ThinkIR: The University of Louisville\u27s Institutional Repository
Abstract
Legionella pneumophila is an environment organism that parasitizes a wide range of protozoa. Growth within the environmental host primes L. pneumophila for infection of human alveolar macrophages when contaminated aerosols are inhaled. Intracellular replication within either host requires the establishment a replicative niche, known as the Legionella-containing vacuole (LCV). Biogenesis of the LCV depends on the type IVb translocation system, the Dot/Icm, to translocation \u3e320 effectors into the host cytosol. Effectors are responsible for preventing lysosome fusion to the LCV, recruitment of ER-derived vesicles to the LCV, and modulation of a plethora of host processes to promote the intracellular survival and replication of L. pneumophila. Nutrient requirements of the pathogen are reflective of its intracellular lifecycle, consuming host amino acids for carbon and energy. Amino acids, particularly serine and cysteine, are used to generate pyruvate to feed into the TCA cycle, which is the main metabolic pathway for generation of energy. Endogenous levels of host amino acids are insufficient to support robust intracellular replication. Excess host amino acids are generated by the AnkB effector through ubiquitination and proteasomal degradation of host proteins in the cytosol. Host amino acids must be transported across the LCV membrane to be utilized by L. pneumophila. Host solute carrier (SLC) transporters are the most likely candidate to import amino acids into the LCV lumen, as they have been detected in the LCV proteome of multiple mass-spectrometry studies. We sought to confirm the role of human SLCs in nutrient acquisition during intracellular growth of L. pneumophila. No amino acid-transporting SLCs were confirmed to colocalize to the LCV by confocal microscopy. However, a glucose transporter, SLC2a1/Glut1 was shown to be recruited the LCV in a Dot/Icm-dependent manner. The role of glucose in intracellular replication of L. pneumophila is poorly understood. Glucose minimally used through glycolysis, but metabolized through the Enter-Doudoroff pathway. Glucose does not support the replication of L. pneumophila during in vitro growth. We identified 10 SLC-like transporters in L. pneumophila based on their structural similarity to human SLCs. We characterized the role of two putative SLC-like glucose transporters, LstA and LstB of L. pneumophila, in import of glucose and in intracellular replication within human macrophages and amoebae. Single transporter mutants decrease L. pneumophila’s ability to import glucose but do not affect the ability to replicate within the host. Interestingly, the double mutant, lstA/lstB, is severely defective for import of glucose and for intracellular replication within human macrophages and Acanthamoeba polyphaga. These data show that glucose uptake by the redundant transporters, LstA and LstB, is required for in vivo growth. L. pneumophila encodes putative amylases effectors that may be degrading host glycogen as a means to generate glucose that is imported by LstA and LstB. We characterized the L. pneumophila amylase, LamB, because of its uniqueness amongst Legionella species. Here we describe LamB as a functional amylase that is required for intracellular replication of L. pneumophila in human macrophages and A. polyphaga. Additionally, the lamB mutant is completely attenuated in intra-pulmonary proliferation in the A/J mouse model. Taken together, these data further characterize nutritional virulence of L. pneumophila
