Morphological and physiological changes exhibited by a Cd-resistant Dictyosphaerium chlorelloides strain and its cadmium removal capacity

Abstract

ABSTRACTChanges induced on freshwater microalga Dictyosphaerium chlorelloides (Dcwt) acclimated in the laboratory until their survival in culture media enriched with cadmium 100 µM have been studied. Cadmium removal by living cells of this Cd-resistant (DcCdR100) strain was tested in cultures exposed to 100 µM Cd during 30 days. Cell dimensions were measured under light microscopy, and cell growth was studied. Photosynthetic yield (ΦPSII) was analyzed and the photosynthetic oxygen development and respiration response was obtained. Results show that DcCdR100 strain exhibited significant cell morphology changes in comparison to Dcwt cells, which affected both surface area and cell biovolume. Malthusian fitness analysis showed that DcCdR100 strain living in Cd-enriched culture had developed a lower capacity of nearly 50% growth, and its photosynthetic oxygen development and respiration response were significantly reduced in both light and dark photosynthetic phases. DcCdR100 strain showed a very high capacity to remove cadmium from the aquatic environment (over 90%), although most of the removed heavy metal (≈70%) is adhered to the cell wall. These specific characteristics of DcCdR100 cells suggest the possibility of using this strain in conjunction with Dcwt strain as bioelements into a dual-head biosensor, and in bioremediation processes on freshwater polluted with Cd.