Abstract
The growing interest in a healthy lifestyle and in environmental protection is changing habits regarding food consumption and agricultural practices. Good agricultural practice is indispensable, particularly for raw vegetables, and can include the use of plant probiotic bacteria for the purpose of biofertilization. In this work we analysed the probiotic potential of the rhizobial strain PEPV40, identified as Rhizobium laguerreae through the analysis of the recA and atpD genes, on the growth of spinach plants. This strain presents several in vitro plant growth promotion mechanisms, such as phosphate solubilisation and the production of indole acetic acid and siderophores. The strain PEPV40 produces cellulose and forms biofilms on abiotic surfaces. GFP labelling of this strain showed that PEPV40 colonizes the roots of spinach plants, forming microcolonies typical of biofilm initiation. Inoculation with this strain significantly increases several vegetative parameters such as leaf number, size and weight, as well as chlorophyll and nitrogen contents. Therefore, our findings indicate, for the first time, that Rhizobium laguerreae is an excellent plant probiotic, which increases the yield and quality of spinach, a vegetable that is increasingly being consumed raw worldwide.
Highlights
The consumption of salads, those sold as ready-to-eat that include the leaves of different vegetables, is increasing worldwide[1], but so too is the number of outbreaks of bacterial foodborne illnesses caused by eating raw leaves[2,3]
The analysis of the concatenated recA and atpD genes showed that PEPV40 was closely related to strains isolated in several continents, such as PEVF08, isolated from Vicia faba in Peru, BIHB 1107 isolated from Pisum sativum nodules in India, and Rrb[124] isolated in Poland (Fig. 1)
The strain PEPV40 produced 56.1 mg l−1 of indole acetic acid when grown in JMM liquid medium supplemented with tryptophan; the concentration of IAA was lower (0.14 mg l−1) when measured by HPLC
Summary
The consumption of salads, those sold as ready-to-eat that include the leaves of different vegetables, is increasing worldwide[1], but so too is the number of outbreaks of bacterial foodborne illnesses caused by eating raw leaves[2,3]. In addition to symbiotic nitrogen fixation, rhizobia have other PGP mechanisms, such as phosphate solubilisation and the production of siderophores and the phytohormone indole acetic acid (IAA)[9,13,15,16,17,18,19,20,21,22] This suggests that these bacteria can be used as a plant probiotic for non-legumes, a situation that has recently been reported for some cereals, fruits, and vegetables[9,13,15,16,19,20,21,23,24,25,26]. The aim of this study was to analyse the interaction between Rhizobium laguerreae and spinach plants, starting from the first steps of root colonization through to the final yield of leaves at different stages of growth
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