The environment of a cell has a profound influence on its physiology, development, and evolution. Caulobacter crescentus, a bacterial model for the study of cell cycle control and development, provides an excellent experimental system to investigate the molecular basis of environmental perception and adaptation. The goal of this proposal is to define the molecular and cellular mechanisms of how light and stress signals are integrated by a bacterium to regulate the cell envelope and cell adhesion. LOV-histidine kinases (LOV-HKs), a newly-discovered class of blue-light photosensors, are conserved across a range of prokaryotes. Although the regulatory roles of LOV- HKs are not well understood, these signaling proteins have recently been shown to control virulence in Brucella abortus and cell adhesion in Caulobacter in response to light. Prior to these discoveries, neither Caulobacter nor Brucella were known or presumed to respond to visible light. Indeed, the majority of species encoding LOV-HKs are chemotrophs with no predicted photobiology. We have uncovered a regulatory network in Caulobacter in which the LOV-HK, LovK, and the receiver protein, LovR, form a form a regulatory feedback loop with CT, an envelope stress sigma factor that is critical for cell survival under osmotic and oxidative stress. The experiments detailed in this proposal will test the hypothesis that LovK/LovR system is part of a novel signaling network in which classical two- component signaling and C-dependent control of transcription intersect to regulate the composition of the cell envelope in response to multiple physical and chemical cues in the environment. We will use a combination of methods to define how interaction between the chemical and light environments affect cellular stress adaptation, cell envelope composition, and cell adhesion. Specifically, we will answer the following questions: (i) How does the LovK/LovR two-component system regulate cell envelope composition and cell adhesion in response to light, (ii) What are the regulatory interactions between the LovK/LovR photosensory network and the CT stress-response network, and (iii) What are the transcriptional targets of CT, CU, and PhyR, three sigma factors that appear to be regulated by CT? Time permitting, we use genetic and biochemical screens to identify additional regulators in the LovK/LovR adhesion pathway. Our experiments will advance our understanding of photoregulation by LOV-HKs, an important new area of prokaryotic biology that impacts bacterial pathogenesis. More generally, these studies will provide important data on mechanisms bacteria use to sense and integrate multiple environmental stimuli in a fluctuating environment, which is critical for bacterial cell survival.

Public Health Relevance

Histidine kinases and response regulators, known commonly as two-component signaling proteins, are essential virulence factors in numerous bacterial pathogens including Staphylococcus aureus and Brucella abortus. A newly-discovered class of photosensory histidine kinases, known as the LOV- HKs, regulate virulence in Brucella abortus and cell adhesion in Caulobacter crescentus in response to visible light. Our proposed research on LOV-HK regulation of cell physiology using the powerful Caulobacter model system promises to provide insight into new modes of photoregulation in bacteria, including the molecular and cellular basis of light-mediated virulence in the class III pathogen Brucella.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Prokaryotic Cell and Molecular Biology Study Section (PCMB)
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Anderson, James J
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University of Chicago
Schools of Medicine
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Luebke, Justin L; Eaton, Daniel S; Sachleben, Joseph R et al. (2018) Allosteric control of a bacterial stress response system by an anti-? factor. Mol Microbiol 107:164-179
Tien, Matthew Z; Stein, Benjamin J; Crosson, Sean (2018) Coherent Feedforward Regulation of Gene Expression by Caulobacter ?T and GsrN during Hyperosmotic Stress. J Bacteriol 200:
Tien, Matthew; Fiebig, Aretha; Crosson, Sean (2018) Gene network analysis identifies a central post-transcriptional regulator of cellular stress survival. Elife 7:
Hentchel, Kristy L; Reyes Ruiz, Leila M; Curtis, Patrick D et al. (2018) Genome-scale fitness profile of Caulobacter crescentus grown in natural freshwater. ISME J :
Herrou, Julien; Crosson, Sean; Fiebig, Aretha (2017) Structure and function of HWE/HisKA2-family sensor histidine kinases. Curr Opin Microbiol 36:47-54
Willett, Jonathan W; Crosson, Sean (2017) Atypical modes of bacterial histidine kinase signaling. Mol Microbiol 103:197-202
Eaton, Daniel S; Crosson, Sean; Fiebig, Aretha (2016) Proper Control of Caulobacter crescentus Cell Surface Adhesion Requires the General Protein Chaperone DnaK. J Bacteriol 198:2631-42
Meyer, Peter A; Socias, Stephanie; Key, Jason et al. (2016) Data publication with the structural biology data grid supports live analysis. Nat Commun 7:10882
Fiebig, Aretha; Herrou, Julien; Willett, Jonathan et al. (2015) General Stress Signaling in the Alphaproteobacteria. Annu Rev Genet 49:603-25
Herrou, Julien; Willett, Jonathan W; Crosson, Sean (2015) Structured and Dynamic Disordered Domains Regulate the Activity of a Multifunctional Anti-? Factor. MBio 6:e00910

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