Ref ID : 500
Bland J. Finlay, Tom Fenchel, and S. Gardener; Oxygen perception and O2 toxicity in the freshwater ciliated protozoon Loxodes. J.Protozool. 33(2):157-165, 1986
Reprint
In File
Notes
Loxodes reached peak abundance close to the oxic-anoxic boudary (O2 <5% atm) in two lakes, in test tube cultures, and glass chambers with horizontal O2 gradients. Vertical profiles of CO2, pH, sulfide, and Fe2+ in a lake were not closely related to Loxodes abundance. In a laboratory experiment, Loxodes followed a retreating souce of O2 and was repelled by a high pO2. This behavior was sustained when cells simultaneously swam up or down gradients of both CO2 and pH. Aggregation of cells was abolished by KCN (10(-4) - 10(-6) M). Sodium azide (10(-1) - 10(-4) M) had no effect and 2,4-DNP sharpened the aggregation. Rotenone, Antimycin A, and HOQNO had no obvious effect. Cytochrome oxidase is probably the oxygen receptor. Loxodes striatus contained low activities of superoxide dismutase and catalase. Extracellular production of superoxide (O2-) and hydrogen peroxide (H2O2) were probably not responsible for the exclusion of Loxodes from water with a high pO2. Continuous exposure of Loxodes to oxygen at normal atmospheric pressure at 10 degrees C led to 50% mortality in 10 days. Cells left free to swim in an oxygen gradient doubled their number in the same period. Light exacerbated the toxic effects of O2. Behavioral responses to the dissolved oxygen tension probably controlled the spatial distribution of Loxodes.