Cell culturability of P seudomonas protegens CHA 0 depends on soil p H

P seudomonas 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 P seudomonas protegens CHA 0. At 1 week in vitro , strain CHA 0 was found as culturable cells at p H 7, whereas most cells at p H 4 and all cells at p H 3 were noncultured. In 21 natural soils of contrasted p H , cell culturability loss of P . protegens CHA 0 took place in all six very acidic soils (p H < 5.0) and in three of five acidic soils (5.0 < p H  < 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 CHA 0 and soil composition data, whereas colony counts of the strain correlated with soil p H . Maintenance of cell culturability in soils coincided with a reduction in inoculant cell size. Some of the noncultured CHA 0 cells were nutrient responsive in K ogure'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 CHA 0 is soil acidity.