Rhizobium sp. as a Growth Inducer of Phaseolus vulgaris L., Determining the Qualitative Chemical Composition of Its Ethyl Acetate Extract Using High-Resolution Liquid Chromatography Coupled with Mass Spectrometry

Phaseolus vulgaris L. is one of the most important legumes for human consumption due to its contents of proteins, antioxidants, minerals, and bioactive compounds. In the last decade, there has been a growing research interest in increasing yields while reducing or replacing the use of chemical fertilizers. This has led to a focus on plant growth-promoting Rhizobacteria (PGPR) as biofertilizers in sustainable agricultural practices. The aim of this study was to determine the growth-promoting activity of a culture broth of the Gram-negative soil bacteria Rhizobium sp. (F7), which is conserved in the Collection of Beneficial Bacteria at the Institute of Fundamental Research in Tropical Agriculture (INIFAT), and to identify the main secondary metabolites present in the ethyl acetate crude extract using high-resolution liquid chromatography coupled with mass spectrometry (UHPLC-ESI-MS/MS). The growth-promoting activity of the culture broth on Phaseolus vulgaris L. seeds was evaluated. The ethyl acetate extract was obtained by liquid–liquid extraction with ethyl acetate from the culture broth, and UHPLC-ESI-MS/MS was used to identify secondary metabolites. The results indicated that the culture broth of Rhizobium sp. exhibited an in vitro growth-stimulating effect. Furthermore, ten secondary metabolites were identified in the ethyl acetate extract (p-coumaric acid, indole-3-lactic acid, naringenin, and siderophores B and C, among others). These findings highlight the bioactive metabolites produced by Rhizobium sp., a bacterial strain of the INIFAT collection, which have a positive effect as growth promoters in plants. They reveal the potential of Rhizobium sp. as a promising candidate for inclusion in agricultural management practices.