Celen-Erdem, IpekHayes, Douglas G.Kalayci, SadikAcar, Ozge KarabiyikSahin, Fikrettin2026-02-152026-02-1520260964-83051879-020810.1016/j.ibiod.2026.1062912-s2.0-105028357196https://doi.org/10.1016/j.ibiod.2026.106291https://hdl.handle.net/20.500.14517/8771Polystyrene (PS) is a persistent fossil fuel-based polymer that accumulates in freshwater systems, yet its microbial degradation in such environments remains insufficiently understood. In this study, freshwater bacteria were isolated from Palando<spacing diaeresis>ken Dam (T & uuml;rkiye) and screened for their ability to degrade PS under controlled laboratory conditions. Among eleven bacterial isolates, S. marcescens V9 exhibited the highest PS degradation efficiency under laboratory freshwater conditions. Quantitative analysis showed progressive PS weight losses of 5.5 %, 6.9 %, and 13.3 % after 30, 60, and 90 days, respectively. Scanning electron microscopy (SEM) confirmed biofilm formation and surface erosion, while attenuated total reflectance-Fourier (ATR-FTIR) transform infrared and thermogravimetric analyses (TGA) indicated the formation of new oxygenated functional groups and reduced thermal stability, respectively. Gel-permeation chromatography (GPC) revealed a 28-30 % reduction in both number-and weight-average molecular weights, reflecting polymer-chain scission. Mass balance calculations suggested partial conversion of PS carbon into biomass and oxidized products, although direct CO2 evolution was not quantified and complete mineralization could not be confirmed. Collectively, these findings support an oxidative, biofilm-associated biodegradation mechanism and provide integrated evidence for PS depolymerization by a freshwater bacterial isolate, highlighting the potential role of S. marcescens V9 in environmentally relevant plastic degradation processes.eninfo:eu-repo/semantics/closedAccessPlastic PollutionMicroplastic DegradationOxidative ModificationFreshwater BacteriaBiotechnologyBiofilmArticle