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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Loxodes

The genus Loxodes seek out and tend to congregate in microaerobic environments (pO2 ~5% atm) such as the lower part of the oxycline in stratified lakes. This behavior depends on three different types of resposne to oxygen. (1) A transient phobic response ("avoidance reaction") is observed when cells enter a higher O2 tension. (2) A kinetic response; in suboptimal O2 tensions (anoxic or >10% atm) cells increase their motility by swimming faster and by reducing the frequency of tumbling whereas motility becomes minimal at the optimum pO2. (3) The pO2 of the medium modifies a true mechanoreceptor-mediated geotaxis; in anoxia the cells tend to swim vertically upwards and at high O2 tensions (>10% atm) they swim downwards. This taxis is only functional in vertical O2 gradients whereas the phobic and kinetic responses allow orientation in horizontal gradient. Loxodes also reacts to light. The effect of light is to amplify the sensitivity to O2 and Loxodes responds to a high light level by seeking out a lower O2 tension. (ref. ID; 500)

Loxodes striatus

[ref. ID; 500]

Test system

Oxygen perception and O2 toxicity

Strains

From Esthwaite Water and Priest Pot (Cumbria, U.K.). Food: Axenic Astasia longa (CCAP 1204/17A).

Toxicants/concentrations

Antimycin A/10E-3 ~ 10E-5 M, 2,4-Dinitrophenol (2,4-DNP)/10E-3 ~ 10E-4 M, 2-Heptyl-4-hydroxyquinoline-N-oxide (HOQNO)/10E-4 ~ 10E-6 M, Potassium cyanide (KCN)/10E-2 ~ 10E-6 M, Rotenone/10E-3 ~ 10E-5 M, and Sodium azide (NaN3)/10E-1 ~ 10E-4 M.

Test design

Test vessel (tubes or petri dishes). Light levels (dark, 500, and 1250 uE m-2sec-1).

Measurements

Swimming tracks. Survival number(%). Activities of superoxide dismutase (SOD) and catalase (CAT).

[ref. ID; 6111]

Test system

Acute toxicity (24-hr LC50)

Strains

The organisms was obtained, initially, from Stirone Stream (northern Italy), a freshwater environment free from known toxicants and, in particular, from heavy metals. The culture medium was constituted of boiled rice and wheat grain in 10 ml of filtered natural water. 20+/-1 degrees C, photoperiod of 16:8 hr light:dark.

Toxicant/concentrations

NiCl2/6H2O (1.5, 1.6, 1.8, 2 ppm).

Test design

Tissue culture plates with 24 wells, 3 replicates.

Measurements

Mortality or the survivorship.

Evaluations

LC50 using the probit method.