Potential phosphate solubilizing bacteria from the rhizosphere of Cotylelobium melanoxylon tree

Microorganism have important roles in soil cycles and plant living activities. Phosphate solubilizing bacteria is one of the microorganisms in the soil that plays a role in helping provide phosphorus nutrients that are not available to plants. The purpose of this study was to obtain potential phosphate solubilizing bacteria from the rhizosphere Cotylelobium melanoxylon plants. Soil samples were taken in a composite at a depth of 0-20 cm from the rhizosphere area of C. melanoxylon plants in the village of Bona Lumban, Tukka District, Tapanuli Tengah Regency, North Sumatra. Isolation of phosphate solubilizing bacteria using the dilution plate technique with Pikovskaya medium. Phosphate solubilizing bacterial isolates were selected qualitatively by measuring the ratio of the clear zone. Selected isolates are identified up to species molecularly. The isolation results obtained were 16 isolates of phosphate solubilizing bacteria with a clear zone ratio varying between 1.03 to 1.68. Four isolates were selected with the highest clear zone ratio. Based on molecular identification, the four isolates included Pseudomonas aeruginosa species.