PRODUCTION OF ORGANIC ACID AND SOLUBILIZATION OF INORGANIC PHOSPHATE BY A BACTERIUM ISOLATED FROM CONTAMINATED SOIL

Abstract

Many agricultural soils have significant phosphorus (P) reserves, much of which builds up because of frequent P fertilizer applications. However, roughly 95 to 99% of soil phosphorus is found as insoluble phosphates and is therefore unavailable for plant uptake. The current investigation characterized a bacterial strain that was obtained from contaminated soil and showed the ability to solubilize insoluble inorganic phosphates. An efficient phosphate-solubilizing bacterium was isolated in polluted soil in Mumbai. The phosphate solubilization index of this isolate was assessed using tribasic calcium phosphate-supplemented Pikovskaya’s (PVK) medium. After growing under constant agitation for seven days, the medium pH decreased from 7.0 to 3.5 units. Based on the colony morphology, microscopic analysis, and MALDI-TOF sequencing, the bacterial isolate was identified as Klebsiella pneumoniae. Phosphate solubilization was linked to a pH drop caused by bacterial growth in a medium with glucose as a carbon source. The secretion of organic acids by these phosphate-solubilizing bacteria is responsible for their ability to solubilize inorganic phosphate. GC-MS analysis revealed the presence of carbamic acid, dodecanoic acid, tetra decanoic acid, and trifluoroacetic acid in the culture supernatant. The amount of phosphate solubilized by the bacterium was determined by phosphomolybdate assay and was found to be 667.0 ug/ml which was much higher than the control bacterium S. aureus which was 131.0 ug/ml. To the best of our knowledge, this is the first report mentioning the isolation of phosphate solubilizing bacterium from polluted soil in Mumbai.