Studies on microbial isolates for phosphorus solubilization

Abstract

Soil microorganisms play a vital role in maintaining the ecological balance by activeparticipation in Carbon, Nitrogen, Sulphur, Phosphorus and Potassium cycles in nature.Phosphate solubilising microbes plays an important role in plant nutrition through increase in phosphate uptake by plants and is used as bio fertilizers in agricultural crops. Phosphate issecond most vital macronutrient required for the growth and development of plants. Thephosphorous solubilising microorganisms (PSMs) are rhizospheric microorganism which solubilises the insoluble phosphorous(P) to soluble forms of Phosphorous for plant growth and yield. It is therefore of great interest to investigate management strategies that are capable of improving phosphorus fertilization efficiency, which reflects in higher crop yields and reduce environmental pollution caused by phosphorus loss from the soil. Phosphorous is such an important macronutrient which is very often present in the soil in unavailable form. Phosphorus, both native in soil and applied to inorganic fertilizers becomes mostly unavailable to crops because of its low level of mobility and solubility and its tendency to become fixed in soil. Many soil bacteria particularly those belonging to the genera Bacillus and Pseudomonas posses the ability to bring insoluble phosphates in the soluble forms by secreting organic acids. These acids lower the pH and bring about the dissolution of bound forms of phosphorous. These bacteria are commonly known as phosphor bacteria. They can be applied either through seed or soil application. During the current study isolation of twentyfive different Pseudomonasisolates from various soilsamples and their identification on the basis of Gram staining, colony morphology andbiochemical tests. Gram positive rod shaped bacteria showing large, circular, opaque colonieshaving bluish white/sea green/blue appearance were preserved on Kings B slant for further identification tests. Mximum isolates showed positive results and some showed negative results for citrate utilization test,MR test, VP Test, Nitrate reduction test and TSI tests. Phosphate solubilisation activities of different isolates was performed. Out of twenty five isolates, sixteen isolates solubilised phosphate on Pikovskaya’s agar medium at 30°C after 10 days of incubation (Sample code 1, 2, 4, 5A, 7C1a, 7C1b, 8, 9, 14, 15, 16, 17, 19, 20, X, S.S). In these isolates clear visible zone of P solublization was observed. Among all studied isolates namely sample codes 1, 7C1a, 7C1b 8, 9, 17, 19, X, S.S showed significantly higher phosphorous solubilisation.