Submitted to: BMC Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/2/2008
Publication Date: 12/2/2008
Citation: Bronstein, P., Filiatrault, M.J., Myers, C., Rutzke, M., Schneider, D.J., Cartinhour, S.W. 2008. Global transcriptional responses of Pseudomonas syringae DC3000 to changes in iron bioavailability in vitro. BMC Microbiology. 8:209. Interpretive Summary: Pseudomonas syringae pv. tomato DC3000 (DC3000) is an important bacterial pathogen of tomato. Understanding the environmental conditions that tell the bacteria when to cause disease is essential to allow us to control this pathogen. In this study we examined how DC3000 reacts to the amount of iron in its environment. The bacterium was grown under highly controlled conditions and levels of iron in the environment and inside the bacteria were measured. We looked at culture samples before, 30 minutes and four hours after the addition of either iron citrate or sodium citrate. We found that the bacteria reacted quickly to the levels of iron in the environment by expressing pathways to take-up and store iron as well as to start production of disease causing proteins. Additionally we found that the bacteria produced many proteins that were of unknown function. We were able to group all observed changes by looking for similar patterns of their presence in the bacteria. We found that proteins involved in similar processes generally grouped together with elements that are known, or suspected, to control these processes. We believe that these analyses are useful in identifying the function of proteins with previously unknown functions and will help us identify how the bacteria controls these proteins.
Technical Abstract: Pseudomonas syringae pv. tomato DC3000 (DC3000) is a model bacterial pathogen of tomato and Arabidopsis. Understanding the environmental conditions 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. DC3000 cultures were grown under highly controlled conditions in bioreactors and iron levels in the media and the bacterial pellets from were measured by inductively-coupled plasma emission spectrometry (ICP-ES). We took samples before, 30 minutes and four hours after the addition of either iron citrate or sodium citrate. To examine the global regulatory effects that iron exerts on DC3000, we monitored changes in transcription using Affymetrix-style oligo arrays from NimbleGen. The microarray analysis confirmed the iron-dependent expression of siderophores, putative TonB-dependent siderophore receptors, virulence-related genes as well as the differential expression of many known or putative regulator elements, including ECF-type sigma factors and two-component regulators as well as many uncharacterized genes. By clustering genes based on their differential expression between various time points and conditions, we were able to group genes with similar regulatory patterns and putative functions. We then applied previously derived bioinformatic regulator motifs for ferric uptake regulator, and the sigma factors HrpL, PvdS, and RpoD found upstream of differentially regulated genes. These motifs also grouped together in the clustering analysis; thereby implying that this analysis also clustered genes controlled by the same regulatory elements.