Phosphate-solubilization mechanism and in vitro plant growth promotion activity mediated by Pantoea eucalypti isolated from Lotus tenuis rhizosphere in the Salado River Basin (Argentina)

AIMS

To isolate and characterize phosphate-solubilizing strains from a constrained environment such as the Salado River Basin and to assess their phosphate-solubilizing mechanisms, to further selection of the most promising strains to inoculate and improve the implantation and persistence of Lotus tenuis in the most important area devoted to meat-cow production in Argentina.

METHODS AND RESULTS

Fifty isolates were obtained and through BOX-PCR analysis, 17 non-redundant strains were identified. Subsequently, they were found to be related to Pantoea, Erwinia, Pseudomonas, Rhizobium and Enterobacter genera, via 16S rRNA gene sequence analysis. This was in agreement with the clusters obtained by antibiotic resistance analysis. All isolates were tested for their phosphate-solubilizing activity and selected strains were inoculated onto L. tenuis plants. The most efficient isolate, was identified as Pantoea eucalypti, a novel species in terms of plant growth-promoting rhizobacteria.

CONCLUSIONS

The isolates obtained in this study showed a significant in vitro plant-growth promoting activity onto Lotus tenuis and the best of them solubilizes phosphate mainly via induction of the metabolism through secretion and oxidation of gluconic acid.

SIGNIFICANCE AND IMPACT OF THE STUDY

The use of these bacteria as bioinoculants, alone or in combination with nitrogen-fixing micro-organisms, could be a sustainable practice to facilitate the nutrient supply to Lotus tenuis plants and preventing negative side-effects such as eutrophication.

Cheese whey: an alternative growth and protective medium for Rhizobium loti cells

Cheese whey (CW)-based growth medium efficiently protects Rhizobium loti cells during freezing and desiccation and can maintain their growth in a manner similar to that of traditional mannitol-based medium (YEM). The cheese-whey-based medium (CW) improved viability when used to re-suspend cell pellets kept at -20 degrees C and -80 degrees C and resulted in the survival of over 90% of the cells. Moreover, bacterial pellets obtained from cells grown in CW withstand desiccation better than cells grown in YEM. Survival was over 60% after 30 days at 4 degrees C. No differences were observed in nodulation efficiency between YEM-grown and CW-grown cells. Fast protein liquid chromatography (FPLC) protocols are presented for total protein profile analyses of sweet and acid cheese whey.

Characterization of Rhizobium loti strains from the Salado River Basin

Thirty indigenous rhizobia strains, isolated from Lotus tenuis in the area of Chascomús and other regions of the Salado River Basin (Argentina), were characterized based on generation time, acid production, carbon utilization, protein profile, and molecular characterization by restriction fragment length polymorphism (RFLP) analysis of 16S rRNA genes amplified by the polymerase chain reaction (PCR). The results indicated that native rhizobia isolates from the Chascomús area are predominantly fast and intermediate-growers. The unclassified rhizobia examined by PCR-RFLP were found to be closely related to the reference strains of validly described Rhizobium species.

Isoxazolines and isoxazoles as factor Xa inhibitors

3,4,5-Trisubstituted isoxazolines (2) and isoxazoles (3) were prepared and evaluated for their in vitro and in vivo antithrombotic efficacy. They were compared to 3,5,5-trisubstituted isoxazolines (1) for Factor Xa selectivity and potency. They were also compared in an arterio-venous (A-V) shunt model of thrombosis.