Leaching of antibiotic resistance genes and microbial assemblages following poultry litter applications in karst and non-karst landscapes

Authors: SEYOUM, MITIKU - University Of Arkansas; Ashworth, Amanda; Owens, Phillip; KATUWAL, SHEELA - Orise Fellow; Lyte, Joshua - Josh; SAVIN, MARY - University Of Arkansas

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/28/2024
Publication Date: 5/17/2024
Citation: Seyoum, M.M., Ashworth, A.J., Owens, P.R., Katuwal, S., Lyte, J.M., Savin, M. 2024. Leaching of antibiotic resistance genes and microbial assemblages following poultry litter applications in karst and non-karst landscapes. Science of the Total Environment. 934. Article 172905. https://doi.org/10.1016/j.scitotenv.2024.172905.
DOI: https://doi.org/10.1016/j.scitotenv.2024.172905

Interpretive Summary: Karst landscapes are formed by natural dissolution of soluble rocks, resulting in direct surface to subsurface contact and cover approximately 25% of the continental U.S. landmass. Livestock manures are valuable fertilizer sources but may also contain antimicrobial resistant bacteria. As depending on antibiotic properties, up to 90% of antibiotics pass un-degraded through animals to feces. Further, during rain events, constituents of land applied-manure, such as nutrients, antibiotics, and antibiotic resistant bacteria have the potential to be directly transported from the soil surface to groundwater in areas overlaying karst geology. However, the extent of antibiotic resistance movement from surface water to groundwater (leachate) is unknown following poultry litter applications in karst and non-karst landscapes. To address this important research question for human and environmental health, researchers extracted large, in tact soil columns from karst and non-karst landscapes and applied poultry litter to the surface and then conducted simulated rainfall events. This study found that there was 1.5 times greater antibiotic resistant bacteria in karst groundwater compared to non-karst systems. Therefore, researchers suggest using precision nutrient application tools to avoid applying manure in karst landscapes. These findings highlight the need for spatially-driven manure nutrient management strategies for reducing antibiotic resistant dissemination in the environment.

Technical Abstract: Antibiotic resistance is increasingly recognized as a critical challenge affecting human, animal, and environmental health. Yet, environmental dynamics and transport of antibiotic resistance genes (ARGs) and microbial communities in karst and non-karst landscapes following poultry litter land applications are not well understood. This study investigates the impact of poultry litter application on the proliferation of ARGs (tetW, qnrS, ermB, sulI, and blactx-m-32), class 1 integron (intl1), and alterations in microbial communities (16S rRNA) within karst and non-karst landscapes, which are crucial and under-researched systems in the global hydrological cycle. Using large, intact soil columns (45 cm diam. × 100-cm height) from karst and non-karst landscapes, the role of preferential flow and ARG transport in leachate was enumerated following surface applied poultry litter and simulated rain events. This research demonstrated that in poultry litter amended karst soils, ARGs (i.e., ermB and tetW) abundance increased 1.5 times compared to non-karst systems (p <0.05), highlighting the influence of geological factors on ARG proliferation. Notably, microbial communities in karst leachate exhibited increased diversity and abundance, suggesting a potential linkage between microbial composition and ARG presence. Further, our correlation and network analyses delineated distinct relationships between leachate ARGs, microbial taxa, and physicochemical properties, underscoring the complex interplay in these environmentally sensitive areas. These findings illuminate the critical role of karst landscape in shaping ARG abundance and pollutant dispersal, and linkages to microbial communities, thus emphasizing the need for landscape-specific approaches in managing ARG dissemination to the environment. Our study not only contributes to a deeper understanding of hydrogeological ARG dynamics but also lays the groundwork for future research and targeted strategies to spatially mitigate ARG dissemination across agricultural landscapes.