MPS(Mineral Phosphate Solubilisation) Phenotype & its Repression by Succinate in Acinetobactersp

Abstract

Soil consists of abundant nutrients which are required by plants for their growth. Plant growth promoting bacteria (PGPB) are the important part of plant soil interaction. Specifically Rhizosphere soil where most of the PGPB resides, is a complex consortia of various biochemical products exuded by plant roots and from bacteria also. This provides PGPB a huge environmental variation for their survival and symbiosis with the plant. As Rhizosphere soil contains various exudates from plant roots, carbon catabolite repression (CCR) must play an important role for bacterial physiology. CCR may have effect on the preferential utilization of glucose or the organic acid production as, glucose is the best carbon source known for organic acid production linked P solubilization. Phosphate is required by plants in large amounts for growth and development. We looked for mineral phosphate solubilizing Acinetobacter, considering it has two forms of glucose dehydrogenase: one membrane bound and other soluble, both responsible for phosphate solubilisation. Four isolates K2, SN2, 10 & 14 were characterized biochemically and molecularly as Acinetobacter species. Isolate K2 and SN2 were studied for mineral phosphate solubilisation. Maximum TCP and RP was solubilised was 469.7 μg/ml and 20.4 μg/ml respectively, thus making isolate K2 the potential phosphate solubilizer. Furthermore production of gluconic acid (20mM) was confirmed by HPLC. But when effect of various carbon sources on phosphate solubilization by this isolate was checked, repression of MPS phenotype was observed in presence of succinate. This means the PSB will fail in field conditions. Hence, Succinate mediated catabolite repression (SMCR) was studied by performing enzyme assays for both mGDH and sGDH in repressed (Glucose+Succinate) and non-repressed (Glucose) conditions, which showed that enzyme activity was maximum in presence of glucose while in presence of succinate it was repressed. Diauxic growth profile showed that succinate was preferentially utilized over glucose. Expression studies carried out for both the enzymes in presence of glucose and succinate correlates with the enzyme activities and the gdhA and gdhB repressed in presence of succinate. The whole study gave a new outlook to understand biochemical and molecular mechanism of mineral phosphate solubilisation and it’s CCR by succinate.