Selective Requirement of the Shikimate Pathway of Legionella pneumophila for Intravacuolar Growth within Human Macrophages but Not within Acanthamoeba

Abstract

bLegionella pneumophila utilizes the Dot/Icm type IV translocation system to proliferate within a vacuole in a wide variety of natural amoebal hosts and in alveolar macrophages of the human accidental host. Although L. pneumophila utilizes host amino acids as the main sources of carbon and energy, it is not known whether de novo synthesis of amino acids by intravacuolar L. pneumophila contributes to its nutrition. The aroB and aroE genes encode enzymes for the shikimate pathway that generates the aromatic amino acids Phe, Trp, and Tyr. Here we show the aroB and aroE mutants of L. pneumophila to be defective in growth in human monocyte-derived macrophages (hMDMs) but not in Acanthamoeba spp. The aroB and aroE mutants are severely attenuated in intrapulmonary proliferation in the A/J mouse model of Legionnaires' disease, and the defect is fully complemented by the respective wild-type alleles. The two mutants grow normally in rich media but do not grow in defined media lacking aromatic amino acids, and the growth defect is rescued by inclusion of the aromatic amino acids, which are essential for production of the pyomelanin pigment. Interestingly, supplementation of infected hMDMs with the three aromatic amino acids or with Trp alone rescues the intramacrophage defect of the aroE but not the aroB mutant. Therefore, the shikimate pathway of L. pneumophila is differentially required for optimal growth within human macrophages, which are auxotrophic for Trp and Phe, but is dispensable for growth within the Acanthamoeba spp. that synthesize the aromatic amino acids.

Multiple Substrate Usage of Coxiella burnetii to Feed a Bipartite Metabolic Network

“…On one hand, in vitro grown L. pneumophila does not need to use this pathway for the de novo biosynthesis of aromatic amino acids and rather imports these amino acids from the medium. On the other hand, recent studies demonstrated that mutants of L. pneumophila concerning two enzymes of the shikimate pathway, aroB and aroE , were defective in infection and replication inside of human macrophages (Jones et al, 2015 ).…”

The life stage‐specific pathometabolism of Legionella pneumophila

“…Carbon from glucose was detected in amino acids and in PHB, and only a minor enrichment was found in mannose . The importance of available amino acids for the replication of L. pneumophila within the LCV was also shown in further experiments using different mutant strains . The data indicate that different substrates can be metabolized independently during the replicative phase .…”

“…In addition, PhtJ was identified as a Val transporter also essential for differentiation and intracellular multiplication of L. pneumophila in macrophages . Recently, it was demonstrated that aroA and aroB , involved in the biosynthesis of aromatic amino acids, are also essential during intracellular replication of L. pneumophila in macrophages . Furthermore, transcriptomic studies demonstrated the upregulation of genes encoding transporters for amino acids and oligopeptides as well as enzymes involved in the metabolism of Glu, Gln, Thr, Lys, Arg and His during intracellular replication .…”

“…This process is also called ‘nutritional evolution’ . For example, the shikimate pathway of L. pneumophila is required for optimal growth within human macrophages, which are auxotrophic for Trp and Phe, but this pathway is dispensable for growth within Acanthamoeba due to the fact that Acanthamoeba is able to synthesize aromatic amino acids .…”

Pathogenicity and Virulence ofLegionella: Intracellular replication and host response

“…Moreover, LamA augments IFN-γ-mediated IDO1 activity, which depletes cellular tryptophan. Although L. pneumophila is not auxotrophic for tryptophan, host-derived tryptophan is important for L. pneumophila replication within macrophages [ 192 , 193 ].…”