Pseudomonas fluorescens pirates both ferrioxamine and ferri-coelichelin siderophores from Streptomyces ambofaciens. J Galet, A Deveau, L Hôtel, P Frey-Klett, P Leblond, B Aigle. Applied and Environmental Microbiology, AEM. 03520-14

ABSTRACT

Iron is essential in many biological processes. However, its bioavailability is reduced in aerobic environments such as soil. To overcome this limitation, microorganisms have developed different strategies, such as iron chelation by siderophores. Some bacteria have even gained the ability to detect and utilize xenosiderophores, i.e. siderophores produced by other organisms. We illustrate an example of such an interaction between two soil bacteria, Pseudomonas fluorescens strain BBc6R8 and Streptomyces ambofaciens ATCC23877, which produce the siderophores pyoverdine and enantio-pyochelin and the siderophores desferrioxamines B, E and coelichelin, respectively. During pairwise cultures on iron-limiting agar medium, no induction of siderophore synthesis byP. fluorescens BBc6R8 was observed in presence of S. ambofaciens ATCC23877. Co-cultures with a Streptomyces mutant strain that produced either coelichelin or desferrioxamines, as well as culture in a medium supplemented with desferrioxamine B, resulted in the absence of pyoverdine production; however, culture with a double mutant deficient in desferrioxamines and coelichelin production did not. This strongly suggests that P. fluorescens BBbc6R8 utilizes the ferrioxamines and ferri-coelichelin produced by S. ambofaciens as xenosiderophores, and therefore no longer activates the production of its own siderophores. A screening of a library of P. fluorescens BBc6R8 mutants highlighted the involvement of the TonB-dependent receptor FoxA in this process: the expression of foxA and genes involved in the regulation of its biosynthesis was induced in presence of S. ambofaciens. In a competitive environment such as soil, siderophore piracy could well be one of the driving forces that determines the outcome of microbial competition.