Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) analysis of rhizobia nodulating Phaseolus vulgaris in different soils

Abstract

In this work, we analyzed by using MALDI-TOF MS (Matrix-Assisted Laser Desorption Ionization Time-of-Flight Mass Spectrometry) Phaseolus vulgaris nodulating strains isolated two different soils (soils 1 and 2) in León Province where this legume is commonly cultivated and it is protected by the GPI “La Bañeza”. These strains were compared with those isolated from P. vulgaris nodules in a third soil in the same zone identified as R. leguminosarum but belonging to different atpD and recA lineages that were added to the Rhizobiaceae database. The MALDI-TOF MS analysis showed that most of the strains isolated in soil 1 matched with the strain RPVR24 from the group II of R. leguminosarum, a strain isolated in a rainfed soil cultivated with P. vulgaris for 20 years in the same location (soil 3). However, almost all strains isolated from soil 2 matched with the strain RPVR32, also isolated in the soil 3, and belonged to a third phylogenetic group within R. leguminosarum. These results showed that MALDI-TOF MS is not only a reliable technique for identification at species level of fast-growing rhizobia, but also for differentiation of subspecific groups, which is very useful for ecological studies.