title: Blue-Light Inhibition of Listeria monocytogenes Growth Is Mediated by Reactive Oxygen Species and Is Influenced by σB and the Blue-Light Sensor Lmo0799.
abstract: Listeria monocytogenes senses blue light via the flavin mononucleotide-containing sensory protein Lmo0799, leading to activation of the general stress response sigma factor SigB (σ(B)). In this study, we investigated the physiological response of this foodborne pathogen to blue light. We show that blue light (460 to 470 nm) doses of 1.5 to 2 mW cm(-2) cause inhibition of growth on agar-based and liquid culture media. The inhibitory effects are dependent on cell density, with reduced effects evident when high cell numbers are present. The addition of 20 mM dimethylthiourea, a scavenger of reactive oxygen species, or catalase to the medium reverses the inhibitory effects of blue light, suggesting that growth inhibition is mediated by the formation of reactive oxygen species. A mutant strain lacking σ(B) (ΔsigB) was found to be less inhibited by blue light than the wild type, likely indicating the energetic cost of deploying the general stress response. When a lethal dose of light (8 mW cm(-2)) was applied to cells, the ΔsigB mutant displayed a marked increase in sensitivity to light compared to the wild type. To investigate the role of the blue-light sensor Lmo0799, mutants were constructed that either had a deletion of the gene (Δlmo0799) or alteration in a conserved cysteine residue at position 56, which is predicted to play a pivotal role in the photocycle of the protein (lmo0799 C56A). Both mutants displayed phenotypes similar to the ΔsigB mutant in the presence of blue light, providing genetic evidence that residue 56 is critical for light sensing in L. monocytogenes Taken together, these results demonstrate that L. monocytogenes is inhibited by blue light in a manner that depends on reactive oxygen species, and they demonstrate clear light-dependent phenotypes associated with σ(B) and the blue-light sensor Lmo0799.
  
  
  
  Listeria monocytogenes is a bacterial foodborne pathogen that can cause life-threatening infections in humans. It is known to be able to sense and respond to visible light. In this study, we examine the effects of blue light on the growth and survival of this pathogen. We show that growth can be inhibited at comparatively low doses of blue light, and that at higher doses, L. monocytogenes cells are killed. We present evidence suggesting that blue light inhibits this organism by causing the production of reactive oxygen species, such as hydrogen peroxide. We help clarify the mechanism of light sensing by constructing a "blind" version of the blue-light sensor protein. Finally, we show that activation of the general stress response by light has a negative effect on growth, probably because cellular resources are diverted into protective mechanisms rather than growth.
authors.affiliation: Bacterial Stress Response Group, Microbiology, School of Natural Sciences, National University of Ireland, Galway, Galway, Ireland.
authors.forename: Beth
authors.initials: B
authors.lastname: O'Donoghue
authors.affiliation: Bacterial Stress Response Group, Microbiology, School of Natural Sciences, National University of Ireland, Galway, Galway, Ireland.
authors.forename: Kerrie
authors.initials: K
authors.lastname: NicAogáin
authors.affiliation: National Centre for Laser Applications, School of Physics, National University of Ireland, Galway, Galway, Ireland.
authors.forename: Claire
authors.initials: C
authors.lastname: Bennett
authors.affiliation: National Centre for Laser Applications, School of Physics, National University of Ireland, Galway, Galway, Ireland.
authors.forename: Alan
authors.initials: A
authors.lastname: Conneely
authors.affiliation: Department of Molecular Biology, Molecular Infection Medicine, Sweden, and Umeå Centre for Microbial Research, Umeå University, Umeå, Sweden.
authors.forename: Teresa
authors.initials: T
authors.lastname: Tiensuu
authors.affiliation: Department of Molecular Biology, Molecular Infection Medicine, Sweden, and Umeå Centre for Microbial Research, Umeå University, Umeå, Sweden.
authors.forename: Jörgen
authors.initials: J
authors.lastname: Johansson
authors.affiliation: Bacterial Stress Response Group, Microbiology, School of Natural Sciences, National University of Ireland, Galway, Galway, Ireland conor.obyrne@nuigalway.ie.
authors.forename: Conor
authors.initials: C
authors.lastname: O'Byrne
mesh_terms: D000900:Anti-Bacterial Agents / Q000633:toxicity*; D003470:Culture Media / Q000737:chemistry; D005420:Flavoproteins / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial; D008027:Light; D008089:Listeria monocytogenes / Q000254:growth & development / Q000502:physiology* / Q000528:radiation effects*; D017354:Point Mutation; D017382:Reactive Oxygen Species / Q000633:toxicity*; D012808:Sigma Factor / Q000235:genetics / Q000378:metabolism*
chemical_list: D000900:Anti-Bacterial Agents; D003470:Culture Media; D005420:Flavoproteins; D017382:Reactive Oxygen Species; C480945:SigB protein, Listeria monocytogenes; D012808:Sigma Factor