Exploring the plant-growth promoting bacterium Herbaspirillum seropedicae as catalyst of microbiome remodeling and metabolic changes in wheat plants

Inoculation with the PGPB Herbaspirillum seropedicae shapes both the structure and putative functions of the wheat microbiome and causes changes in the levels of various plant metabolites described to be involved in plant growth and health. Plant growth promoting bacteria (PGPB) can establish metabolic imprints in their hosts, contributing to the improvement of plant health in different ways. However, while PGPB imprints on plant metabolism have been extensively characterized, much less is known regarding those affecting plant indigenous microbiomes, and hence it remains unknown whether both processes occur simultaneously. In this study, both 16S amplicon and ITS sequencing analyses were carried out to study both the structural as well as the putative functional changes in the seed-borne endophytic microbiome of wheat plants inoculated with the PGPB Herbaspirillum seropedicae strain RAM10. Concomitantly, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) analyses were used to investigate the alterations in the root metabolome of PGPB-inoculated plants. PGPB inoculation led to marked differences in the composition of the root microbiome, accompanied by the differential enrichment of microorganisms with putative roles in both plant energy and nitrogen metabolism. In addition, metabolome analyses showed that the levels of 16 metabolites belonging to the phenylpropanoid, terpenoid, and unsaturated fatty acid families were significantly altered in PGPB-inoculated plants. These findings shed light on the interplay between PGPB, the plant and its associated microbiome, indicating that PGPB can act as the driving force mediating long-lasting changes in both the plant metabolome and the plant microbiome.