Surface charge density and light-scattering of the Plectonema boryanum spheroplasts

The electrokinetic properties of spheroplasts from the cyanobacterium Plectonema boryanum were examined by particle microelectrophoresis technique. The electrophoretic mobility (EPM) of the particles was determined after incubation with CaCl₂ in dependence of iron content in culture media as follows: an iron sufficient medium (`control' variant), an iron-deficient medium (`Fe-starved' variant) and an excess of iron supply medium (`20×Fe' variant). Strong increase in EPM was observed with micromolar concentrations of divalent cations at `20×Fe' spheroplasts. This pattern of calcium efficiency was not accompanied with the cation influences on the aggregate ability of particles. The EPM of `control' spheroplasts strongly decreased with addition of calcium cations. The `Fe-starved' speroplasts were characterized with a slight reduction in EPM and a mild change in light-scattering properties of the particles. The data is the direct demonstration of the interaction between calcium cations and spheroplast surface, which could be proposed to play a role in the environmental cycling of iron.