Efficiency of three Pseudomonas isolates in releasing phosphate from an artificial variable-charge mineral (iron III hydroxide)

Phosphorus management in agriculture involves acquiring exact and comprehensive information about the fate of added phosphate to the soil. A great part of a phosphate (P) fertiliser is retained on the surface of variable charge minerals through specific adsorption; the precipitation process takes place in the limited space around the fertiliser grains where its concentration is high. We tested the ability of three Pseudomonas strains to release P frim iron (III) hydroxide. Iron hydroxide precipitated on filter paper, was used a variable-charge mineral and P was loaded on it. The siderophore and H+ production, acid and alkaline phosphatases activity were assayed in vitro. All three isolates released P as compared to controls with killed bacteria or without bacteria. The amount of released P from iron hydroxide were 50.5, 29.2 and 61.6% for P. putida, P.fluorescens Chao and P. fluorescens Tabriz, respectively. The amount of P in solution phase was highest (0.74 mg P/50mL) with P. putida and lowest (0.32 mg P/50 mL) with P. fluorescens Tabriz The highest P assimilation from total P released was in P. fluorescens Tabriz. In vitro tests revealed that the P. fluorescens Chao with significantly higher siderophore production and phosphatases activity, had the least effect on P release from iron hydroxide, while two other isolates had significantly higher H+ production is the main mechanism of P released from variable charge minerals and P.putida was the most efficient bacterium.