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Review ARTICLE

Front. Microbiol., 18 July 2011 | http://dx.doi.org/10.3389/fmicb.2011.00155

Protein secretion systems in Pseudomonas aeruginosa: an essay on diversity, evolution, and function

  • Division of Cell and Molecular Biology, Centre for Molecular Microbiology and Infection, Imperial College London, London, UK

Protein secretion systems are molecular nanomachines used by Gram-negative bacteria to thrive within their environment. They are used to release enzymes that hydrolyze complex carbon sources into usable compounds, or to release proteins that capture essential ions such as iron. They are also used to colonize and survive within eukaryotic hosts, causing acute or chronic infections, subverting the host cell response and escaping the immune system. In this article, the opportunistic human pathogen Pseudomonas aeruginosa is used as a model to review the diversity of secretion systems that bacteria have evolved to achieve these goals. This diversity may result from a progressive transformation of cell envelope complexes that initially may not have been dedicated to secretion. The striking similarities between secretion systems and type IV pili, flagella, bacteriophage tail, or efflux pumps is a nice illustration of this evolution. Differences are also needed since various secretion configurations call for diversity. For example, some proteins are released in the extracellular medium while others are directly injected into the cytosol of eukaryotic cells. Some proteins are folded before being released and transit into the periplasm. Other proteins cross the whole cell envelope at once in an unfolded state. However, the secretion system requires conserved basic elements or features. For example, there is a need for an energy source or for an outer membrane channel. The structure of this review is thus quite unconventional. Instead of listing secretion types one after each other, it presents a melting pot of concepts indicating that secretion types are in constant evolution and use basic principles. In other words, emergence of new secretion systems could be predicted the way Mendeleïev had anticipated characteristics of yet unknown elements.

Keywords: cell envelope, nanomachine, macromolecular complex, channel, targeting

Citation: Filloux A (2011) Protein secretion systems in Pseudomonas aeruginosa: an essay on diversity, evolution, and function. Front. Microbio. 2:155. doi: 10.3389/fmicb.2011.00155

Received: 26 April 2011; Paper pending published: 25 May 2011;
Accepted: 01 July 2011; Published online: 18 July 2011.

Edited by:

Dara Frank, Medical College of Wisconsin, USA

Reviewed by:

Maria Sandkvist, University of Michigan, USA
Katrina Forest, University of Wisconsin-Madison, USA

Copyright: © 2011 Filloux. This is an open-access article subject to a non-exclusive license between the authors and Frontiers Media SA, which permits use, distribution and reproduction in other forums, provided the original authors and source are credited and other Frontiers conditions are complied with.

*Correspondence: Alain Filloux, Division of Cell and Molecular Biology, Centre for Molecular Microbiology and Infection, Imperial College London, South Kensington Campus, Flowers Building, SW72AZ London, UK. e-mail: a.filloux@imperial.ac.uk