Fate of Protozoa transiting the digestive tract of the earthworm Lumbricus terrestris L.

In situ hybridization and subsequent epifluorescence microscopy showed that passage through the anterior part of the digestive tract (pharynx, esophagus, gizzard) of Lumbricus terrestris L. reduced numbers of protozoa indigenous to soil, shifted their cell size distribution from 3-5 mum and larger towards smaller sizes (1-3 mum), and eliminated all cells with ingested bacteria. Incubation of cast resulted in a ten-fold increase of protozoan numbers, size distribution shifts towards larger cells, and the detection of large numbers of cells with ingested bacteria (up to 46 % of the total number of cells). The suggestion that large cell sizes represented vegetative cells that were disrupted in the anterior part of the digestive tract, while small cells were cysts that passed the intestine unharmed and proliferate in cast was supported by feeding studies with vegetative cells and cysts of an Acanthamoeba sp. Vegetative cells were quantitatively disrupted in the anterior part of the digestive tract, while cysts passed through the digestive tract morphologically intact. Their failure to form vegetative cells in cast, however, suggested an additional physiological impact of passage through the digestive tract of L. terrestris on cysts of the Acanthamoeba sp.