The regulatory pathway that coordinates expression of the <italic>Legionella pneumophila</italic> transmission phenotype with entry into stationary phase.
Hammer, Brian Keith
2001
Abstract
Pathogenic <italic>Legionella pneumophila</italic> evolved as a parasite of aquatic amoebae. To persist in the environment, the microbe must be proficient at both replication and transmission. Previous studies of <italic>L. pneumophila </italic> showed that several traits correlated with virulence were expressed only in the post-exponential (PE) phase. Specifically, unlike replicating bacteria, PE phase <italic>L. pneumophila</italic> were motile, sodium sensitive, cytotoxic, and proficient for infecting macrophages and evading phagosome-lysosome fusion. Amino acid limitation appeared to trigger virulence expression because replicating bacteria became virulent after incubation in PE phase broth, but not when it was supplemented with amino acids. The current study began with the hypothesis that accumulation of the amino acid starvation signal guanosine 3<super>'</super>,5<super>'</super>-bispyrophosphate (ppGpp) in <italic> L. pneumophila</italic> coordinates virulence expression with the PE phase. Consistent with this hypothesis, <italic>L. pneumophila</italic> induced to express the <italic>E. coli</italic> RelA ppGpp synthetase accumulated ppGpp, exited exponential phase, and expressed several PE phase virulence traits, including a flagellin gene reporter (<italic>flaAgfp</italic>). To identify components of this regulatory pathway, mutagenized isolates of wild-type <italic> L. pneumophila</italic> carrying <italic>flaAgfp</italic> were screened for decreased flagellin and virulence expression. Five activators of <italic> L. pneumophila</italic> virulence were identified: LetA/LetS, a two-component regulator homologous to <italic>Pseudomonas</italic> GacA/GacS; the stationary phase sigma factor RpoS; the flagellar sigma factor FliA; and a non-coding locus, <italic>letE</italic>. Unlike wild-type bacteria, PE phase <italic> letA</italic> and <italic>letS</italic> mutants did not convert to the virulent form. Moreover, the response by all of the mutants to ppGpp was deficient: when induced to express RelA, the bacteria exited exponential phase, but failed to express virulence traits. In striking contrast, intracellular replication was not affected by <italic>letA, letS, letE,</italic> or <italic>fliA</italic> mutations. A plausible model generated from these results is that as the nutrient supply wanes, intracellular <italic>L. pneumophila</italic> accumulate ppGpp, which activates a signaling pathway mediated by LetA/LetS, RpoS, and FliA to coordinate differentiation from a replicative to a transmission phase. In the transmission phase, <italic>L. pneumophila</italic> expresses a cytotoxin to escape from the spent host, is osmotically resistance to tolerate reintroduction to fresh water, induces motility to translocate to a new host cell, and makes factors that inhibit phagosome-lysosome fusion.Subjects
Coordinates Entry Expression Legionella Pneumophila Pathway Phase Phenotype Ppgpp Regulatory Stationary Transmission Virulence
Types
Thesis
Metadata
Show full item recordCollections
Remediation of Harmful Language
The University of Michigan Library aims to describe library materials in a way that respects the people and communities who create, use, and are represented in our collections. Report harmful or offensive language in catalog records, finding aids, or elsewhere in our collections anonymously through our metadata feedback form. More information at Remediation of Harmful Language.
Accessibility
If you are unable to use this file in its current format, please select the Contact Us link and we can modify it to make it more accessible to you.