Application : NO2 Degradation
Synthetic nitrogen fertilizer is typically over-applied in farming practices to account for plant uptake and loss of nitrogen to the environment.
WHY THIS IS ON OUR RADAR
Nitrous oxide (N2O) is a potent greenhouse gas with a global warming potential about 273 times greater than CO2 over a 100-year period. N2O emissions have a significant impact on climate change and a role in ozone layer depletion
The primary sources of N2O emissions are agricultural practices, especially the use of synthetic nitrogen fertilizers. Synthetic nitrogen fertilizer is typically overapplied in farming practices to account for plant uptake and loss of nitrogen to the environment.
State-of-the-art:
Industrial fertilizer: Synthetic fertilizers enhance soil nitrogen levels, which, through microbial processes, can produce N2O. Improving fertilizer use efficiency and adopting better agricultural practices are key strategies for reducing these emissions.
Agricultural practices to reduce N2O: For row crops (corn, soy, etc.), use of soil sensors or crop models to guide more efficient fertilizer application; use of slow-release fertilizers that include a coat with urea and nitrification inhibitors that slow the conversion of ammonium to nitrate, a process that produces N2O; cover crops and rotating crops can enhance soil health and reduce N2O emissions. For cattle excreta on grazing lands (16% of N2O emissions), fewer solutions are available [2019].
Microbial N2O degradation: N2O is converted to N2 via nitrous oxide reductase (NosZ). NosZ is oxygen-sensitive, and few organisms express it in aerobic conditions and continue robust N2O reduction [2023]. Few microorganisms exist that, when applied to soil, persistently lower N2O emissions, and they must be specifically isolated [2024].
R&D focus: engineered microorganisms that can more efficiently perform denitrification (e.g. fine-tune regulation of nosZ gene or more efficient metabolic pathways) or other relevant processes (NO3- presence inhibits expression of nosZ) that may lead to new methods for reducing N2O emissions. Understanding which auxiliary genes can contribute to more N2O reduction may help find/design better strains.
Opportunities:
Funding calls: recent ARPA-E call on reduction of N2O emissions from corn and sorghum crops (Teosynte; call summary; call doc).
Leverage genetics: some of the main organisms do not have genetics, while others have limited tools.
Potential for Tn-seq: Tn-seq can help identify auxiliary genes; no genome-wide Tn-seq/RNA-seq analysis (nos/nir/nif gene expression experiments available) on N2O degradation have been identified in the literature.
Assay required: 2 approaches, 1) focus on Tn in the presence of N2O or KNO3; or 2) Tn and measure gas content (O2, NO2/3, N2O, N2) for which GC would be required.
Risks:
Growth set up: It will require setting up a station to exchange with to remove O2 from the culture.
Establishment in soil: not natural inoculants tend to die out rapidly; availability of key nutrients, such as carbon sources for denitrifiers can limit the growth and function; competition with other microorganisms for nutrients and resources can impact the performance of N2O-degrading organisms.
Strain availability: most of the strains are isolates, and in many cases representative examples are not available through strain banks. This might be a good example of a cohort where isolation or getting strains from collaborators might be beneficial.
Strategy for strain selection:
Focus: improvement of N2O denitrification.
Keywords: 2 approaches, 1) Lit search using “N2O-respiring bacteria”, “N2O denitrification”, “nosZ clade”; and 2) search by reaction, nitrous oxide reductase (Rhea) .
Selection: up to 5 organisms; 3 with different levels of genetics (e.g. some replicating vectors but no Tn or recombination), 2 with no genetics in different taxonomic levels.
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