EFFECT OF UV-B RADIATION ON CILIATED PROTOZOA - Environmental UV Radiation: Impact on Ecosystems and Human Health and Predictive Models - page 222

EFFECT OF UV-B RADIATION ON CILIATED PROTOZOA
ROBERTO MARANGONI, FABIO MARRONI, FRANCESCO
GHETTI, DOMENICO GIOFFRÉ AND GIULIANO COLOMBETTI
CNR Istituto di Biofisica, Pisa, Italy
1. Abstract
This paper reviews some of the results described in the literature on the effect of
UV-B radiation on ciliated protozoa, concentrating in particular on the changes induced
in motility and photomotility, which are both important in determining the capability of
these organisms to survive in their environment. It will be shortly described what
ciliates are and why they are an important component of ecological systems. A
summary will follow of the early works, where the effects of UV radiation on ciliates
were investigated. Finally, it will be described in some more detail the results of studies
on a marine ciliate, Fabrea salina , and two fresh-water ciliates, Blepharisma japonicum
and Ophryoglena flava .
2. Introduction
The amount of UV-B radiation that reaches the Earth surface is determined in
first approximation by the ozone concentration in the stratospheric layer. It is widely
acknowledged that the ozone layer has been depleted because of the production of
chemicals such as CFCs and methyl bromide which react with ozone molecules turning
them into oxygen. A consequence of this depletion of the stratospheric ozone layer
might be an increase of the UV-B radiation reaching the Earth.
UVB radiation penetrates to a certain depth in the water (depending on the
turbidity of the water itself), so it can affect phyto- and zooplankton microorganisms in
both marine and fresh-water ecosystems. Recent studies have shown that UV-B
radiation can damage microorganisms in many ways: it can affect growth and metabolic
processes such as photosynthesis. In addition to this, UV-B radiation may impair
motility and the orientation with respect to various stimuli, such as light, gravity and
chemical substances 1 . Microorganisms exposed to UV-B radiation may become unable
to orient themselves in the water column and to find suitable condition for growth and
survival. The biological effects of a possible increase in UV irradiance on our planet,
due to the reduction of the ozone layer, have been investigated in the last twenty years
or so. Among the systems that have been examined, a good deal of work has been done
on single cell systems, where the complex interactions between cells and organs typical
of higher organisms are not present. This makes, in principle, easier to understand the
basic biological processes affected by UV radiation.