Cellular and molecular basis of heavy metal-induced stress in ciliates

Globally, heavy metals are the major pollutants present in both terrestrial and aquatic ecosystems. Increase in their concentration due to various anthropogenic activities is a matter of concern. Higher concentration of these metals is known to be toxic due to their non-biodegradable nature. Eukaryotic microorganisms, ciliates can be used as cellular tools to assess and study the various mechanisms to overcome heavy metal toxicity. Here we discuss, at cellular level, the effect of heavy metal toxicity on growth rate, behavioural and morphological changes of ciliates. At the molecular level, changes in stress genes like hsp70, metallothionein and expression of various antioxidant enzymes (superoxide dismutase, glutathione peroxidase) adopted by ciliates have also been deliberated. It is also being argued that ciliates can be used as biosensor/cellular tools for detecting heavy metal pollution.