Journal: Frontiers in Microbiology

Article Title: Postbiotic sequestration of micro- and nanoplastics: in vitro intestinal epithelial protection and proof of concept in the human mouth

doi: 10.3389/fmicb.2026.1881786

Figure Lengend Snippet: Experimental framework for evaluating Qi601 postbiotic-mediated sequestration of micro- and nanoplastics. Qi601 interactions with fluorescent polystyrene nanoplastics (PSNPs) were evaluated using a sequestration assay based on residual supernatant fluorescence. The Qi601–PSNP system was then subjected to sequential simulated salivary, gastric, and intestinal digestion. Caco-2 assays examined PSNP association with epithelial cells during co-exposure with Qi601, after PSNP pre-exposure followed by Qi601 treatment, and after exposure to preformed Qi601–PSNP aggregates to assess transfer to the apical cell surface. Fluorescence microscopy, confocal microscopy, scanning electron microscopy, and atomic force microscopy were used to examine PSNP–cell interactions and Qi601-associated particle aggregates. An oral chewing-gum proof-of-concept experiment was used to collect saliva samples for fluorescence microscopy and LDIR analysis of gum-derived microplastic particles. Created with BioRender.com .

Article Snippet: Caco-2 cells (ATCC HTB-37; American Type Culture Collection, Manassas, VA, USA; RRID: CVCL_0025HTB-37) were used for in vitro PSNP uptake experiments.

Techniques: Fluorescence, Microscopy, Confocal, Scanning Electron Microscopy, Analysis, Derivative Assay, Microplastic

Journal: Frontiers in Microbiology

Article Title: Postbiotic sequestration of micro- and nanoplastics: in vitro intestinal epithelial protection and proof of concept in the human mouth

doi: 10.3389/fmicb.2026.1881786

Figure Lengend Snippet: Post-exposure Qi601 reduces epithelial PSNP burden. Caco-2 monolayers were exposed to PSNPs for 24 h and treated with Qi601 at 3 mg/mL or control medium for 5 or 24 h. For fluorometric assays, fluorescence was normalized to the protein content of each well and expressed as RFU/μg protein. (A) Surface-associated PSNP fluorescence after 5 h of Qi601 treatment ( n = 3 biological replicates, comprised of 3 technical replicates per group). (B) Intracellular PSNP fluorescence after 5 h of Qi601 treatment ( n = 3 biological replicates, comprised of 3 technical replicates per group). (C) Surface-associated PSNP fluorescence after 24 h of Qi601 treatment ( n = 5 biological replicates, comprised of 3 technical replicates per group). (D) Intracellular PSNP fluorescence after 24 h of Qi601 treatment ( n = 5 biological replicates, comprised of 3 technical replicates per group). (E) Confocal z-stack analysis of surface-associated PSNP fluorescence after 5 and 24 h of Qi601 treatment ( n = 3 biological replicates, comprised of 14 ROIs). (F) Confocal z-stack analysis of intracellular PSNP fluorescence after 5 and 24 h of Qi601 treatment ( n = 3 biological replicates, comprised of 14 ROIs). Data are presented as mean ± SD. RFU, relative fluorescence units. * p < 0.05; ** p < 0.01; *** p < 0.001.

Article Snippet: Caco-2 cells (ATCC HTB-37; American Type Culture Collection, Manassas, VA, USA; RRID: CVCL_0025HTB-37) were used for in vitro PSNP uptake experiments.

Techniques: Control, Fluorescence, Confocal, Analysis

Journal: Frontiers in Microbiology

Article Title: Postbiotic sequestration of micro- and nanoplastics: in vitro intestinal epithelial protection and proof of concept in the human mouth

doi: 10.3389/fmicb.2026.1881786

Figure Lengend Snippet: Post-exposure Qi601 treatment reduces cell-localized PSNP fluorescence. Cell-localized PSNP fluorescence was quantified within the entire cellular region of interest (ROI) (A) , cytoplasmic ROI (B) , and perinuclear ROI (C) at 5 h and 24 h after Qi601 treatment ( n = 3 biological replicates; 14–20 ROI technical replicates analyzed per condition). Representative confocal images of Caco-2 monolayers exposed to PSNPs for 24 h without (D) or with (E) Qi601. Left panels show the analyzed fields; enlarged regions and orthogonal z-stack views are shown on the right. PSNPs are green, F-actin is red, and nuclei are blue. PSNP fluorescence was quantified as the integrated fluorescence intensity of PSNP-positive pixels within each ROI. Data are presented as mean ± SD. * p < 0.05, ** p < 0.01, *** p < 0.001.

Article Snippet: Caco-2 cells (ATCC HTB-37; American Type Culture Collection, Manassas, VA, USA; RRID: CVCL_0025HTB-37) were used for in vitro PSNP uptake experiments.

Techniques: Fluorescence, Confocal

Journal: Frontiers in Microbiology

Article Title: Postbiotic sequestration of micro- and nanoplastics: in vitro intestinal epithelial protection and proof of concept in the human mouth

doi: 10.3389/fmicb.2026.1881786

Figure Lengend Snippet: Qi601 reduces PSNP–epithelial association with minimal transfer of Qi601-sequestered PSNPs to cells. (A, B) Protection assay. Caco-2 monolayers were pretreated with Qi601 (3 mg/mL) before PSNP exposure. Surface-associated (A) and intracellular (B) PSNP fluorescence were measured at 5 and 24 h. (C-F) Transfer assay. Pre-formed Qi601-PSNP agglomerates (QPAs) were applied to Caco-2 monolayers. Surface-associated PSNP fluorescence was measured after 5 h (C) and 24 h (D) , and intracellular PSNP fluorescence after 5 h (E) and 24 h (F) , across PSNP concentrations of 0.1–2.5%, and compared with PSNP-only controls. (G) Percentage of Qi601-associated PSNP fluorescence transferred to Caco-2 monolayers at 5 and 24 h. Experiments included n = 3 biological replicates, each comprising 3 technical replicates. Fluorescence (RFU) was normalized to protein content per well. Data are presented as mean ± SD. RFU, relative fluorescence units. * p < 0.05, ** p < 0.01, *** p < 0.001.

Article Snippet: Caco-2 cells (ATCC HTB-37; American Type Culture Collection, Manassas, VA, USA; RRID: CVCL_0025HTB-37) were used for in vitro PSNP uptake experiments.

Techniques: Fluorescence

Journal: Frontiers in Microbiology

Article Title: Postbiotic sequestration of micro- and nanoplastics: in vitro intestinal epithelial protection and proof of concept in the human mouth

doi: 10.3389/fmicb.2026.1881786

Figure Lengend Snippet: Multimodal imaging demonstrates extracellular association of PSNPs with Qi601 aggregates. (A) Fluorescence microscopy shows concentrated PSNP fluorescence in discrete Qi601 assemblies. (B) AFM phase images show PSNPs surrounding and on Qi601 surfaces (i), Qi601-only (ii) and PSNP-only controls (iii). (C i-iv) Confocal microscopy localizes Qi601-PSNP agglomerates (QPAs) above the Caco-2 monolayer. Caco-2 monolayers (i) show uptake of PSNPs. Qi601 aggregates (ii, iii) remain above the monolayer and accumulate PSNPs (iv) . Orthogonal z-stack views demonstrate separation between the aggregates (outlined in white) and the underlying cells, with multiple PSNP foci localized in smaller Qi601 assemblies. (D) SEM shows numerous PSNPs clustered on or within Qi601 aggregates on the Caco-2 epithelial surface. Higher magnification reveals PSNPs embedded in a mesh-like Qi601-associated matrix and closely apposed to Qi601 surfaces. (E) In the absence of Qi601, PSNPs adhere to Caco-2 cell microvilli. Scale bars are shown in each panel.

Article Snippet: Caco-2 cells (ATCC HTB-37; American Type Culture Collection, Manassas, VA, USA; RRID: CVCL_0025HTB-37) were used for in vitro PSNP uptake experiments.

Techniques: Imaging, Fluorescence, Microscopy, Confocal