Effects of heavy-metal stress on cyanobacterium Anabaena flos-aquae

The influence of two metals, copper and cadmium, was studied on the growth and ultrastructures of cyanobacterium Anabaena flos-aquae grown at three different temperatures: 10 degrees C, 20 degrees C, and 30 degrees C. The highest concentration of chlorophyll a was observed at 20 degrees C and the lowest at 10 degrees C. Both toxic metal ions, Cu(2+) and Cd(2+), inhibited growth of the tested cyanobacterium. Chlorophyll a concentration decreased with the increase of metal concentration. A 50% decrease in the growth of A. flos-aquae population, compared with the control, was reached at 0.61 mg l(-1) cadmium and at 0.35 mg l(-1) copper (at 20 degrees C). Copper at all temperatures tested was proven to be more toxic than cadmium. At 3 mg l(-1), the lysis and distortion of cells was observed; however, after incubation at 9 mg l(-1) cadmium, most of the cells were still intact, and only intrathylakoidal spaces started to appear. Copper caused considerably greater changes in the protein system of A. flos-aquae than did cadmium; in this case, not only phycobilins but also total proteins were destructed. The aim of this study was also to identify the place of metal accumulation and sorption in the tested cyanobacterium. Analysis of the energy-dispersion spectra of the characteristic x-ray radiation of trichomes and their sheaths showed that cadmium was completely accumulated in cells but was not found in the sheath. Spectrum of the isolated sheath after treatment with copper exhibited only traces of the metal, but isolated cells without a sheath showed a high peak of copper.