Cell culturability of Pseudomonas protegens CHA0 depends on soil pH.
Pseudomonas inoculants may lose colony-forming ability in soil, but soil properties involved are poorly documented. Here, we tested the hypothesis that soil acidity could reduce persistence and cell culturability of Pseudomonas protegens CHA0. At 1 week in vitro, strain CHA0 was found as culturable cells at pH 7, whereas most cells at pH 4 and all cells at pH 3 were noncultured. In 21 natural soils of contrasted pH, cell culturability loss of P. protegens CHA0 took place in all six very acidic soils (pH < 5.0) and in three of five acidic soils (5.0 < pH < 6.5), whereas it was negligible in the neutral and alkaline soils at 2 weeks and 2 months. No correlation was found between total cell counts of P. protegens CHA0 and soil composition data, whereas colony counts of the strain correlated with soil pH. Maintenance of cell culturability in soils coincided with a reduction in inoculant cell size. Some of the noncultured CHA0 cells were nutrient responsive in Kogure's viability test, both in vitro and in soil. Thus, this shows for the first time that the sole intrinsic soil composition factor triggering cell culturability loss in P. protegens CHA0 is soil acidity.
Plant Pathology, Institute of Integrative Biology, Swiss Federal Institute of Technology, Zürich, Switzerland; Agroscope Changins-Wädenswil research station ACW, Nyon, Switzerland.
Fabio
F
Mascher
Carsten
C
Hase
Marie-Lara
ML
Bouffaud
Geneviève
G
Défago
Yvan
Y
Moënne-Loccoz
D058491:Bacterial Load; D001431:Bacteriological Techniques; D018929:Cell Culture Techniques; D006863:Hydrogen-Ion Concentration; D011549:Pseudomonas / Q000254:growth & development*; D012987:Soil / Q000737:chemistry*; D012988:Soil Microbiology
D012987:Soil
Pseudomonas; biocontrol; cell culturability; soil acidity; survival