Global and specific rhizobacteria-induced changes in the plant
shoot metabolome
LC-MS-based non-targeted metabolite profiling was used to investigate
the global and specific effects of each of the three rhizobacterial
strains on the occurrence and relative abundance of semi-polar secondary
metabolites in shoots of Arabidopsis, Artemisia and Broccoli. Emphasis
was given to metabolic alterations that differentiate effective from
ineffective plant-rhizobacteria partnerships. An overview of metabolites
that were significantly increased or reduced revealed that root
inoculation with Pbg exerted the largest alteration of the shoot
metabolomes of Artemisia and Arabidopsis, combinations that represent
the most effective and ineffective partnerships, respectively
(Supplementary Material, Figure S3 and Table
S3 ). Furthermore, most of the differential metabolites were unique for
plants inoculated with Pbg , i.e they were below the detection
limit in untreated control plants. In Broccoli, the ineffective
partnership with Pf SS101 accounted for the largest share of the
‘upregulated’ metabolites, whereas its effective partnership withPbg accounted for the largest share of ‘down-regulated’
metabolites (Supplementary Material, Figure S3 andTable S3 ). ANOVA with correction for multiple testing
(Benjamini and Hochberg), principal component analysis (PCA) and
hierarchical cluster analysis (HCA) were performed to investigate and
visualize metabolite clusters that were significantly altered (p
< 0.05, fold change > 2) in a rhizobacteria-plant
specific manner (Figure 2 ). Below, we will discuss the most
significant changes for each of the three plant species and the
interacting rhizobacterial strains.