FIG. 5.

Ferric reductase activity in culture supernatants of different strains of L. pneumophila. Strains 130b (black bar), JR32 (white bar), Los Angeles 1 (gray bar), and Dallas 1 (hatched bar) were grown in CDMP for 24 h and then filter-sterilized culture supernatants were tested for their ability to reduce ferric nitrate as described above. The horizontal line depicts the level of background activity exhibited by the medium control. The data are the means and standard deviations from triplicate cultures.