The aim of this study was to determine structural changes induced by the free copper ion in fully hydrated cells of the flagellate protozoon Chilomonas paramecium, a common inhabitant of polluted waters, and often exposed to fluctuating levels of external metals. Light microscopy showed that C. paramecium was sensitive to copper; the cells rounded up within minutes of exposure to 2.5 mg/l copper, and were almost spherical within 20 minutes. However, they were able to tolerate the increased copper level, and remained in this altered state for weeks. Soft X-ray microscopy showed that compartments formed and ejectosomes were released in response to initial copper exposure. All cells exposed for 28 hours had a posteriorly positioned indentation that could not be correlated to the vestibulum. Some cells had regenerated their flagella. Quantified data pertaining to changes in the pellicle width after copper exposure of live, fully hydrated cells with natural specimen contrast are given.
