Phosphate-Solubilizing Microorganisms of a Lateritic Soil: I. Solubilization of Inorganic Phosphates and Production of Organic Acids by Microorganisms, Isolated in Sucrose Calcium Phosphate Agar Plates

Abstract

Summary Among twenty phosphate-solubilizing microorganisms, isolated in sucrose calcium phosphate agar plates from a representative Indian lateritic soil (Typic Ochragualf), nine were bacteria of the genus Bacillus, six actinomycetes of the genus Streptomyces, and five were fungi, four of the genua Aspergillus and one Penicillium. Of these, the efficient phosphate-solubilizers were LCB1 — Bacillus firmus (B-7647), LCB9 — a mixed culture of B. circulans and B. subtilis (B-7648), LCS4 — Streptomyces sp., LCF1 — Penicillium sp., LCF3 — an unreported species of Aspergillus and LCF4 — A. niger van Tieghem. In general, the solubilization was highest from Ca3(PO4)2, followed by that from AlPO4 and FePO4. In this respect, the overall efficiency of the genera was in the order Bacillus, Penicillium, Aspergillus, and Streptomyces. The organic acids produced by the above organisms in sucrose calcium phosphate broth were 2-ketogluconic, oxalic, succinic, malonic acids, and an unidentified one. Although there was no correlation between the production of organic acids and solubilization of phosphorus, the isolates producing 2-ketogluconic acid together with succinic acid showed higher ability of solubilizing insoluble inorganic phosphates.