Complex responses to culture conditions in Pseudomonas syringae pv. tomato DC3000 continuous cultures: the role of iron in cell growth and virulence factor induction.
The growth of a model plant pathogen, Pseudomonas syringae pv. tomato DC3000, was investigated using a chemostat culture system to examine environmentally regulated responses. Using minimal medium with iron as the limiting nutrient, four different types of responses were obtained in a customized continuous culture system: (1) stable steady state, (2) damped oscillation, (3) normal washout due to high dilution rates exceeding the maximum growth rate, and (4) washout at low dilution rates due to negative growth rates. The type of response was determined by a combination of initial cell mass and dilution rate. Stable steady states were obtained with dilution rates ranging from 0.059 to 0.086 h(-1) with an initial cell mass of less than 0.6 OD(600). Damped oscillations and negative growth rates are unusual observations for bacterial systems. We have observed these responses at values of initial cell mass of 0.9 OD(600) or higher, or at low dilution rates (<0.05 h(-1)) irrespectively of initial cell mass. This response suggests complex dynamics including the possibility of multiple steady states.Iron, which was reported earlier as a growth limiting nutrient in a widely used minimal medium, enhances both growth and virulence factor induction in iron-supplemented cultures compared to unsupplemented controls. Intracellular iron concentration is correlated to the early induction (6 h) of virulence factors in both batch and chemostat cultures. A reduction in aconitase activity (a TCA cycle enzyme) and ATP levels in iron-limited chemostat cultures was observed compared to iron-supplemented chemostat cultures, indicating that iron affects central metabolic pathways. We conclude that DC3000 cultures are particularly dependent on the environment and iron is likely a key nutrient in determining physiology.
Kim
Beum Jun
BJ
School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York 14853, USA.
Schneider
David J
DJ
Cartinhour
Samuel W
SW
Shuler
Michael L
ML
D000154:Aconitate Hydratase / Q000378:metabolism; D001426:Bacterial Proteins / Q000378:metabolism; D003470:Culture Media / Q000737:chemistry; D007501:Iron / Q000378:metabolism*; D044224:Pseudomonas syringae / Q000254:growth & development* / Q000378:metabolism* / Q000472:pathogenicity; D037521:Virulence Factors / Q000378:metabolism*
D001426:Bacterial Proteins; D003470:Culture Media; D037521:Virulence Factors; D007501:Iron; D000154:Aconitate Hydratase