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.

Microbiology and Genetics Department University of Salamanca 37007 Salamanca Spain ICAAM Instituto de Ciências Agrárias e Ambientais Mediterrânicas Universidade de Évora Pólo da Mitra Ap 94 7002 554 Évora Portugal

Microbiology and Genetics Department University of Salamanca 37007 Salamanca Spain Institute of Microbiology ASCR v v i Vídeňská 1083 142 20 Prague Czech Republic

Microbiology and Genetics Department University of Salamanca 37007 Salamanca Spain Spanish Portuguese Institute for Agricultural Research Salamanca Spain

Microbiology and Genetics Department University of Salamanca 37007 Salamanca Spain Spanish Portuguese Institute for Agricultural Research Villamayor Salamanca Spain

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