Autophagy and heavy metal induced stress in green algae. Invited lecture L5

Various genera and species of unicellular green algae proved to be resistant, at different level of effectiveness to heavy metals pollution (Kumar et al. 2015). For instance, species of genera Chlorella (Kumar et al. 2015), Dichtiosphaerium (Pereira et al. 2015) and Micrasterias (Lütz- Meindl 2016) showed different level of resistence depending on the strain and populations. The presence of heavy metals in water can be faced by these organisms in very different ways, with respect to the metal involved and to the strategy carried out by the cell itself. Some cells may arrest the metals at the wall level, by excluding the entrance into the cytoplasm, other may concentrate and precipitate the metal in a vacuole. Besides these methods, some cells appear to increase their turn over by increasing autophagic activity in order to replace organels that get damaged by the heavy metal toxicity. Some preliminary results in Dictiosphaerium may even suggest that some members of the populations accumulate faster the heavy metals than the others, eventually dieing subtracting part of the metal from the medium. If confirmed, this activity would represent a Programmed Cell Death case resembling the sacrifice of some cells in multicellular organisms in order to accomplish a specific task of general interest for the entire organisms. Such cases are quite rare or of difficult interpretation in unicellular organisms. The strategy with which such unicellular (or colonial) genera of green algae are able to resist to heavy metals in the environments is object of interest (see, for instance), since the method to reduce the biological effects may provide strains capable of production of industrial products even in polluted cultures and/or suggest methods to remove the heavy metals from polluted