EFFECT OF UV-B RADIATION ON CILIATED PROTOZOA - Environmental UV Radiation: Impact on Ecosystems and Human Health and Predictive Models - page 224

damage the cell 5-7 . Most of these experiments were performed by determining the UV
dose (often using UV-C wavelengths, 200-280 nm) sufficient to determine an
immobilization of the cells or a cytolysis: sometimes the minimum dose sufficient to
determine an unusual motile pattern, such as rotation, was assumed as a quantitative
assessment of cell damage. Together with these dosimetric assays, the role of
environmental conditions, such as pH or salt composition of the medium, has been
investigated.

Table 1. Resistance to UV-irradiation as a function of environment and physiological state of
different protozoa. The dose for 50% immobilization of P. multimicronucleatum was set at 100, and
the other values are relative to this (from ref. 5).

Medium or
environment

50%
rotation

50%
immobilization

50%
cytolysis

Protozoan

Balanced inorganic
salt solution

Paramecium 61 ± 6.4 100 ± 2.1

Culture medium 84 ± 2.5 114 ± 0

Distilled water 72 ± 5.6 89 ± 3.8

pH 6.0 75 ± 0 105 ± 1.8 265 ± 12

pH 7.0 65 ± 0 100 ± 0 230 ± 10

pH 8.0 50 ± 0 100 ± 0 205 ± 10

16 °C 39 ± 1.7 82 ± 3.7

19 °C 51 ± 4.5 94 ± 1

26 °C 79 ± 2.1 100 ± 1

4-day-old-culture 62 ± 4.7 100 ± 5.8 2201 ± 12.1

11-day-old-culture 48 ± 6.7 81 ± 10.0 172 ± 3.1

Blepharisma pH 6.0 82 ± 2.5 156 ± 1.8

pH 7.0 58.5 ± 7.5 101 ± 5.3

pH 8.0 54.5 ± 7.6 121 ± 5.2

Tetrahymena 1-day-old-culture in

yeast estract 146 ± 4.4

8-day-old-culture in
yeast estract 114 ± 7.0

3-day-old lettuce
culture 48.5 ± 4.2

These early studies showed that low doses of UV irradiation cause an increase in
cell speed, while, after a certain dose, the cell speed decreases, the motion pattern
becomes anomalous (cells tend to rotate around their cell body) and, eventually, cells
stop and die. Some of these results have been confirmed by our studies (see below).
The data reported in Table 1 show that the effect of UV-irradiation seems to
depend on environmental parameters, such as pH or salt concentrations. The nutritional
status and the culture age might also play a role.
The resistance against UV-irradiation may greatly vary among ciliates: for
example, F. salina shows a resistance about tenfold greater than that of B. undulans ,
which belongs to the same order Heterotrichida (Table 2).
Some authors have tried to correlate the UV-resistance with the presence of
pigments in the cell cytoplasm; in a white mutant of Blepharisma incertus , for example,