Biology subjects

Siebe, C.

Publications and source records attributed to Siebe, C..

3 recordsLinked to original sources

bioRxiv2026

Antimicrobial resistant bacteria in wastewater-irrigated Mexican soils and transfer of resistant bacteria from irrigated soils to cilantro plants

Agricultural fields in the Mezquital Valley, Mexico, were irrigated with untreated wastewater over several decades. Following the construction of a wastewater treatment plant (WWTP) in Atotonilco de Tula, WWTP effluent is used for irrigation. To evaluate the effects of changed irrigation, a soil incubation experiment was performed. Soils of the Mezquital Valley long-term irrigated with untreated wastewater were irrigated with WWTP influent or effluent, both unspiked and spiked with antibiotics and biocidal compounds and incubated four weeks. We investigated the effects of shifted irrigation on the abundance of cultivable total heterotrophic and resistant bacteria (RB). Additionally, RB were cultivated from Coriandrum sativum (cilantro) sown in soil of the incubation experiment. While wastewater treatment significantly reduced the bacterial abundance in effluent, spiking increased RB abundance in both wastewater types including ciprofloxacin (CIP) RB. Before wastewater addition, all soils contained cultivable RB. Irrigation increased the relative abundance of RB cultivated on Mueller Hinton (MH) agar in Leptosols and Phaeozems, compared to soils prior to wastewater addition irrespective of the water type, but not in Vertisols, suggesting the soil type rather than water qualities influenced the RB abundance. Diverse CIP RB were cultivated including strains of 14 genera of three phyla. Among those, Achromobacter spp. strains related to potentially pathogenic A. spanius originating from soil were abundant in both leaves and roots of cilantro. Our results showed that the implementation of wastewater treatment does not reduce the abundance of cultivable RB in Mezquital Valley soils and cilantro plants. Health risk associated monitoring should include long-term persistent RB colonizing plants cultivated in wastewater irrigated soils.

microbiology↗

bioRxiv2026

Wastewater and colloidal extracts of wastewater-irrigated soils select for resistant Acinetobacter baylyi beyond what measured antibiotic concentrations predict

Numerous studies have shown that the abundance of antibiotic-resistant bacteria (ARBs) or antibiotic-resistance genes (ARGs) in soil increases after irrigation with wastewater. However, it is unclear whether this increase is due to the selection effects of pharmaceutical residues in the irrigation water or the continuous introduction of ARBs and ARGs with the wastewater. Further, it is unclear how the binding of antibiotics to natural colloids (1-1000 nm) affects their biological effects compared to truly dissolved substances (< 1 nm). We conducted competition experiments with resistant and susceptible Acinetobacter baylyi BD413 strains in wastewater, as well as in colloidal and truly dissolved extracts of soils irrigated with wastewater. Although the concentrations of our six target antibiotics were far below the measured minimum selective concentrations of the tested strains, we demonstrate that the resistant strain was favored in the wastewater and the colloidal extracts. In contrast, the truly dissolved fractions exhibited weaker and more variable selective effects. A non-targeted analysis revealed the presence of 82 additional substances in our extracts, including further antibiotics, pesticides, and different non-antibiotic drugs that may influence the selection of our resistant A. baylyi BD413 strain. Our findings suggest that antibiotic resistance is selected for in wastewater and wastewater-irrigated soils. This cannot be explained by antibiotic concentrations alone, but may also arise from the effects of complex mixtures of co-occurring contaminants, particularly those associated with colloidal particles.

microbiology↗

bioRxiv2022

The global distribution and environmental drivers of the soil antibiotic resistome

BackgroundLittle is known about the global distribution and environmental drivers of key microbial functional traits such as antibiotic resistance genes (ARGs). Soils are one of Earths largest reservoirs of ARGs, which are integral for soil microbial competition, and have potential implications for plant and human health. Yet, their diversity and global patterns remain poorly described. Here, we analyzed 285 ARGs in soils from 1012 sites across all continents, and created the first global atlas with the distributions of topsoil ARGs. ResultsWe show that ARGs peaked in high latitude cold and boreal forests. Climatic seasonality and mobile genetic elements, associated with the transmission of antibiotic resistance, were also key drivers of their global distribution. Dominant ARGs were mainly related to multidrug resistance genes and efflux pump machineries. We further pinpointed the global hotspots of the diversity and proportions of soil ARGs. ConclusionsTogether, our work provides the foundation for a better understanding of the ecology and global distribution of the environmental soil antibiotic resistome.

ecology↗