Effect of fixation on particle retention by microflagellates: underestimation of grazing rates

Abstract

The uptake of fluorescent particles by protists and filter-feeding metazoa is being used increasingly by microbial ecologists to study feeding behavior and measure grazing rates. Grazing rates determined from fluorescent particle uptake are often less than rates measured using other techniques. These low uptake rates have been attributed to osmotrophy, food quality or size selection, rapid egestion of inert particles, and the slower feeding by free-living, as opposed to attached, protists. The average number of ingested microspheres cell using was similar to that observed in live cells immobilized with NiSO sub(4). Glutaraldehyde also cause the egestion of Synechococcus) sp. cells and fluorescently labelled bacteria from the chrysomonad flagellate.