title: Exposure to static magnetic field stimulates quorum sensing circuit in luminescent Vibrio strains of the Harveyi clade.
abstract: In this study, the evidence of electron-dense magnetic inclusions with polyhedral shape in the cytoplasm of Harveyi clade Vibrio strain PS1, a bioluminescent bacterium living in symbiosis with marine organisms, led us to investigate the behavior of this bacterium under exposure to static magnetic fields ranging between 20 and 2000 Gauss. When compared to sham-exposed, the light emission of magnetic field-exposed bacteria growing on solid medium at 18°C ±0.1°C was increased up to two-fold as a function of dose and growth phase. Stimulation of bioluminescence by magnetic field was more pronounced during the post-exponential growth and stationary phase, and was lost when bacteria were grown in the presence of the iron chelator deferoxamine, which caused disassembly of the magnetic inclusions suggesting their involvement in magnetic response. As in luminescent Vibrio spp. bioluminescence is regulated by quorum sensing, possible effects of magnetic field exposure on quorum sensing were investigated. Measurement of mRNA levels by reverse transcriptase real time-PCR demonstrated that luxR regulatory gene and luxCDABE operon coding for luciferase and fatty acid reductase complex were significantly up-regulated in magnetic field-exposed bacteria. In contrast, genes coding for a type III secretion system, whose expression was negatively affected by LuxR, were down-regulated. Up-regulation of luxR paralleled with down-regulation of small RNAs that mediate destabilization of luxR mRNA in quorum sensing signaling pathways. The results of experiments with the well-studied Vibrio campbellii strain BB120 (originally classified as Vibrio harveyi) and derivative mutants unable to synthesize autoinducers suggest that the effects of magnetic fields on quorum sensing may be mediated by AI-2, the interspecies quorum sensing signal molecule.
authors: Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali, Università del Salento, Lecce, Italy.
authors: Adelfia
authors: A
authors: Talà
authors: Dipartimento di Matematica e Fisica "Ennio De Giorgi", Università del Salento INFN - Lecce, Lecce, Italy.
authors: Domenico
authors: D
authors: Delle Side
authors: Dipartimento di Matematica e Fisica "Ennio De Giorgi", Università del Salento INFN - Lecce, Lecce, Italy.
authors: Giovanni
authors: G
authors: Buccolieri
authors: Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali, Università del Salento, Lecce, Italy.
authors: Salvatore Maurizio
authors: SM
authors: Tredici
authors: Dipartimento di Matematica e Fisica "Ennio De Giorgi", Università del Salento INFN - Lecce, Lecce, Italy.
authors: Luciano
authors: L
authors: Velardi
authors: Dipartimento di Matematica e Fisica "Ennio De Giorgi", Università del Salento INFN - Lecce, Lecce, Italy.
authors: Fabio
authors: F
authors: Paladini
authors: Dipartimento di Scienze Ambientali, Seconda Università di Napoli, Caserta, Italy.
authors: Mario
authors: M
authors: De Stefano
authors: Dipartimento di Matematica e Fisica "Ennio De Giorgi", Università del Salento INFN - Lecce, Lecce, Italy.
authors: Vincenzo
authors: V
authors: Nassisi
authors: Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali, Università del Salento, Lecce, Italy.
authors: Pietro
authors: P
authors: Alifano
mesh_terms: D005798:Genes, Bacterial; D008163:Luminescent Measurements; D060526:Magnetic Fields; D009154:Mutation; D053038:Quorum Sensing; D014733:Vibrio / Q000235:genetics / Q000378:metabolism / Q000502:physiology*