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

Abstract

Metal(loid)s can increase the spread and enrichment of antibiotic resistance in the environmental system by means of a co-selection effect. The effects of introducing antibiotics into the environment on the long-term resistance of microbial communities to metal(loid)s are largely unknown. Here, manure-fertilizers that contained either oxytetracycline (OTC) or sulfadiazine (SD) at four concentrations (0, 1, 10, and 100 mg kg⁻¹) were incorporated into a maize cropping system in an area with a high arsenic geological background. The results showed that the introduction of exogenous antibiotics had a notable effect on the bacterial diversity of the maize rhizosphere soil, as evidenced by alterations in Chao1 and Shannon index values when compared to those of the control. Oxytetracycline exposure did not significantly alter the prevalence of most bacterial phyla, with the exception of Actinobacteria. However, sulfadiazine antibiotic exposure caused a decrease in prevalence as exposure concentrations increased, with the exception of Gemmatimonadetes. The same reaction pattern was observed in the five most prevalent genera, such as Gemmatimonas, Fulvimonas, Luteimonas, Massilia, and Streptomyces. It was observed that the abundance of tetC, tetG, and sul2 antibiotic resistance genes (ARGs) significantly increased in correlation with the concentration of antibiotic exposure, and a strong link was found between these genes and integrons (intl1). The abundance of microbial functional genes related to arsenic transformation (aioA and arsM) increased when there was an increase in oxytetracycline exposure concentrations, whereas a decrease in abundance was observed with increasing sulfadiazine exposure concentrations. Proteobacteria, Actinobacteriota, Acidobacteriota, Chloroflexi, Firmicutes, Bacteroidota, Gemmatimonadota, Cyanobacteria and Planctomycetes were found to be important indicators of the introduction of antibiotics, and may be essential in the development of antibiotic resistance in soils with high arsenic geological background. Planctomycetacia (from Planctomycetes) was significantly negatively correlated with sul2 and intl1 genes, which might play a role in the development of resistance profiles to exogenous antibiotics. This study will expand our understanding of microbial resistance to antibiotic contamination in areas with a high geological background, as well as reveal the hidden ecological effects of combined contamination.