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

Abstract

Seven phosphate-mobilizing pseudomonads were isolated, identified, and characterized in terms of their biofertilizer potential and root-colonizing properties. Pseudomonas protegens (ex-fluorescens) CHA0 was used for comparative purposes. Four isolates (LF-MB1, LF-P1, LF-P2, and LF-P3) clustered with members of the "Pseudomonas fluorescens complex," whereas the other three (LF-MB2, LF-V1, and LF-V2) clustered with members of the "Pseudomonas putida/Pseudomonas aeruginosa complex." Assays in buffered liquid growth medium supplemented with tricalcium phosphate enabled the separation of the isolates into two groups: group A (LF-P1, LF-P2, LF-P3, and LF-V1) solubilized P from 151 up to 182 μg mL −1 , and group B (LF-MB1, LF-MB2, and LF-V2) solubilized less than 150 μg PmL −1 . All isolates displayed acid and alkaline phosphatase activities. With the exception of LF-MB2, all isolates were able to degrade phospholipids from lecithin. Additionally, all isolates exhibited extracellular protease activity, and four isolates produced hydrogen cyanide, two traits that are related to biocontrol of phytopathogens. To study root colonization in non-sterile soil, isolates were doubly tagged with gfp and a tetracycline resistance cassette. After 15 days of competition with the indigenous bacterial flora, all tagged isolates colonized soybean roots at counts ranging from 7.6×10 5 to 1.7×10 7 CFU g −1 . The results indicate that there are already efficient phosphate-mobilizing pseudomonads adapted to agricultural bulk soils under no-till management in Argentina and thus having excellent potential for use as biofertilizers.

Rock-Phosphate Solubilising Bacteria and their Effect on Soybean (Glycine max) Growth under Pot Grown Conditions

“…and Bacillus sp. between solubilisation ability on plate and in liquid culture as mentioned in the previous investigations by Azziz et al [26] and Fernández et al [27]. Although all the strains showed good solubilisation in liquid cultures amended with the different rock phosphates, the amount of the solved P varied with the strain as well as the rock phosphate origin.…”

Isolation and Characterization of a Phosphorus-Solubilizing Bacterium from Rhizosphere Soils and Its Colonization of Chinese Cabbage (Brassica campestris ssp. chinensis)

“…Then, 20 μL was injected into the HPLC instrument (Essentia LC-15C, Japan), equipped with a C-18 column, and run at a flow rate of 1 mL/min using a 90:10 (v/v) methanol:phosphate buffer (10 mmol/L), pH 2.7, as the mobile phase; this process was monitored at 210 nm (Paavilainen and Korpela, 1993; Qin et al, 2010; Fernández et al, 2012). …”

Potential biocontrol actinobacteria: Rhizospheric isolates from the Argentine Pampas lowlands legumes

“…Proteolytic activities were detected as a clear zone around the colonies . The relative extracellular protease and phospholipase activities were calculated as (halo diameter/colony diameter) ×100 according to Fernández et al .…”

“…activities were calculated as (halo diameter/colony diameter) Â100 according to Fern andez et al [26]. Siderophore production was estimated on cromo azurol S (CAS) agar plates [27].…”