2-Ketogluconic Acid Secretion by Incorporation of Pseudomonas putida KT 2440 Gluconate Dehydrogenase (gad) Operon in Enterobacter asburiae PSI3 Improves Mineral Phosphate Solubilization

Abstract

Enterobacter asburiae PSI3 is known to efficiently solubilize rock phosphate by secretion of approximately50mM gluconic acid in Tris-buffered medium in the presence of 75mM glucose and in a mixture of seven aldosugars each at 15mM concentration, mimicking alkaline vertisol soils. Efficacy of this bacterium in the rhizosphere requires P release in the presence of low amount of sugars. To achieve this, E. asburiae PSI3 has been manipulated to express gluconate dehydrogenase (gad) operon of Pseudomonas putida KT 2440 to produce 2-ketogluconic acid. E. asburiae PSI3 harboring gad operon had 438U of GAD activity, secreted 11.63mM 2-ketogluconic and 21.65mM gluconic acids in Tris-rock phosphate-buffered medium containing 45mM glucose. E. asburiae PSI3 gad transformant solubilized 0.84mM P from rock phosphate in TRP-buffered liquid medium. In the presence of a mixture of seven sugars each at 12mM, the transformant brought about a drop in pH to 4.1 and released 0.53mM P.