title: Oxygenic denitrification and anaerobic digestion
title: microbial processes addressing agricultural pollution
titleType: Subtitle
Creators: name: Schmitz, Emily V
Publisher: name: University of Iowa
Year: 2024
Subjects: agricultural pollution
anaerobic digestion
microbiome
oxygenic denitrification
Bioremediation
Climate Change

description: The Midwestern United States is a leading worldwide producer of corn and soybeans, directly linked to hog and cattle production. The resulting intensive agricultural production contributes to NO3 - pollution through nutrient runoff and climate change via N2O and CH4 emissions, negatively impacting human and environmental health. Promising technologies and strategies leveraging microbial processes are increasingly implemented to sustainably address Midwest agricultural pollution. However, these biotechnologies have limitations that hinder their successful implementation and usefulness. Therefore, this work aims to fill knowledge gaps in applicable microbial processes to inform better strategies and technologies addressing nutrient runoff and greenhouse gas emissions from Midwest agriculture.
description: This work facilitates identifying and potentially stimulating oxygenic denitrification, a unique nitrogen cycling process currently overlooked in agricultural settings, to inform its use in NO3 - and N2O mitigation strategies. The diversity, distribution, and abundance of the nitric oxide dismutase (nod) gene, a biomarker distinguishing oxygenic denitrification, was investigated in freshwater sediments and agricultural soils in Iowa. DNA analysis revealed greater diversity and abundance of nod sequences from agricultural soils than freshwater sediments. Our phylogenetic analysis of 88 recovered nod sequences improved understanding of nod gene diversity and distribution in the environment, showcased the importance of using nod as a biomarker for identifying oxygenic denitrification compared to other biomarkers, and demonstrated that this process was occurring in agricultural soils for potential stimulation and use. Finally, we demonstrated a more than ten-fold increase in relative nod abundance and an almost nine-fold increase in relative Methylomirabilota (a known phylum including oxygenic denitrifying bacteria) abundance in fully saturated soils compared to variably saturated soils. This finding improves our limited understanding of environmental factors affecting oxygenic denitrifying bacteria and, subsequently, the potential to stimulate them as a denitrification strategy. Overall, this work positively contributes to the understanding of nod genes, and thus oxygenic denitrification, in agricultural settings, advancing the use of this unique microbial process for sustainable NO3 - and N2O mitigation at agricultural sites.
description: Anaerobic digestion of cattle manure is a currently underutilized microbial-driven technology that turns waste into beneficial products while minimizing emissions of NO3 - , N2O, and CH4. Therefore, this work aims to expand the use and potential benefits of on-farm AD by broadening the range of viable waste feedstocks and improving our understanding of how microbiomes influence digester operation. The chemical and microbial responses to changes in the carbon-to-nitrogen ratio (C:N) and organic loading rate (OLR) during anaerobic co-digestion of cattle manure digestate mixed with industrial organics were characterized. C:Ns of 25 and 35 with OLRs ≤ 4 gVS L-1 d-1 maintained stable methane production between 0.33 and 0.39 gVS L-1 d-1. Using 16S rRNA high-throughput sequencing coupled with PICRUSt2, taxonomy and mapped predicted gene abundances were associated with the major anaerobic digestion stages. C:N (25, 35) and OLR (2, 4 gVS L-1 d-1) had minimal impacts on community structure and function, with a slight but notable increase in acetoclastic methanogens and alpha/beta diversity (Shannon and Bray-Curtis) at C:N 35. Digestion was unsustainable at C:N 35 and OLR 6.5 gVS L-1 d-1, revealed by low methane production and souring. Souring correlated with increased hydrolysis and acidogenesis driven by Prevotellaceae. The microbial data indicated the potential of souring before the chemical data. Overall, our comprehensive investigation informs critically needed strategies for high methane production and efficient anaerobic digester operation, as this waste-to-energy technology is increasingly implemented to address agricultural pollution and climate change.