Ref ID : 1642
B.J. Finlay; Nitrate respiration by Protozoa (Loxodes spp.) in the hypolimnetic nitrite maximum of a productive freshwater pond. Freshwater Biology 15:333-346, 1985
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1. The ciliated protozoon Loxodes dominated the microfaunal community living in the anoxic hypolimnion of Priest Pot, a small productive pond. Its peak abundance close to the oxic-anoxic boundary was always associated with a peak in nitrite (NO2-) concentration. Both peaks were usually found in water containing <1 µmolO2 L-1. 2. The microfauna were concentrated on a 30 µm sieve. The number of Loxodes in the sieve retentate correlated well with the activity of nitrate reductase in the same material, implying that the enzyme was located in Loxodes. It is unlikely that residual bacterial contamination could have accounted for the activity. 3. A doubling of specific electron transport system activity was associated with the transition across the oxic-anoxic boundary. This is consistent with the switch to nitrate respiration and the lower energy yield it provides. 4. Dissimilatory nitrate reduction was deduced to be the source of the nitrite peak. Nitrate was supplied by both run-off and nitrification. 5. It is suggested that Loxodes participates in the dissimilatory sequence of a condensed nitrogen cycle functioning across the oxic-anoxic boundary.