# Using Legionella-amoeba co-evolution to reveal new modes of immunity and pathogenesis

> **NIH NIH R00** · UNIVERSITY OF PITTSBURGH AT PITTSBURGH · 2021 · $316,352

## Abstract

PROJECT SUMMARY
Legionella pneumophila is an opportunistic bacterial pathogen that causes outbreaks of a lethal, pneumonia-
like disease. Although human infections are evolutionary “dead ends” for these bacteria, Legionella
nevertheless carry extensive molecular arsenals to attack human cells due to their adaptation to their natural
hosts, environmental amoebae. Residence in amoebae also protects Legionella from antibiotics and other
efforts to eliminate the bacteria from man-made structures, perpetuating human outbreaks. Revealing how
Legionella exploits host amoebae—particularly steps vulnerable to disruption—therefore has direct benefits for
human health. This proposal will investigate how molecular “arms races” between Legionella and amoebae
have shaped the molecular toolkit of this pathogen, and address the specific hypothesis that Legionella
secreted effector proteins are engaged in arms races with amoeba immune pathways. The experimental
tractability and evolutionary resources available for Legionella and amoebae make this a powerful host-
microbe model system, where it is possible to test the functional consequences of evolutionary innovation in
both host and microbe. Aim 1 will investigate how Legionella has been impacted by such an arms race.
Evolutionary approaches will analyze this organism's enormous arsenal of molecular weaponry, the type IV
effectors, to identify genes and residues likely engaged in arms races with hosts. Bacterial genetics will then be
used to functionally test evolutionary hypotheses about which genes or residues are critical for pathogen
fitness. These studies will begin with the mavN gene, which appears to be engaged in an evolutionary “battle
for iron” within host cells. In addition to such competitions for resources, many pathogens have evolved
strategies to evade detection by host immune systems. High-throughput transposon-sequencing approaches
will be used to identify bacterial genes that are required for fitness within Dictyostelium amoebae, particularly
those that interact with amoeba immunity. These experiments will reveal which Legionella proteins have
experienced strong selective pressures in amoeba hosts. Aim 2 will examine the host genes likely to place
strong selective pressures on Legionella through studies of amoeba immune defenses. The Dictyostelium TirA
protein is related to Toll-like receptors in animals, and helps the amoebae to resist Legionella infection.
However, beyond these basic facts, almost nothing is known about amoeba immunity. This aim will further
characterize the activity of the TirA immune pathway, identifying additional members of the immune pathway
and transcriptional targets. Evolutionary and unbiased genetic approaches will highlight additional arms of the
amoeba immune response that respond to Legionella infection. The proposal will combine the applicant's
background in evolution, genetics, and host-microbe interactions with the Malik lab's expertise in evolutionary
arms rac...

## Key facts

- **NIH application ID:** 10200673
- **Project number:** 5R00AI139344-04
- **Recipient organization:** UNIVERSITY OF PITTSBURGH AT PITTSBURGH
- **Principal Investigator:** Tera Catherine Levin
- **Activity code:** R00 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $316,352
- **Award type:** 5
- **Project period:** 2020-07-01 → 2023-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10200673

## Citation

> US National Institutes of Health, RePORTER application 10200673, Using Legionella-amoeba co-evolution to reveal new modes of immunity and pathogenesis (5R00AI139344-04). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10200673. Licensed CC0.

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