School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York 14853, USA.
Biotechnol Bioeng. 2010 Apr 1;105(5):955-64. doi: 10.1002/bit.22609.
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.
采用恒化器培养系统研究模式植物病原菌丁香假单胞菌 pv.番茄 DC3000 的生长，以研究环境调节响应。使用以铁为限制营养的最小培养基，在定制的连续培养系统中获得了四种不同类型的响应：（1）稳定的稳态，（2）阻尼振荡，（3）由于高稀释率超过最大生长率而导致的正常冲洗，以及（4）由于负生长率而导致的低稀释率冲洗。响应类型由初始细胞质量和稀释率的组合决定。稳定的稳态是在稀释率为 0.059 至 0.086 h(-1) 且初始细胞质量小于 0.6 OD(600)的范围内获得的。阻尼振荡和负生长率是细菌系统的异常观察结果。我们在初始细胞质量为 0.9 OD(600)或更高，或无论初始细胞质量如何，稀释率较低（<0.05 h(-1))时观察到这些响应。这种响应表明存在复杂的动力学，包括可能存在多个稳态。铁早些时候被报道为一种广泛使用的最小培养基中的生长限制营养物，与未补充对照相比，在补充铁的培养物中，它既能增强生长又能增强毒力因子的诱导。在分批和恒化器培养中，细胞内铁浓度与毒力因子的早期诱导（6 h）相关。与补充铁的恒化器培养相比，在铁限制的恒化器培养中观察到 aconitase 活性（三羧酸循环酶）和 ATP 水平降低，表明铁影响中央代谢途径。我们得出结论，DC3000 培养物特别依赖于环境，铁可能是决定生理学的关键营养物。
