Response of Antibiotic Resistance Genes and Related Microorganisms to Arsenic during Vermicomposting of Cow Dung

Abstract

Antibiotic resistance pollution in livestock manure is a persistent issue that has drawn public attention. Vermicomposting is an ecofriendly biological process that can render livestock manure harmless and resourceful. However, little is known about the impact of vermicomposting on antibiotic resistance in livestock manure under stress caused by potentially toxic arsenic levels. Herein, lab-scale vermicomposting was performed to comprehensively evaluate the shift in antibiotic resistance genes (ARGs) and related microorganisms in fresh earthworm casts as well as vermicompost product health (i.e., nutrient availability and enzyme activity) when they were fed on arsenic-contaminated cow manure. The results showed that the earthworms’ interaction with cow dung led to a significant reduction in ARG concentrations, especially for tetracycline ARGs (tet-ARGs), β-lactam ARGs (bla-ARGs), and quinolone ARGs (qnr-ARGs). However, arsenic significantly enhanced ARG accumulation in earthworm casts in a dose-dependent manner. Moreover, vermicomposting increased the percentage of Bacteroidota in the converted products. Furthermore, arsenic exposure at low concentrations promoted the proliferation of Proteobacteria, whereas high concentrations had little effect on Proteobacteria. Our study provides valuable insight into the changes in the antibiotic resistome and related microorganisms during vermicomposting of arsenic-amended cow manure, and it is crucial to explain the environmental impact of earthworms and improve our understanding of the reciprocal benefits of soil invertebrates.

Resistance profiles of microbial communities in maize rhizospheres to the introduction of exogenous antibiotics to agricultural systems with a high arsenic geological background

“…Arsenic is a naturally present element in the environment, and it is present in higher concentrations in some areas, which has led to the development of microbes that are resistant or tolerant to it. 62,64,65 In the study, the lack of significant changes in arsenic functional genes ( aioA and arsM ) in response to antibiotics entering the soil samples from the area with a high geological background may be attributed to the evolution of adaptive mechanisms, such as genes for arsenic reduction, oxidation, respiration and methylation. 27 The capability of microorganisms to thrive in arsenic-rich environments could lead to the selection of antibiotic-resistant strains or the enhancement of antibiotic resistance through a variety of co-selection processes.…”

“…22,60 Arsenic stress can cause a proliferation of antibiotic resistance genes and mobile genetic elements, thus increasing the likelihood of the dissemination of antimicrobial resistance. 61,62 This region, with its high geological background, has experienced a long-term selection pressure from arsenic, prompting the development of resistance/tolerance proles or adaptability within the soil ecosystem. The limited response of ARGs to antibiotic exposure observed in this study could be explained by the development of microbial communities' resistance/ tolerance to high levels of arsenic.…”