Sorption of some ions by algae related to their trophic conditions

The unicellular algae Scenedesmus obliquus (125), Chlorella pyrenoidosa (82) and Coccomyxa solorinae saccatae (111) were studied with respect to the form of uptake of potassium, phosphate, calcium and zinc ions and to the energy sources involved: light under autotrophic conditions, glucose under mixotrophic or heterotrophic conditions (in light and in darkness or together with yeast extract as an auxotrophic substrate). We respected the trophic conditions of algae when preparing the experimental material (precultivation). The following conditions were reached: The three algae grow faster in a glucose medium under mixotrophic conditions and are capable of growing on it also heterotrophically: Ch. pyrenoidosa and Sc. obliquus grow substantially better than C. solorinae saccatae . The first two algae grow more intensively in a glucose medium containing yeast extract while Coccomyxa does not. After cultivation under mixotrophic conditions the first two diminish endogenous respiration, the third raises it. Glucose stimulates respiration in the first two when grown autotrophically, while after mixotrophic cultivation the effect of glucose is suppressed in Ch. pyrenoidosa and in the other two only after growth on glucose with yeast extract. A relationship between sorption and metabolism was established for potassium in all the algae investigated. The effect of light is generally positive, heterotrophic components (glucose and possibly yeast extract) stimulate the uptake in the dark as long as they represent a suitable mixotrophic medium for the given alga. The uptake of K + was proportional to concentration in solution and independent of Ca 2+ . The uptake of phosphate is clearly stimulated by light, while no stimulation under mixotrophix or heterotrophic conditions on glucose was observed—actually, a depression usually took place. At concentrations from 10 −6 M to 10 −2 M the uptake of phosphate is non-linearly but positively related to the concentration in the medium. The presence of Ca 2+ is the cause of non—metabolic forms of phosphate sorption. Two forms of calcium uptake were found: the predominant one is adsorption which can be associated with the presence of phosphate ions; the metabolic uptake represents a considerably lower fraction which is characterized either by a light dependence or at least by a rise of calcium content between t=0.1–6 h. The absorbed Ca 2+ can be washed out up to 75% with dilute hydrochloric acid. The total adsorption and remainder after washing depend on the pH of the solution from which the sorption took place (a considerable rise beyond pH 6·5). A substantial effect on the formation of the adsorption system was found to be due to organic nutrients. Algae after mixotrophic precultivation possess a decreased sorptive capacity.