title: Nitrate reductase activity, ammonium regeneration, and orthophosphate uptake in protozoa isolated from Lake Kinneret, Israel.
abstract: Nitrate reductase (NR) activity and nutrient (N, P) recycling in the ciliatesColpoda steinii andStylonychia sp. and two unidentified flagellates (I and II), isolated from Lake Kinneret, have been studied. When grown on a bacterium also isolated from the lake, all species, except flagellate I, exhibited NR activity. Activity was higher in the presence of nitrate than in its absence, and in the case ofC. steinii showed a dependence on initial ambient NO3 concentrations in the cultures. NR activity was inversely proportional to body size, suggesting that the larger protozoan species have decreased specific metabolic rates. A net increase in ammonium concentrations and a decrease in orthophosphate levels was observed, but both phenomena were much less sensitive to ambient NO3 concentrations than NR activity. Similar trends in NR activity and NH4 production were also observed whenC. steinii was grown on the picocyanobacteriumSynechococcus sp. Our results suggest that NH4 excretion is the outcome of N remineralization from the food supply but is also partially due to dissimilatory nitrate reduction. These data imply that protozoa may have an important role in nutrient recycling in Lake Kinneret and that some species could use NO3 respiration in anoxic regions of the water column.
authors.affiliation: Israel Oceanographic and Limnological Research, Kinneret Limnological Laboratory, P.O. Box 345, 14102, Tiberias, Israel.
authors.forename: O
authors.initials: O
authors.lastname: Hadas
authors.forename: R
authors.initials: R
authors.lastname: Pinkas
authors.forename: D
authors.initials: D
authors.lastname: Wynne