Experimental approach to the role of protozoa in aquatic ecosystems

Abstract

In enrichment batch experiments, samples from three water bodies were alternatively supplemented by various amounts of organic material and incubated at 20 C. Colpidium campylum reached its highest total cell volumes in cultures with the highest initial total cell volumes in cultures with the highest initial concentrations of organics; Cyclidium glaucoma preferred lower concentrations; and Glaucoma chattoni occupied the intermediate position. None of the species preferred any special type of organic material. In two-stage continuous-flow units, a mixed culture of bacteria was kept in stage I and the clones of ciliates were maintained in stage II. The interrelations between the total cell volumes of ciliates at various concentrations of bactopeptone were in accordance with the results from the enrichment experiments. Since the growth of bacteria continued in the presence of ciliates, a four-stage apparatus was constructed in which a bacterial culture was raised and diluted in three stages before entering the culture ofColpidium. The bacterial growth in the presence of Colpidium was not eliminated even by this arrangement, as demonstrated by dosing antibiotics along with bacteria. An effect of ciliate metabolites on bacterial growth rate is suggested, completing a metabolic cycle in the bacteria-protozoa system. © 1973 by the American Society of Zoologists.