, and also provides the foundation for accurate assessment of N2O emissions from mining-affected rivers on regional and global scales.
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Affiliation(s)
- Wang Shu
- Shandong Yucheng Agro-Ecosystem National Observation and Research Station, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China; Sino-Danish College of University of Chinese Academy of Sciences, Beijing 101408, China; Sino-Danish Centre for Education and Research, Beijing 101408, China
| | - Qiuying Zhang
- State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China.
| | - Joachim Audet
- Department of Ecoscience, Aarhus University, C.F. Møllers Allé, Aarhus 8000, Denmark
| | - Zhao Li
- Shandong Yucheng Agro-Ecosystem National Observation and Research Station, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China
| | - Peifang Leng
- Shandong Yucheng Agro-Ecosystem National Observation and Research Station, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China
| | - Yunfeng Qiao
- Shandong Yucheng Agro-Ecosystem National Observation and Research Station, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China
| | - Chao Tian
- Shandong Yucheng Agro-Ecosystem National Observation and Research Station, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China
| | - Gang Chen
- Department of Civil and Environmental Engineering, Florida A&M University (FAMU)-Florida State University (FSU) Joint College of Engineering, 32310, United States
| | - Jun Zhao
- School of Geography and Ocean Science, Nanjing University, Nanjing 210023, China
| | - Hefa Cheng
- MOE Laboratory for Earth Surface Processes, College of Urban and Environmental Sciences, Peking University, Beijing 100871, China
| | - Fadong Li
- Shandong Yucheng Agro-Ecosystem National Observation and Research Station, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China; Sino-Danish College of University of Chinese Academy of Sciences, Beijing 101408, China.
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3
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Jéglot A, Miranda-Velez JF, Plauborg F, Elsgaard L. Nitrate removal and environmental side-effects controlled by hydraulic residence time in woodchip bioreactors treating cold agricultural drainage water. ENVIRONMENTAL TECHNOLOGY 2023; 44:4324-4333. [PMID: 35722770 DOI: 10.1080/09593330.2022.2091482] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/15/2022] [Accepted: 06/09/2022] [Indexed: 06/15/2023]
Abstract
Denitrifying woodchip bioreactors (WBRs) remove nitrate (NO 3 - ) from agricultural drainage water at field-scale, but their efficacy at cold temperatures remains uncertain. This study shows how hydraulic residence time (HRT) controls NO 3 - removal and environmental side-effects of WBRs at low water temperature under pilot-scale conditions with controlled operation of nine WBRs (94 dm3). Hydraulic properties were assessed by a bromide tracer test, and NO 3 - removal, emissions of nitrous oxide (N2O) and methane (CH4), and losses of dissolved organic carbon (DOC) were measured at HRTs of 5-30 h. Inlet NO 3 - concentrations were increasingly reduced at higher HRTs. The relationship between HRT and the efficiency (%) of NO 3 - removal was linear (R a d j 2 = 0.94), while the relationship between HRT and NO 3 - reduction rates (NRR) was logistic (R a d j 2 = 0.88). Gaseous emissions of N2O were equally low at HRTs of 10-30 h, but higher at 5 h (P < 0.05). Methane fluxes were small, but with consistent emissions at HRTs of 20-30 h and uptake at 5-15 h. HRT had limited effect on effluent DOC concentrations, but strong effect on mass losses that were five-fold higher (320 mg L-1) at the HRT of 5 h than at 30 h. In summary, at cold temperatures HRTs of ≤ 20 h resulted in suboptimal NRR, accelerating DOC losses, and increased risk of N2O losses at least below a threshold HRT of 5-10 h. HRTs of 20-30 h gave maximal NRR, smallest losses of DOC and N2O, but an increased risk of CH4 emissions.
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Affiliation(s)
- Arnaud Jéglot
- Department of Agroecology, Aarhus University, Tjele, Denmark
- WATEC, Department of Agroecology, Aarhus University, Tjele, Denmark
| | | | - Finn Plauborg
- Department of Agroecology, Aarhus University, Tjele, Denmark
- WATEC, Department of Agroecology, Aarhus University, Tjele, Denmark
| | - Lars Elsgaard
- Department of Agroecology, Aarhus University, Tjele, Denmark
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Buyanjargal A, Kang J, Lee JH, Jeen SW. Nitrate removal rates, isotopic fractionation, and denitrifying bacteria in a woodchip-based permeable reactive barrier system: a long-term column experiment. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2023; 30:36364-36376. [PMID: 36547843 DOI: 10.1007/s11356-022-24826-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/10/2022] [Accepted: 12/14/2022] [Indexed: 06/17/2023]
Abstract
This study evaluated the effectiveness of using organic carbon materials (i.e., woodchips) to remove nitrate from groundwater. The results of our flow-through column experiment, which was conducted over 1.6 years, suggested that denitrifying bacteria reduce nitrate by using it as an electron acceptor and woodchips as an electron donor. The nitrate removal rates were sufficiently high (0.39-1.04 mmol L-1 day-1) during the operation of the column. Denitrification process was supported by fractionation of nitrogen and oxygen isotopes (δ15N and δ18O), with the δ15N and δ18O values enriched from 7.4‰ and 22.3‰ to 21.2‰ and 30.4‰, respectively. Enrichment factors ([Formula: see text]) for 15 N and 18O were calculated using the Rayleigh fractionation model, with values of - 13.2‰ for ε15N and - 7.1‰ for ε18O. The fractionation ratio of 15 N to 18O was 1.9:1, confirming denitrification. The most abundant bacterial genera in the soil used for inoculation were Enterobacter (86.7%), Nitrospira (1.8%), and Arthrobacter (1.5%), while those in the column effluent were Macrococcus (37.1%), Escherichia (14.7%), and Shigella (14.6%), indicating that bacterial communities changed in response to geochemical conditions in the column. This study suggests that nitrate in groundwater can be effectively removed using woodchip-based passive treatment systems and that information on isotopic fractionation and denitrifying bacteria can be key tools to understand denitrification.
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Affiliation(s)
- Altantsetseg Buyanjargal
- Department of Earth and Environmental Sciences & The Earth and Environmental Science System Research Center, Jeonbuk National University, Jeonju-Si, Jeollabuk-Do, 54896, Republic of Korea
- Milko Company, Teso Corporation, Ulaanbaatar, Mongolia
| | - Jiyoung Kang
- Department of Environment and Energy, Jeonbuk National University, Jeonju-Si, Jeollabuk-Do, 54896, Republic of Korea
| | - Ji-Hoon Lee
- Department of Bioenvironmental Chemistry, Jeonbuk National University, Jeonju-Si, Jeollabuk-Do, 54896, Republic of Korea
| | - Sung-Wook Jeen
- Department of Earth and Environmental Sciences & The Earth and Environmental Science System Research Center, Jeonbuk National University, Jeonju-Si, Jeollabuk-Do, 54896, Republic of Korea.
- Department of Environment and Energy, Jeonbuk National University, Jeonju-Si, Jeollabuk-Do, 54896, Republic of Korea.
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5
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Zhu Z, Li X, Bu Q, Yan Q, Wen L, Chen X, Li X, Yan M, Jiang L, Chen G, Li S, Gao X, Zeng G, Liang J. Land-Water Transport and Sources of Nitrogen Pollution Affecting the Structure and Function of Riverine Microbial Communities. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2023; 57:2726-2738. [PMID: 36746765 DOI: 10.1021/acs.est.2c04705] [Citation(s) in RCA: 11] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
The characterization of variations in riverine microbiota that stem from contaminant sources and transport modes is important for understanding biogeochemical processes. However, the association between complex anthropogenic nitrogen pollution and bacteria has not been extensively investigated owing to the difficulties faced while determining the distribution of nitrogen contaminants in watersheds. Here, we employed the Soil and Water Assessment Tool alongside microbiological analysis to explore microbial characteristics and their responses to complex nitrogen pollution patterns. Significant variations in microbial communities were observed in sub-basins with distinct land-water pollution transport modes. Point source-dominated areas (PSDAs) exhibited reduced microbial diversity, high number of denitrification groups, and increased nitrogen cycling compared with others. The negative relative deviations (-3.38) between the measured and simulated nitrate concentrations in PSDAs indicated that nitrate removal was more effective in PSDAs. Pollution sources were also closely associated with microbiota. Effluents from concentrated animal feeding operations were the primary factors relating to the microbiota compositions in PSDAs and balanced areas. In nonpoint source-dominated areas, contaminants from septic tanks become the most relevant sources to microbial community structures. Overall, this study expands our knowledge regarding microbial biogeochemistry in catchments and beyond by linking specific nitrogen pollution scenarios to microorganisms.
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Affiliation(s)
- Ziqian Zhu
- College of Environmental Science and Engineering, Hunan University, Changsha 410082, P. R. China
- Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha 410082, P. R. China
| | - Xin Li
- College of Environmental Science and Engineering, Hunan University, Changsha 410082, P. R. China
- Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha 410082, P. R. China
| | - Qiurong Bu
- National Engineering Research Centre of Advanced Technologies and Equipment for Water Environmental Pollution Monitoring, Changsha 410205, P. R. China
| | - Qingcheng Yan
- National Engineering Research Centre of Advanced Technologies and Equipment for Water Environmental Pollution Monitoring, Changsha 410205, P. R. China
| | - Liqun Wen
- National Engineering Research Centre of Advanced Technologies and Equipment for Water Environmental Pollution Monitoring, Changsha 410205, P. R. China
| | - Xiaolei Chen
- National Engineering Research Centre of Advanced Technologies and Equipment for Water Environmental Pollution Monitoring, Changsha 410205, P. R. China
| | - Xiaodong Li
- College of Environmental Science and Engineering, Hunan University, Changsha 410082, P. R. China
- Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha 410082, P. R. China
| | - Ming Yan
- College of Environmental Science and Engineering, Hunan University, Changsha 410082, P. R. China
- Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha 410082, P. R. China
| | - Longbo Jiang
- College of Environmental Science and Engineering, Hunan University, Changsha 410082, P. R. China
- Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha 410082, P. R. China
| | - Gaojie Chen
- School of Mathematics, Hunan University, Changsha 410082, P. R. China
| | - Shuai Li
- College of Environmental Science and Engineering, Hunan University, Changsha 410082, P. R. China
- Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha 410082, P. R. China
| | - Xiang Gao
- College of Environmental Science and Engineering, Hunan University, Changsha 410082, P. R. China
- Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha 410082, P. R. China
| | - Guangming Zeng
- College of Environmental Science and Engineering, Hunan University, Changsha 410082, P. R. China
- Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha 410082, P. R. China
| | - Jie Liang
- College of Environmental Science and Engineering, Hunan University, Changsha 410082, P. R. China
- Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha 410082, P. R. China
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6
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Liu YY. Controlling the human microbiome. Cell Syst 2023; 14:135-159. [PMID: 36796332 PMCID: PMC9942095 DOI: 10.1016/j.cels.2022.12.010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2022] [Revised: 10/18/2022] [Accepted: 12/21/2022] [Indexed: 02/17/2023]
Abstract
We coexist with a vast number of microbes that live in and on our bodies. Those microbes and their genes are collectively known as the human microbiome, which plays important roles in human physiology and diseases. We have acquired extensive knowledge of the organismal compositions and metabolic functions of the human microbiome. However, the ultimate proof of our understanding of the human microbiome is reflected in our ability to manipulate it for health benefits. To facilitate the rational design of microbiome-based therapies, there are many fundamental questions to be addressed at the systems level. Indeed, we need a deep understanding of the ecological dynamics associated with such a complex ecosystem before we rationally design control strategies. In light of this, this review discusses progress from various fields, e.g., community ecology, network science, and control theory, that are helping us make progress toward the ultimate goal of controlling the human microbiome.
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Affiliation(s)
- Yang-Yu Liu
- Channing Division of Network Medicine, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115, USA; Center for Artificial Intelligence and Modeling, The Carl R. Woese Institute for Genomic Biology, University of Illinois at Urbana-Champaign, Champaign, IL 61801, USA.
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7
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Van Aken P, Lambert N, Appels L. Low temperature Moving Bed Bioreactor denitrification as mitigation measure to reduce agricultural nitrate losses. THE SCIENCE OF THE TOTAL ENVIRONMENT 2022; 810:152110. [PMID: 34871692 DOI: 10.1016/j.scitotenv.2021.152110] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/20/2021] [Revised: 11/07/2021] [Accepted: 11/27/2021] [Indexed: 06/13/2023]
Abstract
The negative impact of agriculture on the quality of local water streams is widely recognized. Fertilizer residues not taken up by the crops leach into the drainage water and enter the surface water, resulting in eutrophication. Despite various initiatives to prevent this leaching by optimizing fertilizer schemes, the desired effect was not achieved, and the focus has shifted to denitrifying end-of-pipe techniques. Because the available area for installing such treatment systems is often limited, the development of intensified systems is a trend that has emerged recently. In this scope, the main goal of this study was therefore to investigate the suitability of a denitrifying Moving Bed Bioreactor (MBBR) as a low footprint technology, which can compete with conventional technologies. Two parallel lab-scale pilot MBBRs, one at low temperature and one at ambient temperature, were operated for 850 days to investigate the effectiveness and robustness under changing process parameters (hydraulic retention time (HRT), temperature, shutdown). Eventually, the system was scaled up to a full-scale installation and monitored during a full drainage season in the field. The pilot-scale MBBRs achieved removal efficiencies above 90% under optimal conditions (high C/N ratio and minimal HRT of 8 h), even while operating at low temperatures. The robustness of the system was also demonstrated by the immediate start-up after a shutdown period of 220 days. Overall, the full-scale MBBR treated 2910.1 m3 drainage water and removed approximately 59 kg NO3-N. Unfortunately, the average removal efficiency, i.e., 70%, was lower than the lab-scale system, but by intensifying the mixing in the MBBR, improved results were obtained. Nitrite accumulation was furthermore also prevented.
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Affiliation(s)
- Pieter Van Aken
- KU Leuven, Department of Chemical Engineering, Process and Environmental Technology Lab, J. De Nayerlaan 5, 2860 Sint-Katelijne-Waver, Belgium
| | - Nico Lambert
- KU Leuven, Department of Chemical Engineering, Process and Environmental Technology Lab, J. De Nayerlaan 5, 2860 Sint-Katelijne-Waver, Belgium
| | - Lise Appels
- KU Leuven, Department of Chemical Engineering, Process and Environmental Technology Lab, J. De Nayerlaan 5, 2860 Sint-Katelijne-Waver, Belgium.
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8
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Schaefer A, Lee J, Soupir ML, Moorman TB, Howe A. Comparison of microbial communities in replicated woodchip bioreactors. JOURNAL OF ENVIRONMENTAL QUALITY 2022; 51:205-215. [PMID: 34965312 DOI: 10.1002/jeq2.20320] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/14/2021] [Accepted: 12/16/2021] [Indexed: 06/14/2023]
Abstract
Denitrification in woodchip bioreactors is a microbial process, but the effects of variations in bioreactors operation on microbial community structure are not well understood. Here, our goals were to understand hydraulic retention time (HRT) as a factor that influences woodchip bioreactor microbial community variation and structure in replicated field bioreactors and to evaluate relationships between microbial community membership and marker genes for denitrification. We used a combination of quantitative polymerase chain reaction of nirS, nirK, nosZI, and nosZII and 16S rRNA amplicon sequencing to characterize the microbial communities of nine pilot-scale woodchip bioreactors located at Iowa State University. Our results showed dynamic microbial communities but with persistent taxa between two sampling years and three HRTs. Similarities between functional gene copy numbers across sampling year and HRT indicate that the potential for denitrification is conserved despite differences in the microbial communities. These results are evidence that there are specific and persistent taxa within replicated bioreactors. Woodchip bioreactor microbial community membership is recommended to be the focus of future studies to better understand the relationship between microbial community functions and bioreactor management.
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Affiliation(s)
- Abby Schaefer
- Dep. of Agricultural and Biosystems Engineering, Iowa State Univ., Ames, IA, 50011, USA
| | - Jaejin Lee
- Genomics and Environmental Research in Microbial Systems Laboratory, Dep. of Agricultural and Biosystems Engineering, Iowa State Univ., 3346 Elings Hall, Ames, IA, 50011, USA
| | - Michelle L Soupir
- Water Quality Research Laboratory, Dep. of Agricultural and Biosystems Engineering, Iowa State Univ., 3358 Elings Hall, Ames, IA, 50011, USA
| | - Thomas B Moorman
- USDA-ARS, National Laboratory for Agriculture and the Environment, 2110 University Blvd., Ames, IA, 50011, USA
| | - Adina Howe
- Genomics and Environmental Research in Microbial Systems Laboratory, Dep. of Agricultural and Biosystems Engineering, Iowa State Univ., 3346 Elings Hall, Ames, IA, 50011, USA
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