Polystyrene and polytetrafluoroethylene nanoplastics affect probiotic bacterial characteristics and penetrate their cellular membrane

One of the main targets of nanoplastic (NP) toxicity is thegastrointestinal tract, where the gut microbiota acts as a crucialbiological barrier, by regulating nutrient and energy metabolism andmaintaining the immune defence system. Lactic acid bacteria (LAB) arekey components of the human intestinal microbiota and include many ofthe most important health-promoting probiotic strains. It has beenproposed that specific LAB strains can protect against human toxicitycaused by polystyrene (PS) NPs. Despite these findings, it is still notcompletely clear how the physiology and functional traits of LAB areinfluenced by NPs. In this study, we report how PS andpolytetrafluoroethylene NPs, having significantly different chemicalcompositions, affect the key surface-associated phenotypic traits ofselected LAB and penetrate their cellular membranes. Here, we show thatNPs, particularly PS-NPs, significantly affect the hydrophobicity andauto-aggregation of the bacterial strains, in a species- andstrain-dependent manner. PS-NP exposure resulted in a marked reductionin surface hydrophobicity and, in most cases, a concomitant increase inauto-aggregation; notably, Bifidobacterium breve Reuter exhibited thehighest sensitivity to PS-NPs. Accordingly, membrane permeability assaysand TEM analysis revealed substantial loss of cell wall integrity andconsequent internalization of PS-NPs by the bacterial cells. In terms oflifestyle transitions, PS-NP exposure promoted a shift from planktonicto biofilm-associated growth in LAB strains. Overall, these findingshighlight the disruptive potential of NPs on bacterial physiology andviability, with implications for gut microbiota stability and probioticefficacy. The differential responses observed emphasize the importanceof strain-specific assessments when evaluating NP toxicity.