Project description:Oxygen deficient zones (ODZs) are major sites of net natural oceanic nitrous oxide (N2O) production and emissions. In order to understand changes in the magnitude of N2O production in response to global change, knowledge on the individual contributions of the major microbial pathways (nitrification and denitrification) to N2O production and their regulation is needed. In the ODZ of the coastal area off Peru, the sensitivity of N2O production to oxygen and organic matter was investigated using 15N-tracer experiments in combination with qPCR and microarray analysis of total and active functional genes targeting archaeal amoA and nirS as marker genes for nitrification and denitrification, respectively. Denitrification was responsible for the highest N2O production with mean 8.7 nmol L-1 d-1 but up to 118 ± 27.8 nmol L-1 d-1 just below the oxic-anoxic interface. Highest N2O production from AO of 0.16 ± 0.003 nmol L-1 d-1 occurred in the upper oxycline at O2 concentrations of 10 - 30 µmol L-1 which coincided with highest archaeal amoA transcripts/genes. Oxygen responses of N2O production varied with substrate, but production and yields were generally highest below 10 µmol L-1 O2. Particulate organic matter additions increased N2O production by denitrification up to 5-fold suggesting increased N2O production during times of high particulate organic matter export. High N2O yields from ammonium oxidation of 2.1% were measured, but the overall contribution to N2O production stays an order of magnitude behind denitrification as an N2O source. Hence, these findings show that denitrification is the most important N2O production process in low oxygen conditions fueled by organic carbon supply which implies a positive feedback of the total oceanic N2O sources in response to increasing oceanic deoxygenation. [SUBMITTER_CITATION]: Frey, C., Bange, H. W., Achterberg, E. P., Jayakumar, A., Löscher, C. R., Arévalo-Martínez, D. L., León-Palmero, E., Sun, M., Sun, X., Xie, R. C., Oleynik, S., and Ward, B. B.: Regulation of nitrous oxide production in low-oxygen waters off the coast of Peru, Biogeosciences, 17, 2263-2287
Project description:Oxygen deficient zones (ODZs) are major sites of net natural oceanic nitrous oxide (N2O) production and emissions. In order to understand changes in the magnitude of N2O production in response to global change, knowledge on the individual contributions of the major microbial pathways (nitrification and denitrification) to N2O production and their regulation is needed. In the ODZ of the coastal area off Peru, the sensitivity of N2O production to oxygen and organic matter was investigated using 15N-tracer experiments in combination with qPCR and microarray analysis of total and active functional genes targeting archaeal amoA and nirS as marker genes for nitrification and denitrification, respectively. Denitrification was responsible for the highest N2O production with mean 8.7 nmol L-1 d-1 but up to 118 ± 27.8 nmol L-1 d-1 just below the oxic-anoxic interface. Highest N2O production from AO of 0.16 ± 0.003 nmol L-1 d-1 occurred in the upper oxycline at O2 concentrations of 10 - 30 µmol L-1 which coincided with highest archaeal amoA transcripts/genes. Oxygen responses of N2O production varied with substrate, but production and yields were generally highest below 10 µmol L-1 O2. Particulate organic matter additions increased N2O production by denitrification up to 5-fold suggesting increased N2O production during times of high particulate organic matter export. High N2O yields from ammonium oxidation of 2.1% were measured, but the overall contribution to N2O production stays an order of magnitude behind denitrification as an N2O source. Hence, these findings show that denitrification is the most important N2O production process in low oxygen conditions fueled by organic carbon supply which implies a positive feedback of the total oceanic N2O sources in response to increasing oceanic deoxygenation. [SUBMITTER_CITATION]: Frey, C., Bange, H. W., Achterberg, E. P., Jayakumar, A., Löscher, C. R., Arévalo-Martínez, D. L., León-Palmero, E., Sun, M., Sun, X., Xie, R. C., Oleynik, S., and Ward, B. B.: Regulation of nitrous oxide production in low-oxygen waters off the coast of Peru, Biogeosciences, 17, 2263-2287
Project description:Nitrosomonas europaea is a chemolithoautotrophic bacterium that oxidizes ammonia (NH3) to obtain energy for growth on carbon dioxide (CO2), and can also produce nitrous oxide (N2O), a greenhouse gas. We interrogated the growth, physiological, and transcriptome responses of N. europaea to replete (> 5.2 mM) and limited inorganic carbon (IC) provided by either 1.0 mM or 0.2 mM sodium carbonate (Na2CO3) supplemented with atmospheric CO2. IC-limited cultures oxidized 25 to 58% of available NH3 to nitrite, depending on dilution rate and Na2CO3 concentration. IC limitation resulted in a 1.5-fold increase in cellular maintenance energy requirements compared to NH3-limited cultures. Rates of N2O production increased 2- and 6.3 fold under the two IC-limited conditions increasing the percentage of oxidized NH3-N being transformed to N2O-N from 0.5% (replete) to 4.4% (0.25 mM Na2CO3). Transcriptome analysis showed differential expression (p ≤ 0.05) of 488 genes (20% of inventory) between replete and IC-limited conditions, but few differences were detected between the two IC-limiting treatments. IC-limited conditions resulted in decreased expression of ammonium/ammonia transporter and ammonia monooxygenase subunits, and increased expression of genes involved in C1 metabolism including RuBisCO (cbb gene cluster), carbonic anhydrase, folate-linked metabolism of C1 moieties, and putative C salvage due to oxygenase activity of RuBisCO. Increased expression of nitrite reductase (gene cluster NE0924-0927) correlated with increased production of N2O. Together, these data suggest that N. europaea adapts physiologically during IC-limited steady state growth, which leads to uncoupling of NH3 oxidation from growth and increased N2O production.
Project description:Nitrosomonas europaeais a chemolithoautotrophic bacterium that oxidizes ammonia (NH3) to obtain energy for growth on carbon dioxide (CO2), and can also produce nitrous oxide (N2O), a greenhouse gas. We interrogated the growth, physiological, and transcriptome responses ofN. europaeato replete (> 5.2 mM) and limited inorganic carbon (IC) provided by either 1.0 mM or 0.2 mM sodium carbonate (Na2CO3) supplemented with atmospheric CO2 IC-limited cultures oxidized 25 to 58% of available NH3to nitrite, depending on dilution rate and Na2CO3concentration. IC limitation resulted in a 2.3-fold increase in cellular maintenance energy requirements compared to NH3-limited cultures. Rates of N2O production increased 2.5- and 6.3-fold under the two IC-limited conditions increasing the percentage of oxidized NH3-N being transformed to N2O-N from 0.5% (replete) up to 4.4% (0.2 mM Na2CO3). Transcriptome analysis showed differential expression (p⤠0.05) of 488 genes (20% of inventory) between replete and IC-limited conditions, but few differences were detected between the two IC-limiting treatments. IC-limited conditions resulted in decreased expression of ammonium/ammonia transporter and ammonia monooxygenase subunits, and increased expression of genes involved in C1 metabolism including RuBisCO (cbbgene cluster), carbonic anhydrase, folate-linked metabolism of C1 moieties, and putative C salvage due to oxygenase activity of RuBisCO. Increased expression of nitrite reductase (gene cluster NE0924-0927) correlated with increased production of N2O. Together, these data suggest thatN. europaeaadapts physiologically during IC-limited steady state growth, which leads to uncoupling of NH3oxidation from growth and increased N2O production. Transcriptome responses of N. europaea in 60 mM NH4+ to suboptimum levels of carbonate (1.0 mM and 0.2 mM) in continuous steady-state culture in a bioreactor.
Project description:Anaerobic digestion (AD) is a core technology in management of urban organic wastes, converting a fraction of the organic carbon to methane and the residual digestate, the biorest, have a great potential to become a major organic fertilizer for agricultural soils in the future. At the same time, mitigation of N2O-emissions from the agricultural soils is needed to reduce the climate forcing by food production. Our goal was therefore to enrich for N2O reducing bacteria in AD digestates prior to fertilization, and in this way provide an avenue for large-scale and low-cost cultivation of strongly N2O reducing bacteria which can be directly introduced to agricultural soils in large enough volumes to alter the fate of nitrogen in the soils. Gas kinetics and meta-omics (metagenomics and metaproteomics) analyses of the N2O enriched digestates identified populations of N2O respiring organisms that grew by harvesting fermentation intermediates of the methanogenic consortium.
Project description:Nitrous oxide (N(2)O) is a major radiative forcing and stratospheric ozone-depleting gas emitted from terrestrial and aquatic ecosystems. It can be transformed to nitrogen gas (N(2)) by bacteria and archaea harboring the N(2)O reductase (N(2)OR), which is the only known N(2)O sink in the biosphere. Despite its crucial role in mitigating N(2)O emissions, knowledge of the N(2)OR in the environment remains limited. Here, we report a comprehensive phylogenetic analysis of the nosZ gene coding the N(2)OR in genomes retrieved from public databases. The resulting phylogeny revealed two distinct clades of nosZ, with one unaccounted for in studies investigating N(2)O-reducing communities. Examination of N(2)OR structural elements not considered in the phylogeny revealed that the two clades differ in their signal peptides, indicating differences in the translocation pathway of the N(2)OR across the membrane. Sequencing of environmental clones of the previously undetected nosZ lineage in various environments showed that it is widespread and diverse. Using quantitative PCR, we demonstrate that this clade was most often at least as abundant as the other, thereby more than doubling the known extent of the overall N(2)O-reducing community in the environment. Furthermore, we observed that the relative abundance of nosZ from either clade varied among habitat types and environmental conditions. Our results indicate a physiological dichotomy in the diversity of N(2)O-reducing microorganisms, which might be of importance for understanding the relationship between the diversity of N(2)O-reducing microorganisms and N(2)O reduction in different ecosystems.
Project description:N2O-reducing bacteria have been examined and harnessed to develop technologies that reduce the emission of N2O, a greenhouse gas produced by biological nitrogen removal. Recent investigations using omics and physiological activity approaches have revealed the ecophysiologies of these bacteria during nitrogen removal. Nevertheless, their involvement in anammox processes remain unclear. Therefore, the present study investigated the identity, genetic potential, and activity of N2O reducers in an anammox reactor. We hypothesized that N2O is limiting for N2O-reducing bacteria and an exogeneous N2O supply enriches as-yet-uncultured N2O-reducing bacteria. We conducted a 1200-day incubation of N2O-reducing bacteria in an anammox consortium using gas-permeable membrane biofilm reactors (MBfRs), which efficiently supply N2O in a bubbleless form directly to a biofilm grown on a gas-permeable membrane. A 15N tracer test indicated that the supply of N2O resulted in an enriched biomass with a higher N2O sink potential. Quantitative PCR and 16S rRNA amplicon sequencing revealed Clade II nosZ type-carrying N2O-reducing bacteria as protagonists of N2O sinks. Shotgun metagenomics showed the genetic potentials of the predominant Clade II nosZ-carrying bacteria, Anaerolineae and Ignavibacteria in MBfRs. Gemmatimonadota and non-anammox Planctomycetota increased their abundance in MBfRs despite their overall lower abundance. The implication of N2O as an inhibitory compound scavenging vitamin B12, which is essential for the synthesis of methionine, suggested its limited suppressive effect on the growth of B12-dependent bacteria, including N2O reducers. We identified Dehalococcoidia and Clostridia as predominant N2O sinks in an anammox consortium fed exogenous N2O because of the higher metabolic potential of vitamin B12-dependent biosynthesis.
Project description:Here, we successfully used NO as the direct electron acceptor for the enrichment of a microbial community in a continuous bioreactor. The enrichment culture, mainly comprised of two new organisms from the Sterolibacteriaceae family, grew on NO reduction to N2 and formate oxidation, with virtually no accumulation of N2O. The microbial growth kinetics of the enrichment culture as well as its affinity for different N-oxides were determined. In parallel, using metagenomics, metatranscriptomics, and metaproteomics, the biochemical reactions underlying the growth of these microorganisms on NO were investigated. This study demonstrates that microorganisms thrive and can be enriched on NO, and presents new opportunities to study microbial growth on this highly energetic and climate-active molecule that may have been pivotal in the evolution of aerobic respiration.