10.3390/microorganisms9010173 Chlamydia Uses K⁺ Electrical Signalling to Orchestrate Host Sensing, Inter-Bacterial Communication and Differentiation Andrew Susan C. Dr. Institute of Structural and Molecular Biology, University College London & Birkbeck, Malet Street, London WC1E 7HX, UK Mint Diagnostics, Unit 1093b Kent Science Park, Sittingbourne ME9 8GA, UK susan.clements@mintdiagnostics.com http://orcid.org/0000-0002-1732-1041 Dumoux Maud Dr. Institute of Structural and Molecular Biology, University College London & Birkbeck, Malet Street, London WC1E 7HX, UK Rosalind Franklin Institute, Harwell Campus, Didcot OX11 0DE, UK maud.dumoux@rfi.ac.uk http://orcid.org/0000-0002-1710-2172 Hayward Richard D. Dr. Institute of Structural and Molecular Biology, University College London & Birkbeck, Malet Street, London WC1E 7HX, UK Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QP, UK rdh24@cam.ac.uk 15 01 2021 9 1 08 01 2021 e173 Prokaryotic communities coordinate quorum behaviour in response to external stimuli to control fundamental processes including inter-bacterial communication. The obligate intracellular bacterial pathogen Chlamydia adopts two developmental forms, invasive elementary bodies (EBs) and replicative reticulate bodies (RBs), which reside within a specialised membrane-bound compartment within the host cell termed an inclusion. The mechanisms by which this bacterial community orchestrates different stages of development from within the inclusion in coordination with the host remain elusive. Both prokaryotic and eukaryotic kingdoms exploit ion-based electrical signalling for fast intercellular communication. Here we demonstrate that RBs specifically accumulate potassium (K⁺) ions, generating a gradient. Disruption of this gradient using ionophores or an ion-channel inhibitor stalls the Chlamydia lifecycle, inducing persistence. Using photobleaching approaches, we establish that the RB is the master regulator of this [K⁺] differential and observe a fast K⁺ exchange between RBs revealing a role for this ion in inter-bacterial communication. Finally, we demonstrate spatio-temporal regulation of bacterial membrane potential during RB to EB differentiation within the inclusion. Together, our data reveal that Chlamydia harnesses K⁺ to orchestrate host sensing, inter-bacteria communication and pathogen differentiation. Medical Research Council MR L008696/1 © 1996-2021 MDPI (Basel, Switzerland) 2021 This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited Chlamydia host-pathogen interactions cell-to-cell communications and community Microorganisms Microorganisms 2076-2607 MDPI