Affiliation:
1. Department of Microbiology and Immunology, Northwestern University Medical School, Chicago, Illinois 60611
Abstract
ABSTRACT
The mechanisms by which
Legionella pneumophila
, a facultative intracellular parasite and the agent of Legionnaires' disease, acquires iron are largely unexplained. Several earlier studies indicated that
L. pneumophila
does not elaborate siderophores. However, we now present evidence that supernatants from
L. pneumophila
cultures can contain a nonproteinaceous, high-affinity iron chelator. More specifically, when aerobically grown in a low-iron, chemically defined medium (CDM),
L. pneumophila
secretes a substance that is reactive in the chrome azurol S (CAS) assay. Importantly, the siderophore-like activity was only observed when the CDM cultures were inoculated to relatively high density with bacteria that had been grown overnight to log or early stationary phase in CDM or buffered yeast extract. Inocula derived from late-stationary-phase cultures, despite ultimately growing, consistently failed to result in the elaboration of siderophore-like activity. The
Legionella
CAS reactivity was detected in the culture supernatants of the serogroup 1 strains 130b and Philadelphia-1, as well as those from representatives of other serogroups and other
Legionella
species. The CAS-reactive substance was resistant to boiling and protease treatment and was associated with the <1-kDa supernatant fraction. As would also be expected for a siderophore, the addition of 0.5 or 2.0 μM iron to the cultures repressed the expression of the CAS-reactive substance. Interestingly, the supernatants were negative in the Arnow, Csáky, and Rioux assays, indicating that the
Legionella
siderophore was not a classic catecholate or hydroxamate and, hence, might have a novel structure. We have designated the
L. pneumophila
siderophore legiobactin.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
63 articles.
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