It is increasingly evident that interspecies antagonism is intrinsic to life in the bacterial kingdom. And yet, while our understanding of the antibacterial mechanisms bacteria employ in conflicts with their brethren has recently grown exponentially, our knowledge of the means by which bacteria sense and respond to antagonistic threats remains limited. In this proposal, we test the hypothesis that bacteria react to the presence of an antagonistic bacterial competitor through the activation of a multifaceted defensive program. This hypothesis grew from our discovery that Pseudomonas aeruginosa activates an extensive posttranscriptional regulatory program in response to interbacterial antagonism. The pathway, which we term PARA (Pseudomonas aeruginosa response to antagonism), is triggered when a subpopulation of P. aeruginosa cells succumb to lysis as a result of an antagonistic attack. Detection of as yet unidentified molecule(s) in cellular lysate leads to the activation of the small RNA-mediated Gac/Rsm global posttranscriptional regulatory program. Activation of this response is crucial for P. aeruginosa survival during attack, as a mutant unable to mount the response suffers a severe fitness defect during competition with antagonistic organisms. Finally, we demonstrate that the defensive response requires multiple, simultaneously acting mechanisms, including pathways of unknown function.
In Aim 1 of this proposal, we will characterize one such pathway, which we name ARC1 (antagonism response complex 1). Our preliminary data indicate that ARC1 is a large membrane- associated protein complex that provides P. aeruginosa protection against antagonism mediated by toxins delivered by the type VI secretion system of a competitor species. Our studies of ARC1 will elucidate the range of threats towards which it provides protection and provide mechanistic insight into its defensive functions.
In Aim 2, we will pursue complementary genetic and biochemical approaches directed at characterizing the signal present in P. aeruginosa cellular lysate responsible for triggering PARA. Finally, in Aim 3, we move beyond P. aeruginosa and ask to what extent the regulatory components behind PARA ? the Gac/Rsm pathway ? function generally to defend against interbacterial antagonism in other Pseudomonas species. We also examine the hypothesis that variability in the Gac/Rsm regulon reflects adaptation to the specific bacterial threats encountered by different species. Through this work, we stand to answer longstanding questions in the field, including defining the evolutionarily relevant function of an important global regulatory program and providing a molecular characterization of a long elusive signaling molecule. Additionally, through the characterization of ARC1, our work will define the mechanistic basis for participation of a conserved membrane complex of unknown function in interbacterial defense. Overall, the proposed work stands to broaden our understanding of the ways in which interbacterial antagonism shapes the course of bacterial evolution.

Public Health Relevance

The goal of this study is to gain insight into the mechanisms bacteria employ to defend themselves against antagonistic bacterial competitors. A greater understanding of these bacterial defenses will be beneficial for efforts to combat chronic, multispecies infections and in manipulation of human-associated microbial communities to promote health.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Research Project (R01)
Project #
Application #
Study Section
Prokaryotic Cell and Molecular Biology Study Section (PCMB)
Program Officer
Lu, Kristina
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
University of Washington
Schools of Medicine
United States
Zip Code
LaCourse, Kaitlyn D; Peterson, S Brook; Kulasekara, Hemantha D et al. (2018) Conditional toxicity and synergy drive diversity among antibacterial effectors. Nat Microbiol 3:440-446
Ting, See-Yeun; Bosch, Dustin E; Mangiameli, Sarah M et al. (2018) Bifunctional Immunity Proteins Protect Bacteria against FtsZ-Targeting ADP-Ribosylating Toxins. Cell 175:1380-1392.e14
Verster, Adrian J; Ross, Benjamin D; Radey, Matthew C et al. (2017) The Landscape of Type VI Secretion across Human Gut Microbiomes Reveals Its Role in Community Composition. Cell Host Microbe 22:411-419.e4
Whitney, John C; Peterson, S Brook; Kim, Jungyun et al. (2017) A broadly distributed toxin family mediates contact-dependent antagonism between gram-positive bacteria. Elife 6:
Eshraghi, Aria; Kim, Jungyun; Walls, Alexandra C et al. (2016) Secreted Effectors Encoded within and outside of the Francisella Pathogenicity Island Promote Intramacrophage Growth. Cell Host Microbe 20:573-583
Wexler, Aaron G; Bao, Yiqiao; Whitney, John C et al. (2016) Human symbionts inject and neutralize antibacterial toxins to persist in the gut. Proc Natl Acad Sci U S A 113:3639-44
Whitney, John C; Quentin, Dennis; Sawai, Shin et al. (2015) An interbacterial NAD(P)(+) glycohydrolase toxin requires elongation factor Tu for delivery to target cells. Cell 163:607-19
Chou, Seemay; Daugherty, Matthew D; Peterson, S Brook et al. (2015) Transferred interbacterial antagonism genes augment eukaryotic innate immune function. Nature 518:98-101
LeRoux, Michele; Kirkpatrick, Robin L; Montauti, Elena I et al. (2015) Kin cell lysis is a danger signal that activates antibacterial pathways of Pseudomonas aeruginosa. Elife 4:
LeRoux, Michele; Peterson, S Brook; Mougous, Joseph D (2015) Bacterial danger sensing. J Mol Biol 427:3744-53

Showing the most recent 10 out of 28 publications