Short Communication

Subject Category: Microbial population and community ecology

The ISME Journal (2009) 3, 632–634; doi:10.1038/ismej.2009.9; published online 19 February 2009

Siderophore production and biofilm formation as linked social traits

Freya Harrison1 and Angus Buckling1

1Department of Zoology, University of Oxford, Oxford, UK

Correspondence: F Harrison, Current address: Department of Biology and Biochemistry, University of Bath, Claverton Down, Bath BA2 7AY, UK. E-mail:

Received 12 January 2009; Accepted 13 January 2009; Published online 19 February 2009.



The virulence of pathogenic microbes can depend on individual cells cooperating in the concerted production of molecules that facilitate host colonization or exploitation. However, cooperating groups can be exploited by social defectors or ‘cheats’. Understanding the ecology and evolution of cooperation is therefore relevant to clinical microbiology. We studied two genetically linked cooperative traits involved in host exploitation by the opportunistic human pathogen Pseudomonas aeruginosa. Clones that defected from cooperative production of iron-scavenging siderophores were deficient in biofilm formation. The presence of such clones in mixed biofilms with a wild-type clone led to reduced biofilm mass. The fitness advantage of siderophore-deficient mutants in the presence of wild-type bacteria was no greater in biofilm than in planktonic culture, suggesting that these mutants did not gain an additional advantage by exploiting wild-type biofilm polymer. Reduced biofilm formation therefore represents a pleiotropic cost of defection from siderophore production.


biofilm, cooperation, cystic fibrosis, iron, Pseudomonas aeruginosa, siderophores


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