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A Legionella pneumophila gene that promotes hemin binding.

ABSTRACT: The ability to bind and utilize hemin is a trait common to many human pathogens. Nevertheless, the relationship between Legionella pneumophila, the agent of Legionnaires' disease, and hemin has received little attention. Thus, we explored the capacity of a virulent, serogroup 1 strain of L. pneumophila to bind hemin and use it as an iron source. Hemin, but not protoporphyrin IX, restored bacterial growth in iron-limiting media, indicating that it can serve as an iron source for L. pneumophila. In support of this idea, we observed that wildtype legionellae were able to bind 50 to 60% of added hemin, a binding capacity that was comparable to those of other pathogens. To begin to identify proteins involved in hemin acquisition, we identified a Legionella locus that conferred hemin binding upon Escherichia coli. Subcloning and nucleotide sequence analysis determined that a single open reading frame, which was designated hbp for hemin-binding promotion, was responsible for this binding activity. The hbp gene was predicted to encode a secreted, 15.5-kDa protein. To ascertain the importance of this gene in L. pneumophila biology, we used allelic exchange to construct an hbp mutant. Importantly, the mutant displayed a 42% reduction in hemin binding, confirming that hbp potentiates hemin acquisition by L. pneumophila. However, the strain was unaltered in its ability to grow within macrophage-like cells and freshwater amoebae, indicating that hbp is not required for intracellular infection. Despite this, Southern hybridization analysis and database searches demonstrated that hbp is nearly exclusive to the L. pneumophila species.

SUBMITTER: O'Connell WA

PROVIDER: S-EPMC173846 | biostudies-other | 1996 Mar

REPOSITORIES: biostudies-other

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A Legionella pneumophila gene that promotes hemin binding.

O'Connell W A WA Hickey E K EK Cianciotto N P NP

Infection and immunity 19960301 3

The ability to bind and utilize hemin is a trait common to many human pathogens. Nevertheless, the relationship between Legionella pneumophila, the agent of Legionnaires' disease, and hemin has received little attention. Thus, we explored the capacity of a virulent, serogroup 1 strain of L. pneumophila to bind hemin and use it as an iron source. Hemin, but not protoporphyrin IX, restored bacterial growth in iron-limiting media, indicating that it can serve as an iron source for L. pneumophila. I ...[more]

PMID: 8641790

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Project description:UnlabelledLegionella pneumophila is a natural parasite of environmental amoebae and the causative agent of a severe pneumonia termed Legionnaires' disease. The facultative intracellular pathogen employs a bipartite metabolism, where the amino acid serine serves as the major energy supply, while glycerol and glucose are mainly utilized for anabolic processes. The L. pneumophila genome harbors the cluster lpg1653 to lpg1649 putatively involved in the metabolism of the abundant carbohydrate myo-inositol (here termed inositol). To assess inositol metabolism by L. pneumophila, we constructed defined mutant strains lacking lpg1653 or lpg1652, which are predicted to encode the inositol transporter IolT or the inositol-2-dehydrogenase IolG, respectively. The mutant strains were not impaired for growth in complex or defined minimal media, and inositol did not promote extracellular growth. However, upon coinfection of Acanthamoeba castellanii, the mutants were outcompeted by the parental strain, indicating that the intracellular inositol metabolism confers a fitness advantage to the pathogen. Indeed, inositol added to L. pneumophila-infected amoebae or macrophages promoted intracellular growth of the parental strain, but not of the ΔiolT or ΔiolG mutant, and growth stimulation by inositol was restored by complementation of the mutant strains. The expression of the Piol promoter and bacterial uptake of inositol required the alternative sigma factor RpoS, a key virulence regulator of L. pneumophila Finally, the parental strain and ΔiolG mutant bacteria but not the ΔiolT mutant strain accumulated [U-(14)C6]inositol, indicating that IolT indeed functions as an inositol transporter. Taken together, intracellular L. pneumophila metabolizes inositol through the iol gene products, thus promoting the growth and virulence of the pathogen.ImportanceThe environmental bacterium Legionella pneumophila is the causative agent of a severe pneumonia termed Legionnaires' disease. The opportunistic pathogen replicates in protozoan and mammalian phagocytes in a unique vacuole. Amino acids are thought to represent the prime source of carbon and energy for L. pneumophila However, genome, transcriptome, and proteome studies indicate that the pathogen not only utilizes amino acids as carbon sources but possesses broader metabolic capacities. In this study, we analyzed the metabolism of inositol by extra- and intracellularly growing L. pneumophila By using genetic, biochemical, and cell biological approaches, we found that L. pneumophila accumulates and metabolizes inositol through the iol gene products, thus promoting the intracellular growth, virulence, and fitness of the pathogen. Our study significantly contributes to an understanding of the intracellular niche of a human pathogen.

Dataset Information

A Legionella pneumophila gene that promotes hemin binding.

Publications

A Legionella pneumophila gene that promotes hemin binding.

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