%0 Journal Article %A Utkilen, Hans Christian %T Magnesium-limited Growth of the Cyanobacterium Anacystis nidulans %D 1982 %J Microbiology, %V 128 %N 8 %P 1849-1862 %@ 1465-2080 %R https://doi.org/10.1099/00221287-128-8-1849 %I Microbiology Society, %X SMg2+-limited growth of the cyanobacterium Anacystis nidulans was investigated in batch and chemostat cultures. In batch cultures the growth rate of the organism depended on the Mg2+ concentration up to 5 μm. Although the maximum growth rate was achieved at this concentration, the organism formed aseptate filaments of three to four times the‘normal’ cell length. About 90 min after increasing the Mg2+ concentration from 5 μm to 1 mm the cell size decreased, followed by an increase in the division rate, which lasted for about 60 min and resulted in a 66% increase in cell number. The rates of DNA, RNA and protein synthesis were not altered during these Mg2+ shift-up experiments, showing that the control by Mg2+ of growth had been separated from its control of cell division, In Mg2+-limited chemostat cultures, the mean cell volume decreased from about 2·0 to 0·6 μm3 when the Mg2+ concentration was increased from 2·5 to 10 μm. This increase in Mg2+ also resulted in an increase in the calculated intracellular Mg2- concentration from 27 to 78 mm, and the amount of cellular Mg2+ bound in chlorophyll increased from 17 to 22%. A comparison of Mg2+-and SO4 2−-limited chemostat cultures showed that the mean cell volume decreased with increasing dilution rate when Mg2+ was the limiting factor, whereas it increased with dilution rate when SO4 2− was limiting. Only small differences in the rates of RNA and protein synthesis were found in the two cultures, although the synthesis of RNA was Mg2+-dependent. The ratio of total RNA to protein, which gives the amount of RNA necessary to synthesize one protein unit (RNA efficiency), was independent of the growth rate in both SO4 2−-and Mg2+-limited chemostat cultures showing that the efficiency of culture RNA was variable in both cases. The efficiency was higher under SO4 2−-than Mg2+-limited conditions. %U https://www.microbiologyresearch.org/content/journal/micro/10.1099/00221287-128-8-1849