Isolation of pseudomonas strains with potential for protection of soybean plants against saline stress

Salinity is a major detrimental factor for plant growth and crop productivity that could be alleviated by the use of plant growth promoting bacteria (PGPB) with a protective role in such stressful conditions. In this study, four native strains of the genus Pseudomonas were isolated from both a strongly saline soil and the rhizosphere of soybean plants grown in a slightly saline soil. These isolates were able to tolerate high NaCl concentration, showed efficient adhesion to biotic and abiotic surfaces and efficiently colonized the rhizosphere of soybean grown in slightly saline soil. In these conditions, the four strains outperformed Pseudomonas putida KT2440, a strain known as a good root colonizer of different plants. Inoculation with all the isolates improved seed germination and vigor index, particularly in saline conditions, and one of them also had a positive effect on shoot length and phenological state of soybean plants grown in slightly saline soil. Our results suggest that the search for classical plant growth promotion traits may not be mandatory for selecting putative PGPB. Instead, characteristics such as stress tolerance, adhesion, competitive colonization, and plant growth promotion should be tested using the soil types and crops in which the bacteria will be used.This research was funded by Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) grant number PICT 2017-2285 and PICT 2018-3552, Fondo para la Investigación Científica y Tecnológica (FONCyT) grant number PIP 908-15, and Grant PID2019-109372GB-I00 (MCIN/AEI/10.13039/501100011033)

Pseudomonas stutzeri MJL19, a rhizosphere-colonizing bacterium that promotes plant growth under saline stress

Aims: The aim of this study was to find and use rhizobacteria able to confer plants advantages to deal with saline conditions. Methods and Results: We isolated 24 different bacterial species from the rhizosphere of halophyte plants growing in Santiago del Estero, Argentina salt flat. Four strains were selected upon their ability to grow in salinity and their biochemical traits associated with plant growth promotion. Next, we tested the adhesion on soybean seeds surface and root colonization with the four selected isolates. Isolate 19 stood out from the rest and was selected for further experiments. This strain showed positive chemotaxis towards soybean root exudates and a remarkable ability to form biofilm both in vitro conditions and on soybean roots. Interestingly, this trait was enhanced in high saline conditions, indicating the extremely adapted nature of the bacterium to high salinity. In addition, this strain positively impacted on seed germination, plant growth and general plant health status also under saline stress. Conclusions: A bacterium isolate with outstanding ability to promote seed germination and plant growth under saline conditions was found. Significance and Impact of the Study: The experimental approach allowed us to find a suitable bacterial candidate for a biofertilizer intended to alleviate saline stress on crops. This would allow the use of soil now considered inadequate for agriculture and thus prevent further advancement of agriculture frontiers into areas of environmental value.This work was funded by grants PIP 908/15 from CONICET, PICTs 2222/2014, 2285/2017 and 3552/2018 from FONCyT, and MHE-200019 from the EMHE-CSIC Progra

Plant growth promotion by Pseudomonas putida KT2440 under saline stress: role of eptA

New strategies to improve crop yield include the incorporation of plant growth-promoting bacteria in agricultural practices. The non-pathogenic bacterium Pseudomonas putida KT2440 is an excellent root colonizer of crops of agronomical importance and has been shown to activate the induced systemic resistance of plants in response to certain foliar pathogens. In this work, we have analyzed additional plant growth promotion features of this strain. We show it can tolerate high NaCl concentrations and determine how salinity influences traits such as the production of indole compounds, siderophore synthesis, and phosphate solubilization. Inoculation with P. putida KT2440 significantly improved seed germination and root and stem length of soybean and corn plants under saline conditions compared to uninoculated plants, whereas the effects were minor under non-saline conditions. Also, random transposon mutagenesis was used for preliminary identification of KT2440 genes involved in bacterial tolerance to saline stress. One of the obtained mutants was analyzed in detail. The disrupted gene encodes a predicted phosphoethanolamine-lipid A transferase (EptA), an enzyme described to be involved in the modification of lipid A during lipopolysaccharide (LPS) biosynthesis. This mutant showed changes in exopolysaccharide (EPS) production, low salinity tolerance, and reduced competitive fitness in the rhizosphere.This work was supported by the Agencia Nacional de Promoción Científica y Tecnológica (ANPCyT; grant PICT 2222) and Consejo de Investigaciones Científicas y Técnicas (CONICET; grant PIP 908/15) and partly supported by EMHE-CSIC (grant MHE200019) and Plan Estatal de I + D + I (MINECO and EFRD funds, grant BFU2016–80122-P)