FIGURE 4: Influence of cobalt starvation on Anabaena and btuB mutants. (A) Wild-type Anabaena, AFS-I-btuB1 and AFS-I-btuB2 were grown for 5 days in YBG11 medium (+Co, green) or for 14 days in YBG11 medium without cobalt (-Co, magenta) followed by the determination of the intracellular manganese (left), iron (middle) or copper (right) content shown as atoms per cell. (B) The cobalt content of the strains used in A was determined, analyzed and represented as in A. In (A) and (B) the average of three independent experiments is shown; error bars indicate standard deviations. Statistical analysis on three independent replicas was performed as described in methods. The letters indicate the ranks based on statistical analysis performed using ANOVA (p<0.05). (C) Wild-type Anabaena, AFS-I-btuB1 and AFS-I-btuB2 were grown for 14 days in YBG11 medium without cobalt. Cultures were photographed (top) and filaments were visualized by light microscopy using a 40x objective (bottom). Black triangles indicate filament fragments or single cells.