Physiological studies on heavy metals and blue-green algae

Abstract

Mutants of Anacystis nidulans tolerant to high levels of Co, Ni,Cu, Zn and Cd were obtained by repeated subculturing at strongly inhibitory levels of metal. For instance, the level of Zn at which-1strong inhibition occurred was raised from 1.45 to 16.5 mg 1(^-1) Zn after 75 subcultures. Isolates resistant to 5.0 mg 1(^-1) Zn and 12.0 mg 1(^-1) Zn maintained their resistance for at least 72 cell generations in the absence of Zn, though there was subsequently an increased lag during the first subculture back to high Zn levels. This and plating experiment sindicate that the strains are mutants. Assays of cross-resistance of each of the five types of mutant were made to the other four metals. Inmost cases changes in cross-resistance were only slight, with about equal numbers of examples of increased and decreased resistance. Examples of marked changes were increased Co-resistance of a Cd-tolerant strain and decreased Cd-resistance of a Ni-tolerant strain. The environmental factors influencing toxicity were investigated for Cu, Zn and Cd. Increases in Ca, Mn, Fe and P reduced Zn toxicity to both wild-type and Zn-tolerant strains, but the two differed in their response to pH. Effects on morphology were evident at high metal levels with all strains. In most cases increased levels of metal led to the formation of filaments, but with Cu subspherical structures sometimes made up most of the-1population. Uptake from media enriched 0.1 and 1.0 mg 1(^-1) Zn was similar in both wild-type and Zn-tl2.0, whether judged by total Zn accumulated or by that remaining after EDTA washes. Isolates from high Zn sites were found in general to tolerate considerably higher levels of Zn than laboratory research strains(presumably isolated from environments not enriched with Zn). A comparison of the influence of Zn on nitrogen fixation by a strain from low zinc site{Anabaena cylindrica) and one from a high Zn site (Calothrix D184) showed only a slight difference when Zn was first added, but a pronounced effect after 24 h. [brace not closed]