Influence of Deleterious Concentrations of Copper on the Growth of <i>Chlorella pyrenoidosa</i>

Abstract

Abstract The effect of deleterious concentrations of ionic Cu on the growth of Chlorella pyrenoidosa has been studied. An earlier paper showed a distinct effect of the same concentrations on the photosynthesis of the alga. Several substances, e.g. Fe and citric acid counteract the effect of Cu. In media ordinarily used for growing unicellular algae the influence of Cu is relatively slight due to the extraordinarily large concentrations. of Fe. At a concentration of 6 μg/I Fe – near to that in nature –even one μg/I Cu significantly decreases the growth during the first 24 hours. Cu is adsorbed to the negative charges on micelles of Fe(OH) 3 created in the alkaline medium. Citric acid is readily assimilated by Chlorella and thus counteracts the influence of Cu for only relatively short period. Cell concentration is of decisive importance for the deleterious influence of Cu on growth. The effect of a certain Cu concentration stops at a certain concentration of of the algae regardless of whether the experiment is started at this cell concentration or this concentration is attained during the experiment. This is due to the binding of Cu by the organic matter of cell walls and slime envelopes. H + ions compete with Cu both when combining with the organic matter in the cell walls and when occupying the active sites of the cell membranes. The latter explains the fact that the influence of Cu is only slight at pH 5 compared with that at pH 8. At a Cu‐concentration where no growth of algae can take place, the algae are by no means killed. After being transferred to an ordinary medium the algae start to grow again. The influence of Cu depends on the division stage of the algae. If the initial steps of cell division have taken place, the cell continues to divide.