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Oxygen Perception and O 2 Toxicity in the Freshwater Ciliated Protozoon Loxodes
Author(s) -
FINLAY B. J.,
FENCHEL T.,
GARDENER S.
Publication year - 1986
Publication title -
the journal of protozoology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.067
H-Index - 77
eISSN - 1550-7408
pISSN - 0022-3921
DOI - 10.1111/j.1550-7408.1986.tb05582.x
Subject(s) - oxygen , anoxic waters , sodium azide , catalase , chemistry , antimycin a , hydrogen peroxide , superoxide dismutase , cytochrome c oxidase , biophysics , environmental chemistry , biochemistry , biology , electron transport chain , oxidative stress , mitochondrion , organic chemistry
.Loxodes reached peak abundance close to the oxic‐anoxic boundary (O 2 5% atm) in two lakes, in test tube cultures, and in glass chambers with horizontal O 2 gradients. Vertical profiles of CO 2 , pH, sulfide, and Fe 2+ in a lake were not closely related to Loxodes abundance. In a laboratory experiment, Loxodes followed a retreating source of O 2 and was repelled by a high pO 2 . This behavior was sustained when cells simultaneously swam up or down gradients of both CO 2 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 (O ‐ 2 ) and hydrogen peroxide (H 2 O 2 ) were probably not responsible for the exclusion of Loxodes from water with a high pO 2 . Continuous exposure of Loxodes to oxygen at normal atmospheric pressure at 10°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 O 2 . Behavioral responses to the dissolved oxygen tension probably controlled the spatial distribution of Loxodes.