Enrichment of endophytic Actinobacteria in roots and rhizomes of Miscanthus × giganteus plants exposed to diclofenac and sulfamethoxazole

This study investigates how wastewater containing 2 mg l⁻¹ of sulfamethoxazole (SMX) and 2 mg l⁻¹ of diclofenac (DCF) affects the composition of bacterial communities present in the roots and rhizomes of Miscanthus × giganteus plants grown in laboratory-scale constructed wetlands. Bacterial communities in plant roots and rhizomes were identified in treated and control samples by 16S rRNA amplicon sequencing. Moreover, bacterial endophytes were isolated in R2A and 1/10 869 media and screened for their ability to metabolize SMX and DCF in liquid medium by HPLC. Our results show significant changes in the abundance of main genera, namely Sphingobium and Streptomyces between control and treated plants. Around 70% of the strains isolated from exposed plants belonged to the phylum Actinobacteria and were classified as Streptomyces, Microbacterium, and Glycomyces. In non-exposed plants, Proteobacteria represented 43.5% to 63.6% of the total. We identified 17 strains able to remove SMX and DCF in vitro. From those, 76% were isolated from exposed plants. Classified mainly as Streptomyces, they showed the highest SMX (33%) and DCF (41%) removal efficiency. These isolates, alone or in combination, might be used as bio-inoculants in constructed wetlands to enhance the phytoremediation of SMX and DCF during wastewater treatment.