Ultrastructural changes of Chaetomorpha brachygona growing in metal environment.

Abstract

The structural changes of the filamentous green alga C. brachygona growing in iron-ore tailing which contained high levels of manganese, cadmium, chromium, copper, iron, lead and zinc were investigated with the electron microscope. The most conspicuous ultrastructural change of the algal cells was the substantial increase in the thickness of the side wall and the cross wall between adjacent cells, which could trapped large amounts of metal precipitates. The well lamellated outer portions of the thickened side wall probably functioned in preventing rapid movement of the metal precipitates through the wall into the cell lumen. There was an increase in the number as well as the size of the lipid bodies in the metal-tolerant algal cells. Reduction of the size of the chloroplasts which showed a reduced internal organization was also observed. In addition, the presence of multivesiculate bodies in the cytoplasm which were not detected in normal algal cells, served as reservoir for the sequenstration of metal ions in the cytoplasm. Deposition of metal precipitates was not detected in the chloroplast, mitochondria and nucleus of the cell however. The metal tolerance exhibited by C. brachygona was therefore attributed to these ultrastructural changes of the algal cells, which enabled the algal filaments to survive and maintain growth in the metal-riched environment.