Background: Polyvinyl chloride (PVC) is one of the most widely used synthetic polymers globally, and its continuous accumulation in natural ecosystems has emerged as a critical environmental and public health concern. Recently, microbial degradation has been recognized as an efficient and eco-friendly strategy for mitigating plastic pollution. Despite increasing interest, knowledge of bacteria capable of efficiently degrading PVC microplastics (PVC-MPs) remains limited. This gap highlights the urgency of exploring novel bacterial candidates for effective PVC biodegradation. Methodology: In this study, soil samples collected from plastic-contaminated sites were utilized to isolate PVC-degrading bacteria using enrichment culture techniques. Bacterial isolates showing potential interaction with PVC were selected and molecularly identified. In addition, their efficacy in degrading PVC-MPs was further confirmed through a combination of analytical and spectroscopic techniques, including scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and gas chromatography–mass spectrometry (GC–MS). Results: The two isolates identified as Stutzerimonas sp. NH2 and Glutamicibacter nicotinae NH27 displayed markedly different PVC biodegradation efficiencies. Strain NH2 achieved a PVC-MPs weight loss of 23.41 ± 0.93%, whereas strain NH27 exhibited a lower degradation efficiency of 5.87 ± 2.16%. Notably, the consortium composed of both strains in equal volumes resulted in a greater PVC-MPs weight loss of 26.84 ± 0.94%, representing a significant increase in PVC-MPs degradation compared with each strain alone ( p < 0.05). SEM analysis revealed pronounced morphological alterations on PVC surfaces following bacterial exposure, including cracks, fissures, and grooves. FTIR spectra demonstrated a substantial reduction in the intensities of some functional groups, which could be attributed to PVC degradation. TGA analysis showed a measurable decline in thermal stability, further suggesting chemical structural modifications due to bacterial activity. Additionally, GC–MS analysis detected potential degradation products, providing clear chemical evidence of bacterial-driven PVC degradation. Conclusion: This study reports, for the first time, the potential involvement of Stutzerimonas sp. NH2 and Glutamicibacter nicotinae NH27 in the transformation of PVC microplastics. The findings also provide initial insights into the combined activity of these two strains on PVC-MPs, supported by multiple physicochemical analyses. These results contribute to the growing understanding of microbial interactions with PVC microplastics and highlight the potential of these bacteria for future bioremediation studies. Graphical

Background: Oils from medicinal plants, including thyme (Thymus vulgaris), cinnamon (Cinnamomum verum), and black seed (Nigella sativa), are recognized for their antibacterial and antioxidant properties. While several studies have investigated individual oils and binary combinations, fewer reports have examined ternary mixtures using systematic optimization approaches. Accordingly, the present study aimed to optimize the antibacterial and antioxidant performance of combinations of these three plant-derived oils using a statistical mixture design strategy supported by in silico exploration. Methods: An Augmented Simplex Centroid Mixture Design was applied to evaluate the individual and combined effects of thyme, cinnamon, and black seed oils. Antibacterial activity was assessed by determining the minimum inhibitory concentrations (MICs) against Escherichia coli and Staphylococcus aureus, while antioxidant activity was measured using the DPPH radical scavenging assay (IC₅₀). The experimental data were fitted to a special cubic model, and model validity was verified through ANOVA parameters, including F-values, R², and adjusted R². Multi-response optimization was performed using a desirability function. Potential interactions among oils were further examined using checkerboard assays. Molecular docking and ADMET predictions were conducted as supportive, hypothesis-generating tools. Results: The special cubic model was statistically significant for all responses (p < 0.0001), with R² values of 0.9763, 0.9944, and 0.9841 for MIC_{E. coli}, MIC_{S. aureus}, and DPPH IC₅₀, respectively. Response surface analysis and multi-response optimization identified the optimal oil mixture as thyme (41.7%), cinnamon (41.7%), and black seed (16.7%), achieving MIC values of 0.5 µL/mL for E. coli and 0.517 µL/mL for S. aureus, and a DPPH IC₅₀ of 5.32 ± 0.52 mg/mL. Checkerboard assays confirmed synergistic interactions for the optimized formulation, with ΣFIC values of 0.15 and 0.29 against E. coli and S. aureus, respectively. Cytotoxicity testing of the optimized formulation on WI-38 normal fibroblasts indicated high cell viability (>92%) at all tested concentrations. In silico docking showed favorable binding affinities of major oil constituents with bacterial targets, and ADMET analysis suggested acceptable pharmacokinetic and safety profiles. Conclusions: The study demonstrated that specific combinations of thyme, cinnamon, and black seed oils can synergistically enhance antibacterial and antioxidant activities. The optimized formulation exhibited enhanced antibacterial and antioxidant activities with minimal cytotoxicity, while in silico analyses provided supportive mechanistic insights.