The effect of Pseudomonas fluorescens strains varying in psoverdine production on the soil redox status

Abstract

The ability of a pyoverdine producing Pseudomonas fluorescens strain C7R12 to act as an effector of soil redox status was determined using as control an isogenic mutant which does not produce pyoverdine (strain PL1). During the period of observation (68 h), the redox potential of the soil inoculated with strain C7R12 was higher than that of the soil inoculated with the mutant PLI. The soil pH at 68 h decreased in the following order: control soil >inoculated soil with strain PL1> inoculated soil with strain C7R12 (p < 0.05). The redox capacity of soil-EDTA extracts was measured after 68 h with differential pulse polarography. The quantity of electroactive compounds within the potentials range studied (+300 to -900 mV) differed among treatments. The soil inoculated with strain C7R12 exhibited a lower concentration of electroactive compounds in lower potentials (+30 mV to -330 mV), and a higher concentration in higher potentials (around +170 mV) than the soil inoculated with mutant strain PL1. This explains the difference observed in redox potential values between inoculated soils. In the noninoculated soil, the redox potential was higher, and the redox capacity lower (within the potentials range studied) than in the inoculated soils. Taking into account that the soil extract used excludes the presence of inorganic ions in the soil solution, we conclude that the effect of strain C7R12 on the soil redox status would involve more complex mechanisms than the sequestering of iron by the pyoverdine, probably associated with the presence of organic electroactive compounds.