Gluconic acid production and phosphate solubilization by the plant growth-promoting bacterium Azospirillum spp.

Abstract

In vitro gluconic acid formation and phosphate solubilization from sparingly soluble phosphorus sources by two strains of the plant growth-promoting bacteria A. brasilense (Cd and 8-I) and one strain of A. lipoferum JA4 were studied. Strains of A. brasilense were capable of producing gluconic acid when grown in sparingly soluble calcium phosphate medium when their usual fructose carbon source is amended with glucose. At the same time, there is a reduction in pH of the medium and release of soluble phosphate. To a greater extent, gluconic acid production and pH reduction were observed for A. lipoferum JA4. For the three strains, clearing halos were detected on solid medium plates with calcium phosphate. This is the first report of in vitro gluconic acid production and direct phosphate solubilization by A. brasilense and the first report of P solubilization by A. lipoferum. This adds to the very broad spectrum of plant growth-promoting abilities of this genus.

Antifungal Activity and Genetic Diversity of Selected Endophytic Fluorescent Pseudomonads

“…On the other hand, the strain SAW23 was the lowest efficient strain in solubilizing of phosphate (12.57 mg P l -1 ). The decrease in pH values clearly indicates the production of organic acids, which is considered to be the mechanism responsible for P solubization (Rodriguez et al, 2004). Similar results were confirmed by previous works by (Kpomblekou and Tabatabai, 1994;Nautiyal et al, 2000).…”

Phosphate solubilization by Rhizobium strains

“…strain 26, maximum solubilization was observed at 1.5% glucose concentration and above this concentration TCP solubilization decreased. This could be due to the autoconsumption of soluble phosphate by the growing bacterial population as reported in Azospirillum brasilense [17]. The variation in the effect of different concentrations of glucose is found to be statistically signifi cant.…”

Agricultural uses of plant biostimulants

“…In contrast, gluconic acid seems to be the most frequent organic acid produced by bacteria such as Azospirillum spp. (Rodríguez et al 2004), Pseudomonas spp., Erwinia herbicola, Pseudomonas cepacia, and Burkholderia cepacia (Rodriguez and Fraga 1999). Organic phosphorus, which is about 30-80 % of soil phosphorus, plays an important role in the phosphorus cycle of agricultural soils (Tarafdar and Gharu 2006).…”