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

item Bronstein, Philip
item Filiatrault, Melanie
item Moll, Monica
item Schneider, David
item Cartinhour, Samuel

Submitted to: American Society for Microbiology
Publication Type: Abstract Only
Publication Acceptance Date: 6/13/2007
Publication Date: 8/26/2007
Citation: Bronstein, P., Filiatrault, M.J., Kim, B., Moll, M., Rutzke, M., Shuler, M., Schneider, D.J., Cartinhour, S.W. 2007. Global transcriptional responses of Pseudomonas syringae DC3000 to changes in iron bioavailability in vitro. American Society for Microbiology. p. 20.

Interpretive Summary:

Technical Abstract: Pseudomonas syringae pv. tomato DC3000 (DC3000) is a model bacterial pathogen of tomato and Arabidopsis thaliana. Understanding the environmental conditions and genetic mechanisms that control the expression of virulence-related genes is a central for understanding how this phytopathogen causes disease. In this study we examined the transcriptional changes of DC3000 grown in iron-limited and iron-replete minimal media. We found that iron is a limiting reagent in minimal media, which supports expression of known virulence factors in DC3000. Additionally, we found by qRT-PCR that the addition of iron to the media resulted in increased expression of many virulence-related genes, including type III secretion system and phytotoxin biosynthetic pathways. To examine the global regulatory effects that iron exerts on DC3000, we monitored changes in transcription in a shift from iron-limited to iron-replete growth conditions. In order to focus the analysis on the effects of iron and minimize other growth effects, we optimized culture conditions for batch growth in a bioreactor system to tightly monitor and/or control temperature, pH, and dissolved O2.. In these experiments either iron citrate or sodium citrate was added to logarithmically growing cultures of DC3000 in iron-limited minimal media and samples were taken at 30 minutes and four hours after the addition of the supplements. Iron levels in the media and the bacterial pellets from each time point were measured by inductively-coupled plasma emission spectrometry (ICP-ES). RNA was isolated from the cultures, processed, and analyzed using Affymetrix-style oligo arrays from NimbleGen. In addition, intracellular iron levels were correlated to the transcriptional activity of these cultures. The microarray analysis confirmed the iron-dependent expression of siderophores, putative TonB-dependent siderophore receptors, virulence-related genes as well as identified differential expression of several ECF-type sigma factors, two-component regulatory systems and a number of uncharacterized genes. From this study we conclude that iron in an important mediator of gene expression in the plant pathogen P. syringae pv. tomato DC3000.