Glucose and arabinose dependent mineral phosphate solubilization and its succinate-mediated catabolite repression in Rhizobium sp. RM and RS

Abstract

Rhizobium sp. RM and RS are Vigna radiata root nodule isolates with the ability to solubilize tricalcium phosphate and rock phosphate under 50mM Tris-Cl buffering conditions. Rhizobium sp. RM and RS were unique as they could produce two different organic acids, gluconic acid and oxalic acid using glucose and arabinose, respectively, which are two of the most prominent sugars present in the rhizospheric soil. However, P solubilization in these isolates was repressed in the presence of succinate resembling the phenomenon of catabolite repression. RM and RS produced 24mM and 20mM gluconic acid in presence of glucose which was repressed to 10mM and 8mM, respectively, in glucose + succinate conditions. Similarly, RM and RS produced 28mM and 23mM oxalic acid in arabinose containing media which was repressed to 9mM and 8mM, respectively, in the presence of arabinose+succinate. Results of enzyme activities indicated 66% repression of quinoprotein glucose dehydrogenase in glucose + succinate compared to glucose grown cells and 84% repression of glyoxylate oxidase in arabinose+succinate compared to arabinose grown cells. This is perhaps the first report on mechanism of P solubilization in rhizobia through utilization of two different sugars, glucose and arabinose and its repression by succinate. Succinate-mediated catabolite repression of arabinose is the unique aspect of this study.