RÉSUMÉ
Soil salinization is a significant abiotic factor threatening agricultural production, while the low availability of phosphorus (P) in plants is another worldwide limitation. Approximately 95-99% of the P in soil is unavailable to plants. Phosphate-solubilizing bacteria (PSB) transform insoluble phosphates into soluble forms that plants can utilize. The application of PSB can replace or partially reduce the use of P fertilizers. Therefore, selecting bacteria with high solubilization capacity from extreme environments, such as saline soils, becomes crucial. This study aimed to identify twenty-nine bacterial strains from the rhizosphere of Salicornia fruticosa by sequencing the 16S rDNA gene, evaluate their development in increasing concentrations of NaCl, classify them according to their salinity response, and determine their P solubilization capability. The bacteria were cultivated in nutrient agar medium with NaCl concentrations ranging from 0.5% to 30%. The phosphate solubilization capacity of the bacteria was evaluated in angar and broth National Botanical Research Institute (NBRIP) media supplemented with calcium phosphate (CaHPO4) and aluminum phosphate (AlPO4), and increased with 3% NaCl. All bacterial strains were classified as halotolerant and identified to the genera Bacillus, Enterobacter, Halomonas, Kushneria, Oceanobacillus, Pantoea, Pseudomonas, and Staphylococcus, with only one isolate was not identified. The isolates with the highest ability to solubilize phosphorus from CaHPO4 in the liquid medium were Kushneria sp. (SS102) and Enterobacter sp. (SS186), with 989.53 and 956.37 mg·Kg-1 P content and final pH of 4.1 and 3.9, respectively. For the solubilization of AlPO4, the most effective isolates were Bacillus sp. (SS89) and Oceanobacillus sp. (SS94), which raised soluble P by 61.10 and 45.82 mg·Kg-1 and final pH of 2.9 and 3.6, respectively. These bacteria demonstrated promising results in in vitro P solubilization and can present potential for the development of bioinput. Further analyses, involving different phosphate sources and the composition of produced organic acids, will be conducted to contribute to a comprehensive understanding of their applications in sustainable agriculture.
RÉSUMÉ
AIMS: To evaluate the colonization process of sugarcane plantlets and hydroponically grown rice seedlings by Gluconacetobacter diazotrophicus strain PAL5 marked with the gusA and gfp reporter genes. METHODS AND RESULTS: Sugarcane plantlets inoculated in vitro with PAL5 carrying the gfp::gusA plasmid pHRGFPGUS did not present green fluorescence, but beta-glucuronidase (GUS)-stained bacteria could be observed inside sugarcane roots. To complement this existing inoculation methodology for micropropagated sugarcane with a more rapid colonization assay, we employed hydroponically grown gnotobiotic rice seedlings to study PAL5-plant interaction. PAL5 could be isolated from the root surface (10(8) CFU g(-1)) and from surface-disinfected root and stem tissues (10(4) CFU g(-1)) of inoculated plants, suggesting that PAL5 colonized the internal plant tissues. Light microscopy confirmed the presence of bacteria inside the root tissue. After inoculation of rice plantlets with PAL5 marked with the gfp plasmid pHRGFPTC, bright green fluorescent bacteria could be seen colonizing the rice root surface, mainly at the sites of lateral root emergence, at root caps and on root hairs. CONCLUSION: The plasmids pHRGFPGUS and pHRGFPTC are valid tools to mark PAL5 and monitor the colonization of micropropagated sugarcane and hydroponic rice seedlings. SIGNIFICANCE AND IMPACT OF THE STUDY: These tools are of use to: (i) study PAL5 mutants affected in bacteria-plant interactions, (ii) monitor plant colonization in real time and (iii) distinguish PAL5 from other bacteria during the study of mixed inoculants.
