Electrolocation? The evidence for redox‐mediated taxis in Shewanella oneidensis

• Published in: Molecular microbiology Vol. 115; no. 6; pp. 1069 - 1079
• Main Authors: Starwalt‐Lee, Ruth, El‐Naggar, Mohamed Y., Bond, Daniel R., Gralnick, Jeffrey A.
• Format: Journal Article
• Language: English
• Published: Oxford Blackwell Publishing Ltd 01.06.2021
• Subjects: Cell migration; Chemotaxis; Circuits; dissimilatory iron reduction; Electrolocation; Electron transfer; Energy gradient; energy taxis; Flavin; Genomes; Shewanella oneidensis; Signal transduction; Taxis
• ISSN: 0950-382X; 1365-2958
• DOI: 10.1111/mmi.14647

Shewanella oneidensis is a dissimilatory metal reducing bacterium and model for extracellular electron transfer (EET), a respiratory mechanism in which electrons are transferred out of the cell. In the last 10 years, migration to insoluble electron acceptors for EET has been shown to be nonrandom and tactic, seemingly in the absence of molecular or energy gradients that typically allow for taxis. As the ability to sense, locate, and respire electrodes has applications in bioelectrochemical technology, a better understanding of taxis in S. oneidensis is needed. While the EET conduits of S. oneidensis have been studied extensively, its taxis pathways and their interplay with EET are not yet understood, making investigation into taxis phenomena nontrivial. Since S. oneidensis is a member of an EET‐encoding clade, the genetic circuitry of taxis to insoluble acceptors may be conserved. We performed a bioinformatic analysis of Shewanella genomes to identify S. oneidensis chemotaxis orthologs conserved in the genus. In addition to the previously reported core chemotaxis gene cluster, we identify several other conserved proteins in the taxis signaling pathway. We present the current evidence for the two proposed models of EET taxis, “electrokinesis” and flavin‐mediated taxis, and highlight key areas in need of further investigation. Shewanella oneidensis migrates to insoluble oxide minerals and electrodes non‐randomly to respire by extracellular electron transfer—a behavior that cannot be readily explained by current models of bacterial taxis. In this MicroReview, we discuss what is known about taxis in S. oneidensis, highlight complexities of chemotaxis‐related pathways in these bacteria and propose strategies to further our understanding of a novel taxis mechanism.