|Kim, Beum Jun - CORNELL UNIV|
|Park, Joon Ho - CORNELL UNIV|
|Park, Tai Hyun - CORNELL UNIV|
|Shuler, Michael - CORNELL UNIV|
Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 27, 2009
Publication Date: May 1, 2009
Citation: Kim, B., Park, J., Park, T., Bronstein, P., Schneider, D.J., Cartinhour, S.W., Shuler, M.L. 2009. Iron concentration limits growth rate and the expression of virulence factors in hrp-inducing minimal medium with Pseudomonas syringae. Applied and Environmental Microbiology. 25(9):2720-2726. Interpretive Summary: Specific growth conditions have been developed to induce pathogens to produce disease-causing proteins. However specific signals (or components) are difficult to directly link to the production of the proteins. By using a specialized bacterial growth apparatus, we found that iron is a limiting nutrient for growth in the standard virulence inducing minimal medium and plays an important role in inducing the production of disease-causing proteins in Pseudomonas syringae pv. tomato DC3000. With various concentrations of iron, growth was found to follow simple Monod-type kinetics for low to moderate iron concentrations. Iron began to be toxic at higher levels. We found that the kinetics of the production of disease-causing proteins gene can be expressed mathematically in terms of iron concentration. We conclude that studies of induction disease-causing proteins in P. syringae should monitor and control iron levels carefully to reduce variations in the availability of this essential nutrient.
Technical Abstract: Although chemically-defined media have been developed and widely used to study the expression of virulence factors in the model plant pathogen, Pseudomonas syringae, it has been difficult to link specific medium components to the induction response. Using a chemostat system, we found that iron is the limiting nutrient for growth in the standard hrp-inducing minimal medium and plays an important role in inducing several virulence-related genes in Pseudomonas syringae pv. tomato DC3000. With various concentrations of iron oxalate, growth was found to follow Monod-type kinetics for low to moderate iron concentrations. Observable toxicity due to iron began at 800 µM Fe3+. The kinetics of virulence factor gene induction can be expressed mathematically in terms of supplemented iron concentration. We conclude that studies of induction of virulence-related genes in P. syringae should control iron levels carefully to reduce variations in the availability of this essential nutrient.