|Quecine, Maria Carolina|
Submitted to: Biometals
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/18/2010
Publication Date: 2/2/2011
Citation: Hartney, S., Mazurier, S., Kidarsa, T.A., Quecine, M., Lemanceau, P., Loper, J.E. 2011. TonB-Dependent outer-membrane proteins and siderophore utilization in Pseudomonas fluorescens Pf-5. Biometals. 24(2):193. Interpretive Summary: Biological control is a promising and environmentally-friendly approach for the management of plant diseases in agriculture. We study the biological control agent Pseudomonas fluorescens strain Pf-5, a soil bacterium that can protect seeds and roots from infection by pathogens that live in the soil. This paper describes a study focused on a specific class of proteins that play a role in the acquisition of nutrients, especially iron, by strain Pf-5. The full genomic sequence of Pf-5 was obtained several years ago, and we used that sequence to identify all of the proteins in this class and compare them to others now available in nucleotide sequence data bases. Those comparisons allowed us to assign possible functions to many of the proteins. We then did experiments in the laboratory to confirm that Pf-5 has several of those predicted functions. This study is important because it provides an overview of a class of proteins that bacteria use to acquire resources from the environment. In order to suppress plant pathogens, biological control agents like Pf-5 must be able to establish populations on plant surfaces. To do this, they have to acquire resources that are in short supply on plant surfaces. This study provided new insight into the way that Pf-5 acquires limiting resources from the environment.
Technical Abstract: The soil bacterium Pseudomonas fluorescens Pf-5 produces two siderophores, a pyoverdine and enantio-pyochelin, and its proteome includes 45 TonB-dependent outer-membrane proteins, which commonly function in uptake of siderophores and other substrates from the environment. The 45 proteins share the conserved receptor and plug domains of TonB-dependent proteins but only 18 of them have an N-terminal signaling domain characteristic of TonB-dependent transducers (TBDTs), which participate in cell-surface signaling systems. Phylogenetic analyses of the 18 TBDTs and 25 TonB-dependent receptors (TBDRs), which lack the N-terminal signaling domain, suggest a complex evolutionary history including horizontal transfer among different microbial lineages. Putative functions were assigned to certain TBDRs and TBDTs in clades including well-characterized orthologs from other Pseudomonas spp. A mutant of Pf-5 deficient in pyoverdine and enantio-pyochelin production was constructed and characterized for iron-limited growth and utilization of a spectrum of siderophores. The mutant could utilize as iron sources a large number of pyoverdines with diverse structures as well as ferric citrate, heme, and the siderophores ferrichrome, ferrioxamine B, enterobactin, and aerobactin. The diversity and complexity of the TBDTs and TBDRs with roles in iron uptake clearly indicate the importance of iron in the fitness and survival of Pf-5 in the environment.