SCREENING OF PHOSPHATE SOLUBILIZING BACTERIA FROM SOILS OF DHARAN, SUNSARI, NEPAL

Phosphorus is one of the essential macronutrients for plant growth and reproduction. Plant absorbs phosphorus from soil solution as phosphate anions which are highly reactive and may be immobilized by precipitation with cations such as Ca²⁺, Mg²⁺, Fe³⁺ and Al³⁺, present in the soil and thus it becomes insoluble and unavailable for plants. PSB can be used as biofertilizer since they increase phosphorus availability in the soil for growing plants. The main objective of this study was to isolate and identify PSB morphologically and biochemically from the agricultural soil sample. For this purpose, total 16 samples were collected. Isolation was performed on Pikovskaya’s (PVK) media by spread plate technique. PSB were isolated from soil sample of Dharan, taken from agricultural field. The isolated organisms were identified according to colony morphology, gram staining reactions and various biochemical properties. The solubilization index (SI) and solubilization efficiency (SE) were calculated on the basis of the halozone and colony diameter. Only two PSB were isolated. Both were gram positive, spore forming rod shaped bacteria. According to colony characteristics, staining reactions and biochemical tests, the isolates were Bacillus megaterium and Streptomyces spp. Their phosphate solubilizing ability was analyzed qualitatively on PVK plate. Their solubilizing indexes (SI) were found to be 1.75 and 1.33 while solubilizing efficiency (SE) were calculated 75% and 33% respectively. Both PSB isolates were spore former, as the soils of Dharan generally contain comparatively low moisture (drought) in April to June.