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      Soluble electron shuttles can mediate energy taxis toward insoluble electron acceptors.

      Environmental Science & Technology

      Chemotaxis, drug effects, Computer Simulation, Electron Transport, Electrons, Manganese Compounds, pharmacology, Models, Biological, Oxides, Thermodynamics, Riboflavin, Shewanella, cytology, growth & development, Solubility, Biological Assay

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          Abstract

          Shewanella species grow in widely disparate environments and play key roles in elemental cycling, especially in environments with varied redox conditions. To obtain a system-level understanding of Shewanella's robustness and versatility, the complex interplay of cellular growth, metabolism, and transport under conditions of limiting carbon sources, energy sources, and electron acceptors must be elucidated. In this paper, population-level taxis of Shewanella oneidensis MR-1 cells in the presence of a rate-limiting, insoluble electron acceptor was investigated. A novel mechanism, mediated energy taxis, is proposed by which Shewanella use riboflavin as both an electron shuttle and an attractant to direct cell movement toward local sources of insoluble electron acceptors. The cells secrete reduced riboflavin, which diffuses to a nearby particle containing an insoluble electron acceptor and is oxidized. The oxidized riboflavin then diffuses away from the particle, establishing a spatial gradient that draws cells toward the particle. Experimental and modeling results are presented to support this mechanism. S. oneidensis MR-1 cells inoculated into a uniform dispersion of MnO(2) particles in dilute agar exhibited taxis outward, creating a clear zone within which riboflavin was detected by mass spectrometry. Cells inoculated into dilute agar containing oxidized riboflavin similarly exhibited taxis, rapidly forming an expanding zone of reduced riboflavin. A mathematical model based on the proposed mechanism was able to predict experimental trends, including how concentrations of riboflavin and insoluble electron acceptors (e.g., MnO(2)) affected tactic cell migration.

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          Author and article information

          Journal
          22324484
          10.1021/es204302w

          Comments

          added an editorial note to Shewanella

          How do Shewanella find their way to an insoluble electron acceptor? Being insoluble, it won't release any species for chemotactic receptors to interact with. Li et al examine the possibility that flavins, water soluble electron transfer mediators produced and released by Shewanella, may in their oxidized form also serve the bacteria to sense the proximity of insoluble electron sinks.

          2016-03-11 16:49 UTC
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