This study investigates whether manganese (Mn²⁺) can functionally replace magnesium (Mg²⁺) during cell division in the cyanobacterium Anacystis nidulans. Using chemostat cultures limited by low Mg²⁺ concentration (6 μM), researchers progressively increased medium Mn²⁺ levels and monitored cellular responses. When reservoir Mn²⁺ increased from 9.5 to 15 μM, mean cell volume decreased dramatically from 1.3 to 0.4 μm³, indicating restored cell division despite Mg²⁺ limitation. The cellular Mn²⁺ concentration increased approximately fourfold while intracellular Mg²⁺ remained constant at ~100 mM. Higher Mn²⁺ concentrations (20-100 μM) inhibited overall biomass production by reducing Mg²⁺ uptake, though cells remained small. Batch culture experiments showed Mn²⁺ additions partially restored cell division, causing cell volume to decline about 60 minutes post-shift-up, but without the synchronized division observed with Mg²⁺ shifts. The results demonstrate that Mn²⁺ can functionally substitute for Mg²⁺ in the cell division process of A. nidulans, though less effectively than native Mg²⁺.

Key findings

• Increasing medium Mn²⁺ concentration from 9.5 to 15 μM reduced mean cell volume from 1.3 to 0.4 μm³ in Mg²⁺-limited A. nidulans cultures
• Cellular Mn²⁺ concentration increased fourfold while intracellular Mg²⁺ remained constant, indicating Mn²⁺ can partially substitute for Mg²⁺ in cell division
• Higher Mn²⁺ concentrations (≥20 μM) inhibited biomass production by interfering with Mg²⁺ uptake
• Mn²⁺ shift-ups induced cell volume decline but without synchronized cell division, unlike Mg²⁺ shift-ups