Sucrose dependent mineral phosphate solubilization in Enterobacter asburiae PSI3 by heterologous overexpression of periplasmic invertases.

Abstract

Enterobacter asburiae PSI3 solubilizes mineral phosphates in the presence of glucose by the secretion of gluconic acid generated by the action of a periplasmic pyrroloquinoline quinone dependent glucose dehydrogenase. In order to achieve mineral phosphate solubilization phenotype in the presence of sucrose, plasmids pCNK4 and pCNK5 containing genes encoding the invertase enzyme of Zymomonas mobilis (invB) and of Saccharomyces cerevisiae (suc2) under constitutive promoters were constructed with malE signal sequence (in case of invB alone as the suc2 is secreted natively). When introduced into E. asburiae PSI3, E. a. (pCNK4) and E. a. (pCNK5) transformants secreted 21.65±0.94 and 22±1.3mM gluconic acid, respectively, in the presence of 75mM sucrose and they also solubilized 180±4.3 and 438±7.3µM P from the rock phosphate. In the presence of a mixture of 50mM sucrose and 25mM glucose, E. a. (pCNK5) secreted 34±2.3mM gluconic acid and released 479±8.1µM P. Moreover, in the presence of a mixture of eight sugars (10mM each) in the medium, E. a. (pCNK5) released 414±5.3µM P in the buffered medium. Thus, this study demonstrates incorporation of periplasmic invertase imparted P solubilization ability to E. asburiae PSI3 in the presence of sucrose and mixture of sugars.