Physiological and structural responses of the cyanobacterium Anabaena cylindrica to aluminium

When adding aluminium (3.7–370 μM) as AlCl3–6H20 to cultures of the nitrogen‐fixing cyanobacterium Anabaena cylindrica, strain 1403/2a (CCAP), the following responses were observed: The effects of aluminium were dependent on pH. being most drastic at pH 6.0. At this pH the growth of A. cylindrica was significantly reduced by 3.7 μM aluminium and completely inhibited by 370 μM. The content of chlorophyll a and phycocyanin decreased after treatment with aluminium. Also, aluminium lowered the rates of both CO2‐fixation and N2‐fixation with total inhibition of both processes by 370 μM. At the lower concentrations used the nitrogenase activity started to recover after about 100 h. The aluminium content in the cells increased with increasing concentration and with time. At 190 μM the aluminium concentration in the cells represented 2.4 and 3.3% of the dry weight after 6 and 24 h, respectively. Clogging of filaments and lysis of vegetative cells were apparent at higher aluminium concentrations while the frequency of heterocysts increased in all concentrations used. The most pronounced ultrastructural changes included accumulation of cyanophycin granules and degradation of the thylakoids. The ultrastructure of the heterocysts was however not affected. It is concluded that major reasons for the toxicity are interactions with membranes and phosphate deficiency.