African Journal of Biotechnology Vol. 5 (10), pp. 850-854, 16 May 2006   

ISSN 1684–5315 © 2006 Academic Journals        

Full Length Research Paper

Solubilization of inorganic phosphates by fungi isolated from agriculture soil

N Pradhan*, and LB Sukla

Regional Research Laboratory, Bhubaneswar, Orissa, India.

*Corresponding Author  E-mail: npradhan@rrlbhu.res.in , nilotpala_pradhan@yahoo.co.in.

Accepted 11 May, 2005

Abstract

Most agricultural soils contain large reserves of phosphorus (P), a considerable part of which accumulates as a consequence of regular applications of P fertilizers. However, a greater part of soil phosphorus, approximately 95–99% is present in the form of insoluble phosphates and hence cannot be utilized by the plants. In the present study fungal strains isolated from agriculture soil, having potential to solubilize insoluble inorganic phosphates were characterized. Two fungal isolates were tested for their tricalcium phosphate (TCP) solubilization efficiency in both solid and liquid medium. Isolates were identified as Aspergillus sp. and Penicillium sp. depending upon their colony morphology and microscopic studies. Phosphate solubilization was related to pH decrease caused by growth of fungus in medium containing glucose as carbon source. Aspergillus sp. solubilized 480 μg/ml of phosphorus, while Penicillium sp. solubilized 275 μg/ml of phosphorus from 0.5% tricalcium phosphate after 4 and 3 days of growth respectively. Both the strains show diverse levels of phosphate solubilization activity in liquid broth culture in presence of various carbon and nitrogen sources. Drop in pH during growth was more prominent in absence of TCP in the liquid medium. This indicates that absence of soluble P in media induces the acid production. Phosphate solubilizing microorganisms convert insoluble phosphates into soluble forms generally through the process of acidification, chelation and exchange reactions. Thus such microorganisms may not only compensate for higher cost of manufacturing fertilizers in industry but also mobilizes the fertilizers added to soil.

Key words: Tricalcium phosphate, phosphate solubilization, Aspergillus, Penicillium