Pseudomonas cepacia–Mediated Rock Phosphate Solubilization in Kaolinite and Montmorillonite Suspensions

Abstract

Pseudomonas cepacia is known as a rock phosphate (RP) solubilizer in bioreactors and in soils. The objectives of this study were to determine the production rates of gluconic acid (GA, pKd 3.41) and 2‐ketogluconic acid (KGA, pKd 2.66) by the bacteria in the presence of clay minerals which prevail in soils, and the resulting rate and extent of orthophosphate (OP) release into the suspension solutions. Suspensions (1:40) of RP, RP + Ca–kaolinite (CaKL), RP + Ca–montmorillonite (CaMT), and RP + K–montmorillonite (KMT) were inoculated with P. cepacia E37. The electrical conductivity (EC) and pH, and the OP, glucose, GA, KGA, Ca, and Al concentrations were determined in the suspension solutions as functions of time. In a given clay system, the rate‐limiting step in RP dissolution was the rate of GA release by the E37. This acid lowered the pH of all the clay suspensions to 2.7 to 2.8, which resulted in a pronounced increase in the OP concentration in solution, Cp. As glucose was depleted from the system, the KGA concentration increased with a concomitant lowering in pH to ≈2.5. At this pH, a sharp decline in Cp occurred, which was attributed to Al release by the alumosilicates, and formation of a new, stable Al–P or Fe–P solid phase. The E37 glucose oxidation efficiency (GOE) was considerably inhibited in CaKL as compared with CaMT or KMT. The GA and KGA adsorption by the clays or their Ca complexation did not play a role in the E37‐mediated RP solubilization.

Bioactivation of phosphate rocks by indigenous phosphate-solubilizing fungi Bioaktivasi fosfat alam oleh fungi pelarut fosfat setempat

“…The efficacy of selected Pseudomonas species in dissolving PR from suspension, agar, and soil has received considerable attention in the last two decades. Bar-Yosef et al (1999) confirmed that gluconic and 2ketogluconic' acids produced by P. cepacia increased the orthophosphate concentration in solution.…”

Isolation and characterization of plant growth-promoting rhizobacteria from wheat rhizosphere and their effect on plant growth promotion

“…In two different studies, very limited number of P-solubilizers (23.5% of the total tested strains and five out of the 207 isolates) has been reported (Hameeda et al, 2006; Islam et al, 2010). The soil phosphate solubilizing strains can increase the availability of phosphorus to plant by mineralizing organic phosphorus compounds and by converting inorganic phosphorus into more available form (Bar-Yosef et al, 1999). Phosphate solubilization is mainly due to the production of microbial metabolites including organic acids which decreases the pH of the culture media (Puente et al, 2004; Sahin et al, 2004; Shahid et al, 2012).…”

Isolation, characterization and beneficial effects of rice associated plant growth promoting bacteria from Zanzibar soils

“…Earlier studies expressed that a number of phosphate solubilizing bacterial strains showed an effective role in P-uptake and growth promotion of plants by dissolution of inorganic insoluble phosphate (BELIMOV et al 1995, DAS andMUKHERJEE 2000). The soil microorganism (PBS strain) can increase the availability of phosphorus to plant by mineralizing organic phosphorus compound and by converting inorganic phosphorus into more available form (MARSCHNER 1995, BARYOSEF et al 1999. Numerous studies have shown a fall in pH by production of organic acids when PBS strains are grown in liquid cultures (ASEA et al 1988, RODRIGUEZ andFRAGA 1999).…”