CONICET | Buscador de Institutos y Recursos Humanos

Commonly used protocols for in-vitro detection of plant growth promoting (PGP) features were develops for bacteria. Using these protocols for yeast´s in-vitro screening is sometimes difficult and the results are no always reliable. The aim of the present study is to develop easy, fast and affordable method to perform large scale screening to evaluate in-vitro PGP characteristics on yeast. Four yeasts strains from different taxonomical groups were evaluated and known bacterial strain CHA0 was used control.Phosphate solubilization ability was tested on Pikovskaya medium, commonly used for bacteria, and three media commonly used for yeast, containing 0.5% of HCaPO4. All cultures were incubated at 20°C and examined daily for 1 week. Semi-quantitative determination was performed comparing colony and halo diameter. Yeasts were able to grow in all media, but yeast medium LEV allowed a better halo identification after 72hs, for all tested strains, than Pikovskaya medium. Siderophores production was evaluated using CAS method, on solid and liquid MMS medium (Schwyn & Neilands; 1987). All cultures were incubated at 20°C, plates were examined weekly for 1 month and liquid cultures were tested after 12 days of growth. Yeast growth inhibition was observed when using cell suspension on NaCl 0.8%; the use of tooth-pick is recommended for plate´s inoculation. Detection of siderophores in culture supernatant was successfully achieved using the absorbance spectrum instead of single reading at 630nm suggested by Schwyn & Neilands (1987). The proposed methods were successfully used on representative isolates from 29 species yeast from different taxonomical groups. Several species shown the ability to solubilize phosphate or produce siderophores. The maximum value for phosphate solubilization was 250% and the maximum value for siderophores production was 8.5mM.