Assessment of genetic and functional diversity of phosphate solubilizing fluorescent pseudomonads isolated from rhizospheric soil

Abstract

BackgroundPhosphorus is an essential macronutrient for the growth of plants. However, in most soils a large portion of phosphorus becomes insoluble and therefore, unavailable to plants. Knowledge on biodiversity of phosphate-solubilizing fluorescent pseudomonads is essential to understand their ecological role and their utilization in sustainable agriculture.ResultsOf 443 fluorescent pseudomonad strains tested, 80 strains (18%) showed positive for the solubilization of tri-calcium phosphate (Ca3(PO4)2) by the formation of visible dissolution halos on Pikovskaya's agar. These phosphate solubilizing strains showed high variability in utilizing various carbon sources. Numerical taxonomy of the phosphate solubilizing strains based on their carbon source utilization profiles resulted into three major phenons at a 0.76 similarity coefficient level. Genotypic analyses of strains by BOX (bacterial repetitive BOX element)-polymerase chain reaction (PCR) resulted into three distinct genomic clusters and 26 distinct BOX profiles at a 80% similarity level. On the basis of phenotypic characterization and 16S rRNA gene phylogenetic analyses strains were identified as Pseudomonas aeruginosa, P. mosselii, P. monteilii, P. plecoglossicida, P. putida, P. fulva and P. fluorescens. These phosphate solubilizing strains also showed the production of plant growth promoting enzymes, hormones and exhibited antagonism against phytopathogenic fungi that attack on various crops. Gene specific primers have identified the putative antibiotic producing strains. These putative strains were grown in fermentation media and production of antibiotics was confirmed by thin layer chromatography (TLC) and high performance liquid chromatography (HPLC).ConclusionPresent study revealed a high degree of functional and genetic diversity among the phosphate solubilizing fluorescent pseudomonad bacteria. Due to their innate potential of producing an array of plant growth promoting enzymes, hormones and antifungal metabolites these phosphate solubilizing strains are considered to play a vital role in plant growth promotion, disease suppression and subsequent enhancement of yield.

Plant-growth promoting effect of newly isolated rhizobacteria varies between two Arabidopsis ecotypes

“…In this experiment also P. fluorescens WCS417r was included, a strain that is known to induce systemic resistance in Arabidopsis, but does not promote growth. 37 Phosphate solubilization capacity of bacteria was detected according to (Naik 2008) 38 on agar plates…”

Pseudomonas spp. isolates with high phosphate-mobilizing potential and root colonization properties from agricultural bulk soils under no-till management

“…Among these, pseudomonad isolates are of interest because they usually exhibit additional plant probiotic traits such as antagonism to fungal pathogens and induced systemic resistance (Haas and Défago 2005;Picard and Bosco 2007;Barrett et al 2011), biodegradation of pollutants and of plant growth inhibitors (Ramette et al 2011), and biocontrol and biofertilization properties in agricultural fields (De Souza et al 2003). In addition, members of the genus Pseudomonas are excellent rhizosphere colonizers (Ravindra et al 2008;Browne et al 2009). These characteristics make pseudomonads interesting PGPR candidates as components of agricultural inputs to stimulate plant development and/or promote crop health.…”

“…Most agricultural soils contain large reserves of total P, commonly in the range of 200 to 5,000 mg Pkg −1 with an average of 600 mg Pkg −1 , due to the regular application of chemical fertilizers or sludge from wastewater treatment (Ravindra et al 2008). Both P fixation and precipitation occur in soil because of the large reactivity of phosphate ions with numerous soil constituents.…”

Klebsiella variicola and Klebsiella quasipneumoniae with capacity to adapt to clinical and plant settings

“…36 K. variicola and K. pneumoniae isolates were not able to solubilize phosphate (table II), which is a common characteristic among plant associated bacteria. Klebsiella genus, unlike other plant growth promoting bacteria, did not produce chitinases or proteases that may help fighting pathogenic fungi of plants (table II).…”