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Front. Cell. Infect. Microbiol. | doi: 10.3389/fcimb.2018.00054

Extracellular actin is a receptor for Mycoplasma hyopneumoniae

Benjamin B. Raymond1, Ranya Madhkoor1, Ina Schleicher2,  Cord C. Uphoff3, Lynne Turnbull1,  Cynthia B. Whitchurch1,  Manfred Rohde2,  Matthew P. Padula1, 4 and  Steven P. Djordjevic1*
  • 1The ithree Institute, University of Technology Sydney, Australia
  • 2Central Facility for Microscopy, Helmholtz Centre for Infection Research, Germany
  • 3Deutsche Sammlung von Mikroorganismen und Zellkulturen (DSMZ), Germany
  • 4Proteomics Core Facility, University of Technology Sydney, Australia

Mycoplasma hyopneumoniae, an agriculturally important porcine pathogen, disrupts the mucociliary escalator causing ciliostasis, loss of cilial function and epithelial cell death within the porcine lung. Losses to swine production due to growth rate retardation and reduced feed conversion efficiency are severe, and antibiotics are used heavily to control mycoplasmal pneumonia. Notably, little is known about the repertoire of host receptors that M. hyopneumoniae targets to facilitate colonisation. Here we show, for the first time, that actin exists extracellularly on porcine epithelial monolayers (PK-15) using surface biotinylation and 3D-Structured Illumination Microscopy (3D-SIM), and that M. hyopneumoniae binds to the extracellular β-actin exposed on the surface of these cells. Consistent with this hypothesis we show: i) monoclonal antibodies that target β-actin significantly block the ability of M. hyopneumoniae to adhere and colonise PK-15 cells; ii) microtitre plate binding assays show that M. hyopneumoniae cells bind to monomeric G-actin in a dose dependent manner; iii) more than 100 M. hyopneumoniae proteins were recovered from affinity-chromatography experiments using immobilised actin as bait; and iv) biotinylated monomeric actin binds directly to M. hyopneumoniae proteins in ligand blotting studies. Specifically, we show that the P97 cilium adhesin possesses at least two distinct actin-binding regions, and binds monomeric actin with nanomolar affinity. Taken together, these observations highlight that actin may be an important receptor for M. hyopneumoniae within the swine lung and will aid in the future development of intervention strategies against this devastating pathogen. Furthermore, they also have wider implications for extracellular actin as an important bacterial receptor.

Keywords: Extracellular actin, Mycoplasma Infections, Host-Pathogen Interactions, Adhesins, Bacterial, super resolution microscopy

Received: 29 Nov 2017; Accepted: 12 Feb 2018.

Edited by:

Yinduo Ji, University of Minnesota Twin Cities, United States

Reviewed by:

Alexis Bonfim-Melo, Federal University of São Paulo, Brazil
Maria Rapala-Kozik, Jagiellonian University, Poland  

Copyright: © 2018 Raymond, Madhkoor, Schleicher, Uphoff, Turnbull, Whitchurch, Rohde, Padula and Djordjevic. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Prof. Steven P. Djordjevic, University of Technology Sydney, The ithree Institute, PO Box 123, Broadway, Ultimo, 2007, Australia,