Growth and Cytology of Chlamydomonas acidophila Under Acidic Stress

Acid deposition has attracted considerable attention in both the scientific literature and the popular press over the last thirty years. Despite reductions in SO sub(2), NO sub(x) and volatile organic carbon emissions following the 1990 Clean Air Act Amendments, there have been no changes in US rain acidity (Howells 1995). Furthermore, many lakes and streams particularly concentrated in the Adirondacks, the mid-Appalachia, the mid-Atlantic Coastal Plain and the High Elevation West remain acidified or are undergoing episodic acidification. Acidification of aquatic environments is accompanied by profound changes in phytoplanktonic communities (Anderson et al. 1997), including reduction of species richness due to the disappearance of sensitive species and the proliferation of tolerant ones (Turner et al. 1991). At the biochemical level, increasing concentrations of hydrogen ions interfere with nutrient uptake and influence the availability, speciation and toxicity of aquatic pollutants (Lustigman et al. 1995). While the effects of hydrogen or hydroxyl ions on algal physiology have been extensively documented (Gimmler et al. 1988; Tatsuzawa et al. 1996), their effects on the fine structure of algal cells have been neglected altogether. Although ultrastructure is an insensitive indicator of stress, when examined in association with more sensitive parameters, it can provide valuable insight on mechanisms of toxicity and tolerance (Visviki and Rachlin 1992; 1994). The present study attempts to remedy this paucity of data, by examining the growth response of Chlamydomonas acidophila Negoro to varying pH, and correlating it with alterations in the cytology of the chlorophyte. This species has been selected because some of its strains have been isolated from acidic bogs and can grow at pH 2.0 (Cassin 1974). Thus, it would be interesting to see whether it has special adaptations for survival in acidic environments.