Combined Effects of Ciprofloxacin and Microplastics on Alpine Spring Water Microbiota: Evidence from Glacier-Fed Microcosm Experiments

Domenica Mosca Angelucci¹Federica Piergiacomo²Enrica Donati³Leonardo Pagani⁴Elisa Minuti²Lorenzo Brusetti^2*Maria Concetta Tomei¹

• ¹Istituto di Ricerca sulle Acque Consiglio Nazionale delle Ricerche, Rome, Italy
• ²Free University of Bozen-Bolzano, Bolzano, Italy
• ³Istituto per i Sistemi Biologici Consiglio Nazionale delle Ricerche, Montelibretti, Italy
• ⁴Ospedale di Bolzano, Bolzano, Italy

microbial compositional shifts, favoring known CIP-degrading taxa. A shared core microbiome of 216 amplicon sequence variants was detected across all conditions, but specific taxa were differentially enriched under varying exposures. The combined CIP+PET test induced the strongest community shifts, while CIP alone shared fewer taxa with controls, indicating selective pressure for resistant microorganisms like Achromobacter. PET MPs also shaped distinct microbial assemblages, possibly by offering niches favoring biofilm-associated genera such as Luteolibacter. Biodiversity metrics showed highest richness and evenness in CIP-free conditions (Control and PET), while CIP significantly reduced alpha diversity, favouring resistant taxa, as confirmed by NMDS and lower Shannon and Simpson indices. Effects of MPs were still noticeable.Conclusions: These findings demonstrate the disruptive effects of CIP on alpine freshwater microbial communities and highlight the additional, though more moderate, influence of MPs.The combined presence of MPs and antibiotics may exacerbate resistance spreading by enhancing persistence and providing favorable conditions for resistant biofilms. A mechanistic understanding of these interactions is essential for accurate risk assessment and the development of effective mitigation strategies in alpine and other vulnerable freshwater ecosystems.