Effect of fixation on particle retention by microflagellates: underestimation of grazing rates
Year: 1987
Type: article
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.Recent studies of microflagellate uptake of these inert particles have yielded inconsistent results.In particular.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.We have found that a variety of flagellates egest food vacuole contents upon fixation with several commonly used agents including glutaraldehyde and formaldehyde.During time course experiments, the observed microsphere uptake rate for a small chrysomonad flagellate using 1 % glutaraldehyde was only 6 % of the rate obtained by using the fixation method of van der Veer (1982) (2 '10 acrolein, 2 % glutaraldehyde and 1 % tannic acid), modified for epifluorescence microscopy.Uptake rates of several mixed flagellate populations also were 2.4 to 3.1 times higher using the modified van der Veer method than with 1 % glutaraldehyde.The average number of ingested microspheres cell-' using this method was simllar to that observed in live cells immobilized with NiS04.Glutaraldehyde also caused the egestion of Synechococcus sp. cells and fluorescently labelled bacteria from the chrysomonad flagellate.We conclude that previous studies using common aldehyde fixation wlth particle uptake for measunng rates of microflagellate bacterivory have significantly underestimated actual rates of consumpt~on, and that these studes must be re-evaluated, and perhaps repeated, using effective fixation methods.
Source: Marine Ecology Progress Series
DOI: 10.3354/meps038251
Authors: ME Sieracki, LW Haas, DA Caron, EJ Lessard
Language: English
Domain: Life Sciences
Open Access status: bronze
Funder: National Science Foundation
OpenAlex ID: W2048477826