A STUDY OF IRON ACQUISITION MECHANISMS OF LEGIONELLA-PNEUMOPHILA GROWN IN CHEMOSTAT CULTURE

We recently demonstrated that the virulence of a clinical isolate of L egionella pneumophila is significantly attenuated when cultured in an iron-limited environment. In this study the influence of iron limitati on on the expression of enzyme activities and iron-transport mechanism s was investigated. Expression of the important pathogenicity factor, the zinc metalloprotease, was reduced fivefold in response to iron lim itation. Ferric citrate reductase activity was demonstrated in both ir on-limited and replete cell fractions. Activity was located principall y in the cytoplasm and periplasm, and was not enhanced by iron restric tion. Optimum activity was observed with NADPH as reductant. Sideropho res were not elaborated under these culture conditions. Iron-loaded tr ansferrin enhanced the growth of steady-state, iron-limited cultures, demonstrating that transferrin represents a potentially important iron source for L. pneumophila in vivo. Although cell surface transferrin receptors were not detected, in vitro experiments demonstrated digesti on of transferrin by the zinc metalloprotease activity of culture supe rnatants.