Mascher Fabio, Schnider-Keel Ursula, Haas Dieter, Défago Geneviève, Moënne-Loccoz Yvan
Phytopathology Group, Institute of Plant Science, Swiss Federal Institute of Technology (ETH), CH-8092 Zürich, Switzerland.
Environ Microbiol. 2003 Feb;5(2):103-15. doi: 10.1046/j.1462-2920.2003.00388.x.
Certain fluorescent pseudomonads can protect plants from soil-borne pathogens, and it is important to understand how these biocontrol agents survive in soil. The persistence of the biocontrol strain Pseudomonas fluorescens CHA0-Rif under plough pan conditions was assessed in non-sterile soil microcosms by counting total cells (immunofluorescence microscopy), intact cells (BacLight membrane permeability test), viable cells (Kogure's substrate-responsiveness test) and culturable cells (colony counts on selective plates) of the inoculant. Viable but non-culturable cells of CHA0-Rif (106 cells g-1 soil) were found in flooded microcosms amended with fermentable organic matter, in which the soil redox potential was low (plough pan conditions), in agreement with previous observations of plough pan samples from a field inoculated with CHA0-Rif. However, viable but non-culturable cells were not found in unamended flooded, amended unflooded or unamended unflooded (i.e. control) microcosms, suggesting that such cells resulted from exposure of CHA0-Rif to a combination of low redox potential and oxygen limitation in soil. CHA0-Rif is strictly aerobic. Its anaerobic regulator ANR is activated by low oxygen concentrations and it controls production of the biocontrol metabolite hydrogen cyanide under microaerophilic conditions. Under plough pan conditions, an anr-deficient mutant of CHA0-Rif and its complemented derivative displayed the same persistence pattern as CHA0-Rif, indicating that anr was not implicated in the formation of viable but non-culturable cells of this strain at the plough pan.
某些荧光假单胞菌能够保护植物免受土传病原体的侵害，因此了解这些生物防治剂如何在土壤中存活非常重要。通过对接种剂的总细胞（免疫荧光显微镜法）、完整细胞（BacLight膜通透性测试）、活细胞（小暮氏底物反应性测试）和可培养细胞（选择性平板上的菌落计数）进行计数，在非无菌土壤微观世界中评估了生物防治菌株荧光假单胞菌CHA0-Rif在犁底层条件下的持久性。在添加了可发酵有机物的淹水微观世界中发现了CHA0-Rif的活但不可培养细胞（106个细胞 g-1土壤），其中土壤氧化还原电位较低（犁底层条件），这与之前对接种了CHA0-Rif的田间犁底层样品的观察结果一致。然而，在未添加有机物的淹水、添加有机物的非淹水或未添加有机物的非淹水（即对照）微观世界中未发现活但不可培养细胞，这表明此类细胞是CHA0-Rif暴露于土壤中低氧化还原电位和氧气限制的组合导致的。CHA0-Rif是严格需氧的。其厌氧调节因子ANR被低氧浓度激活，并在微需氧条件下控制生物防治代谢产物氰化氢的产生。在犁底层条件下，CHA0-Rif的anr缺陷突变体及其互补衍生物表现出与CHA0-Rif相同的持久性模式，表明anr与该菌株在犁底层形成活但不可培养细胞无关。
