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

Changes induced on freshwater microalga Dictyosphaerium chlorelloides (Dc(wt)) 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 (Dc(CdR100)) 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 Dc(CdR100) strain exhibited significant cell morphology changes in comparison to Dc(wt) cells, which affected both surface area and cell biovolume. Malthusian fitness analysis showed that Dc(CdR100) 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. Dc(CdR100) 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 Dc(CdR100) cells suggest the possibility of using this strain in conjunction with Dc(wt) strain as bioelements into a dual-head biosensor, and in bioremediation processes on freshwater polluted with Cd.

Physical properties and composition of femurs of rat fed with diets based on corn tortillas made from different processes.

In this study the effect of calcium absorption on some physical properties and composition of rat femurs was evaluated, comparing rats fed with raw whole corn (RC), tortillas made from extruded masa with 0.25% lime content (TEWL) and without lime (TE), and nixtamal tortillas (NT). The diets were formulated to contain the same amount of protein, oil, fiber, vitamins and minerals other than calcium. In all diets 0.20% calcium was added. At the end of the trials, the femurs were extracted, weighed and measured for ash, calcium and phosphorus content, some physical dimensions, and the crystallinity percentage. The femurs of rats fed with TEWL and NT were heavier, thicker, longer and had higher calcium content. On the other hand, the force required to break the femur of rats fed on ETWL and NT was 1.25 kg greater than that required to break the femurs of rats fed with RC. Higher crystallinity percentage values were observed in the femurs of the rats fed with NT (37.66%) and TEWL (36.98%) as compared to a 30.31% value obtained with the RC.