Effects of Inorganic Fluoride and the Fluoroquinolone Antibiotic Pefloxacin on the Growth and Microbiome Structure of Eruca sativa L.

Environmental contamination with fluorinated compounds has increased markedly due to their widespread use in industry, medicine, and agriculture. Fluoride ions and fluoroquinolone antibiotics may enter soils through fertilizers, wastewater, and manure application, where they can interact with plant-associated microbial communities. In the present study, we investigated the effects of inorganic fluoride (applied as sodium fluoride, NaF) and the fluoroquinolone antibiotic pefloxacin on the growth and microbiome composition of Eruca sativa L. Plants were cultivated under controlled conditions and exposed for four weeks to NaF or pefloxacin at equimolar concentrations of 10 and 20 µM/kg soil. Morphological parameters, including biomass accumulation, root length, leaf dimensions, and leaf area, were not significantly affected by either treatment. Nevertheless, increased variability of growth traits was observed, particularly in plants exposed to NaF. High-throughput sequencing of the 16S rRNA gene revealed pronounced, treatment-specific alterations in both rhizosphere and phyllosphere bacterial communities. The rhizosphere microbiome was relatively stable at higher taxonomic levels but exhibited selective enrichment of Actinomycetota, including the class Thermoleophilia, under NaF exposure. In contrast, the phyllosphere microbiome showed strong sensitivity to fluoride, with a marked increase in Betaproteobacteria, dominated by Burkholderiales. Changes induced by pefloxacin were weaker and more diffuse. Our results demonstrate that plant-associated microbiomes respond to fluorinated compounds at concentrations that do not induce visible plant stress. The phyllosphere microbiome, in particular, represents a sensitive indicator of fluoride exposure and may serve as an early-warning system for environmental contamination.