Growth of H. influenzae strains with protoporphyrin IX. Growth of the H. influenzae strain Rd KW20 and the dppC insertion mutant strain TMV1262 in hdBHI supplemented with protoporphyrin IX at either 2.5 or 0.5 μg ml-1 and additionally supplemented with 200 μM ferrous ammonium sulfate. Wildtype strain Rd KW20 with protoporphyrin IX at 2.5 μg ml-1 (solid circles) and at 0.5 μg ml-1 (open circles). The dppC insertion mutant strain TMV1262 with protoporphyrin IX at 2.5 μg ml-1 (closed triangles) and at 0.5 μg ml-1 hemoglobin equivalent (open triangles). Results are mean ± SD for quintuplicate results from representative experiments. The Kruskal-Wallis test was used to compare growth of Rd KW20 and TMV1262 over the entire 48 hour growth period at either concentration of protoporphyrin IX (P < 0.0001 for both comparisons). Optical density measurements were taken every 30 minutes, however, for the purpose of the clarity of data presentation only hourly time points have been plotted.