FIG 5.

Transferrin, ferritin, and hemoglobin stimulate C. burnetii replication. To assess whether C. burnetii can utilize iron from host-associated iron-containing proteins, bacterial yields were determined via enumeration of GE after 8 days in ACCM-2^−FeSO4 supplemented with different concentrations of transferrin, ferritin, or hemoglobin (a). Each bar represents the average from 3 independent experiments; error bars indicate SEM. To determine whether the moderately acidic pH of the CCV aids iron release from iron-binding proteins, iron content was measured for 0.5 mg ml⁻¹ of transferrin (b), ferritin (c), or hemoglobin (d) exposed to pH 7.3 or 4.75 for 2 h. Each bar represents the average from 3 independent experiments; error bars indicate SEM. n.s., not significant; *, P < 0.05; **, P < 0.01 (unpaired Student’s t test).