Isolation and characterization of phosphate solubilizing actinomycetes from rhizosphere soil

Abstract EN

Eighteen actinomycetes strains were isolated from rhizosphere soils taken from experimental farm of faculty of agriculture, Assiut University, Egypt, planted with wheat, faba bean and clover.

Out of the 18 isolates, 9 (50 %) showed an ability to solubilize inorganic phosphates, based on inducing clear zones around their colonies growing on a tricalcium phosphate medium after incubation for 10 days at 28 °C.

The phosphate solubilization index of strains A1, A2, A3, A4, A5, A7, A8, A10 and A18 on pikovskaya,s modified agar medium were 3.40, 2.40, 2.57, 4.50, 3.10, 1.57, 2.10, 3.83 and 1.83, respectively.

The highest phosphate solubilization index was recorded by the strain A4 and the lowest by the strain A7.

The isolates were further studied for ability to solubilize phosphorus from insoluble phosphate in Pikovskaya,s liquid medium containing tricalcium phosphate.

Amounts of phosphorus solubilized by the actinomycete strains A1, A2, A3, A4, A5, A7, A8, A10 and A18 were 52, 45, 46, 78, 32, 37, 36, 55 and 45 mg/100 ml culture, respectively.

The highest amount of P solubilized (78 mg/100 ml culture) was recorded for the actinomycetes strain A4, which showed the highest of phosphate solubilization index (4.5) and the lowest pH (4.00) in a 10- day liquid culture medium.

The solubilized amounts of P and the determined phosphate solubilization index for the actinomycete isolates are compatible with the acidity (pH values) produced in their cultures.

This indicates that the organic acids produced from fermentation of sugars in the media by actinomycete isolates are the main cause of solubilization.

Nine phosphate solubilizing actinomycete isolates were identified on the basis of colony characteristics, microscopic observation and biochemical test.

All nine isolates of actinomycetes were observed to be from the genus Streptomyces.