Effects of Iron Starvation on the Physiology of the Cyanobacterium Agmenellum quadruplicatum.

The effects of iron starvation on the growth and physiology of the unicellular cyanobacterium Agmenellum quadruplicatum were studied. Uptake of iron from the medium did not occur at a constant rate. The majority of the iron was removed at two different times, when the cells were initially inoculated into the medium and after the cultures had become quite dense and had stopped growing. Iron became limiting for growth 16 h after transfer to an iron-deficient medium, but cultures retained full viability for at least 212 h. Once iron became limiting, c-phycocyanin and chlorophyll a were degraded concurrently. This was followed by an accumulation of intracellular glucose in place of the c-phycocyanin. Nitrate and nitrite reductase activities were elevated through 50 h, after which they decreased steadily. The photosynthetic unit size also increased through 50 h and then decreased. Once iron was restored to the culture medium, growth resumed. The intracellular pigment levels increased rapidly as the glucose level diminished.