Extracellular polymeric substances are the sticky mixture of sugars, proteins and other molecules that bacteria secrete around themselves. It is what holds a biofilm together, and it is also the layer that does much of the catching when a bacterial surface binds something from its surroundings.
Drawn from background microbiology, not from this paper.
The authors point out that the question of whether plastics harm the beneficial organisms already living in the gut has gone largely unexamined, even as the evidence of harm to the host has grown. They set out to establish whether ingested particles cause physiological toxicity to intestinal probiotics and, if so, by what route.
Drawn from the paper's introduction.
In a system simulating digestion, micro and nanoplastics inhibited the growth of Lacticaseibacillus rhamnosus and suppressed both its lactic acid output and its secreted polymer layer.
The toxicity depended on which plastic it was. Polyethylene terephthalate was worse than polystyrene, which was worse than polyvinyl chloride. Nanoscale particles were worse than larger ones, and higher concentrations were worse than lower.
Under the harshest condition tested, 150 nanometre digested polyethylene terephthalate at 250 milligrams per litre, electron microscopy showed the secreted polymer layer binding to the particles and then adhering back onto the bacterial surface, which the authors read as physical obstruction and membrane damage.
Transcriptomics and metabolomics together showed core genes strongly down regulated, galK at a log2 fold change of minus 5.40 and bglA at minus 6.58, with reduced metabolites across the phosphotransferase system, glycolysis, the citric acid cycle, the pentose phosphate pathway and oxidative phosphorylation.
Adding glucose back partly restored function, but the upstream metabolic damage persisted.
| Toxicity ranking by polymer | polyethylene terephthalate worse than polystyrene, worse than polyvinyl chloride |
| Harshest condition tested | 150 nanometre digested polyethylene terephthalate at 250 milligrams per litre |
| Gene down regulation | galK log2 fold change minus 5.40, bglA minus 6.58 |
| Pathways affected | phosphotransferase system, glycolysis, citric acid cycle, pentose phosphate pathway, oxidative phosphorylation |
| Glucose rescue | partial restoration of function, upstream damage persisted |
Shown in this study The study measured this step directly.
The damage starts at the front door. Genes for taking sugar into the cell and breaking it down were strongly suppressed, and the metabolites downstream of them fell across every central pathway measured, which starves the cell of both energy and the building blocks it needs.
That is why the secreted layer and the lactic acid both fall. Neither can be made without precursors, so a supply problem upstream shows up as two missing products downstream.
The microscopy adds a second insult on top of the first. The layer the organism secretes binds the particles and then sits back down on the cell surface, which the authors read as physical obstruction and membrane damage rather than a chemical effect.
The glucose experiment locates the injury. Feeding the cell sugar directly recovered some function, so part of the problem is supply, but the upstream damage did not repair, so the rest of it is not.
Drawn from the paper's transcriptomics, metabolomics and electron microscopy.
The organism proposed as the tool is also a target. Binding plastic is not a free action for the bacterium doing it, and the same stickiness that makes a strain useful is what fouls its own surface.
One probiotic species in a simulated digestion vessel, at concentrations chosen to produce measurable effects.
Running the same measurements on the strains selected elsewhere for high binding capacity, which would show whether the best binders pay the highest price.
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