Bacterial pathogens possess elaborate mechanisms to sense and avoid chemical hazards. One important mechanism in environmental sensing is chemotaxis, a two-component signaling pathway responsible for directional change in bacterial swimming. Recently, methyl-accepting chemotaxis proteins (MCP) fused to Heme Nitric oxide/Oxygen (H-NOX) sensor domains were identified through genomic analyses of the obligate anaerobic pathogens Clostridium botulinum and Clostridium tetani. Ubiquitous in biology, H-NOX domains are found in organisms from bacteria to mammals. A molecular understanding of ligand binding has been established. However, the signal propagation mechanisms of these domains in obligate anaerobic bacteria are still unknown. Previously characterized gas-sensing chemotaxis proteins respond indirectly to gases. For example, Aer, the oxygen sensor in E. coli, senses changes in cytosolic reduction potential as oxygen concentration changes. The H-NOX-MCP may act as a heretofore-uncharacterized direct gas sensor in which the H-NOX domain binds small concentrations of ligand and induces a panic evasion response in bacteria. In this research plan, signal output and ligand sensitivity of the H NOX-MCP protein will be investigated in the presence of oxygen or nitric oxide. To understand the mechanism of signal transmission, the molecular interactions between H-NOX and MCP domains will also be studied. Finally, in vivo chemotaxis experiments will be performed on wild type and H-NOX-MCP mutants of Clostridium sporogenes, a close relative to C. botulinum, to understand how the organism responds to steadily increasing concentrations of oxygen and nitric oxide. This investigation will expand knowledge of bacterial two-component signaling as well as characterize a novel mechanism for toxic gas sensing common to pathogenic species of Clostridium.

Public Health Relevance

Design of new antibiotics to stem the rising tide of resistant bacterial pathogens requires a molecular level understanding of novel bacterial signaling pathways. Chemotaxis, a signaling pathway that affects bacterial locomotion in response to outside stimulus, is ubiquitous in nearly all bacteria. Here, a specific chemotaxis mechanism found in the foodborne pathogen, Clostridium botulinum, that senses small amounts of toxic diatomic gases will be investigated.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Predoctoral Individual National Research Service Award (F31)
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Special Emphasis Panel (ZRG1-F04-K (09))
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Gaillard, Shawn R
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Scripps Research Institute
La Jolla
United States
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Hespen, Charles W; Bruegger, Joel J; Phillips-Piro, Christine M et al. (2016) Structural and Functional Evidence Indicates Selective Oxygen Signaling in Caldanaerobacter subterraneus H-NOX. ACS Chem Biol 11:2337-46