Ref ID : 1061
L.J. Albright, Evelyn B. Sherr, and R.D. Fallon; Grazing of ciliated protozoa on free and particle-attached bacteria. Mar.Ecol.Prog.Ser. 38:125-129, 1987
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We tested the grazing preference of natural assemblages and of isolated species of ciliated protozoa for free of for particle-attached bacteria. 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 (5% of the natural bacterial abundance of 10E6 to 10E7 cells ml-1). Uptake of fluorescently labeled bacteria (FLB) by ciliates was monitored over 30 to 60 min periods. All ciliates tested, except for an Euplotes sp. isolated from marsh floc, fed equally well or better on free FLB than on attached FLB. The marsh floc ciliates showed a stronger preference for attached bacteria then did tidal creek ciliates. Small spirotorichous ciliates and a free-swimming peritrich present in creek water ingested free FLB at rates 12 to 36 times greater than found for attached FLB. Our experimental results indicate that bacterivorous ciliates are capable of feeding on free bacteria at bacterial abundances less than 10E7 cells/ml, and may not, as presently thought, be confined to grazing attached or aggregated bacteria in natural waters.