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Open Access Research article

Photorhabdus adhesion modification protein (Pam) binds extracellular polysaccharide and alters bacterial attachment

Robert T Jones15, Maria Sanchez-Contreras1*, Isabella Vlisidou1, Matthew R Amos1, Guowei Yang1, Xavier Muñoz-Berbel2, Abhishek Upadhyay1, Ursula J Potter3, Susan A Joyce16, Todd A Ciche4, A Toby A Jenkins2, Stefan Bagby1, Richard H ffrench-Constant15 and Nicholas R Waterfield1

  • * Corresponding author: Maria Sanchez-Contreras msc23@bath.ac.uk

  • † Equal contributors

Author Affiliations

1 Department of Biology and Biochemistry, University of Bath, Claverton Down, Bath, BA2 7AY, UK

2 Department of Chemistry, University of Bath, Claverton Down, Bath, BA2 7AY, UK

3 Centre for Electron Optical Studies, University of Bath, Claverton Down, Bath, BA2 7AY, UK

4 Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, 48824, USA

5 School of Biosciences, University of Exeter in Cornwall, Penryn, TR10 9EZ, UK

6 Department of Microbiology, University College Cork, Cork, Republic of Ireland

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BMC Microbiology 2010, 10:141  doi:10.1186/1471-2180-10-141

Published: 12 May 2010

Abstract

Background

Photorhabdus are Gram-negative nematode-symbiotic and insect-pathogenic bacteria. The species Photorhabdus asymbiotica is able to infect humans as well as insects. We investigated the secreted proteome of a clinical isolate of P. asymbiotica at different temperatures in order to identify proteins relevant to the infection of the two different hosts.

Results

A comparison of the proteins secreted by a clinical isolate of P. asymbiotica at simulated insect (28°C) and human (37°C) temperatures led to the identification of a small and highly abundant protein, designated Pam, that is only secreted at the lower temperature. The pam gene is present in all Photorhabdus strains tested and shows a high level of conservation across the whole genus, suggesting it is both ancestral to the genus and probably important to the biology of the bacterium. The Pam protein shows limited sequence similarity to the 13.6 kDa component of a binary toxin of Bacillus thuringiensis. Nevertheless, injection or feeding of heterologously produced Pam showed no insecticidal activity to either Galleria mellonella or Manduca sexta larvae. In bacterial colonies, Pam is associated with an extracellular polysaccharide (EPS)-like matrix, and modifies the ability of wild-type cells to attach to an artificial surface. Interestingly, Surface Plasmon Resonance (SPR) binding studies revealed that the Pam protein itself has adhesive properties. Although Pam is produced throughout insect infection, genetic knockout does not affect either insect virulence or the ability of P. luminescens to form a symbiotic association with its host nematode, Heterorhabditis bacteriophora.

Conclusions

We studied a highly abundant protein, Pam, which is secreted in a temperature-dependent manner in P. asymbiotica. Our findings indicate that Pam plays an important role in enhancing surface attachment in insect blood. Its association with exopolysaccharide suggests it may exert its effect through mediation of EPS properties. Despite its abundance and conservation in the genus, we find no evidence for a role of Pam in either virulence or symbiosis.