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Direct Gas Sensing and Repellent Response to Toxic Gases in Anaerobic Pathogens

Hespen, Charles W
Scripps Research Institute
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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 HNOX-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.
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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.
Funding Source
Nat'l. Inst. of General Medical Sciences
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Bacterial Pathogens
Escherichia coli
Chemical Contaminants