No abstract

No abstract

In vitro gluconic acid formation and phosphate solubilization from sparingly soluble phosphorus sources by two strains of the plant growth-promoting bacteria A. brasilense (Cd and 8-I) and one strain of A. lipoferum JA4 were studied. Strains of A. brasilense were capable of producing gluconic acid when grown in sparingly soluble calcium phosphate medium when their usual fructose carbon source is amended with glucose. At the same time, there is a reduction in pH of the medium and release of soluble phosphate. To a greater extent, gluconic acid production and pH reduction were observed for A. lipoferum JA4. For the three strains, clearing halos were detected on solid medium plates with calcium phosphate. This is the first report of in vitro gluconic acid production and direct phosphate solubilization by A. brasilense and the first report of P solubilization by A. lipoferum. This adds to the very broad spectrum of plant growth-promoting abilities of this genus.

Plant growth-promoting bacteria (PGPB) are soil and rhizosphere bacteria that can benefit plant growth by different mechanisms. The ability of some microorganisms to convert insoluble phosphorus (P) to an accessible form, like orthophosphate, is an important trait in a PGPB for increasing plant yields. In this mini-review, the isolation and characterization of genes involved in mineralization of organic P sources (by the action of enzymes acid phosphatases and phytases), as well as mineral phosphate solubilization, is reviewed. Preliminary results achieved in the engineering of bacterial strains for improving capacity for phosphate solubilization are presented, and application of this knowledge to improving agricultural inoculants is discussed.

No abstract