Research article

Global transcriptional responses of Pseudomonas syringae DC3000 to changes in iron bioavailability in vitro

Philip A Bronstein^1,2 , Melanie J Filiatrault^1,2 , Christopher R Myers³ , Michael Rutzke⁴ , David J Schneider^1,2 and Samuel W Cartinhour^1,2

¹United States Department of Agriculture-Agricultural Research Service, Robert W Holley Center for Agriculture and Health, Ithaca, NY 14853, USA

²Department of Plant Pathology and Plant-Microbe Biology, Cornell University, Ithaca, NY 14853, USA

³Computational Biology Service Unit, Life Sciences Core Laboratories Center, Cornell University, Ithaca, NY 14852, USA

⁴Department of Food Science, Cornell University, Ithaca, NY 14853, USA

author email corresponding author email

BMC Microbiology 2008, 8:209doi:10.1186/1471-2180-8-209

Published:	2 December 2008

Abstract

Background

Pseudomonas syringae pv tomato DC3000 (DC3000) is a Gram-negative model plant pathogen that is found in a wide variety of environments. To survive in these diverse conditions it must sense and respond to various environmental cues. One micronutrient required for most forms of life is iron. Bioavailable iron has been shown to be an important global regulator for many bacteria where it not only regulates a wide variety of genes involved in general cell physiology but also virulence determinants. In this study we used microarrays to study differential gene regulation in DC3000 in response to changes in levels of cell-associated iron.

Results

DC3000 cultures were grown under highly controlled conditions and analyzed after the addition of iron citrate or sodium citrate to the media. In the cultures supplemented with iron, we found that cell-associated iron increased rapidly while culture densities were not significantly different over 4 hours when compared to cultures with sodium citrate added. Microarray analysis of samples taken from before and after the addition of either sodium citrate or iron citrate identified 386 differentially regulated genes with high statistical confidence. Differentially regulated genes were clustered based on expression patterns observed between comparison of samples taken at different time points and with different supplements. This analysis grouped genes associated with the same regulatory motifs and/or had similar putative or known function.

Conclusion

This study shows iron is rapidly taken up from the medium by iron-depleted DC3000 cultures and that bioavailable iron is a global cue for the expression of iron transport, storage, and known virulence factors in DC3000. Furthermore approximately 34% of the differentially regulated genes are associated with one of four regulatory motifs for Fur, PvdS, HrpL, or RpoD.