Food bacteria and synthetic microparticles of similar size influence pharyngeal pumping of Caenorhabditis elegans

Highlights: • Pharyngeal pumping is an important indicator for food ingestion by nematodes. • Size and shape of synthetic beads were already important triggers for pumping. • Item presence and their nutritional value determined pumping rates. • At quantities >10⁷ items ml^–1, nutritional value became more essential for pumping. • Low-frequency pumping at bead exposure prevent the nematodes from wasting energy. Toxicity tests using the model organism Caenorhabditis elegans have shown that exposure to small microplastics such as polystyrene (PS) beads lead to high body burdens and dietary restrictions that in turn inhibit reproduction. Pharyngeal pumping is the key mechanism of C. elegans for governing the uptake of food and other particles and can be easily monitored by determining the pumping rates. In this study, pharyngeal pumping of C. elegans was examined in response to increasing quantities of food bacteria (E. coli: 10⁶–10¹⁰ cells ml^–1) and synthetic particles (10⁷–10⁹ beads ml^–1) of similar size (1 µm). While the average pumping rate of C. elegans exposed to E. coli depended on the density of the bacterial cells, this was not the case for the synthetic beads. At 10⁷ items ml⁻¹, bacterial cells and synthetic beads triggered a basic stimulation of the pumping rate, independent of the nutritional value of the particle. At quantities >10⁷ items ml^–1, however, the nutritional value was essential to maximize the pumping rate, as it was upregulated only by E. coli cells, which can be chemosensorially recognized by C. elegans. Given the unselective uptake of all particles in the size range of bacteria, restricting the pumping rates for particles with low nutritional value to a basic rate, prevents the nematodes from wasting energy by high-frequency pumping, but still allows a food-quality screening at low food levels.