Grazing of ciliated protozoa on free and particle-attached bacteria

Abstract

The grazing preference of natural assemblages and of isolated species of ciliated protozoa for free or for particle-attached bacteria was tested. Bacterivorous ciliates were obtained from tidal creek water and from the surface flocculent layer of Spartina salt marsh sediments. Free and particle-attached bacteria were prepared by growing a Gram-negative, rod-shaped bacterium either in a nutrient solution, or on the surfaces of artificially made alginate beads containing the same nutrients. The free and particle-attached bacteria were stained with a fluorescent dye and offered separately to ciliates in trace amounts. Uptake of fluorescently labeled bacteria by ciliates was monitored over 30 to 60 min periods. All ciliates tested, except for a Euplotes sp. isolated from marsh floc, fed equally well or better on free FLG than on attached FLB.