Phytochemical profiling of tomato roots following treatments with different microbial inoculants as revealed by IT-TOF mass spectrometry

Background: In light of the growing interest for eco-compatible fertilization, tomato plant roots were treated with four different strains of microorganisms (B1–B4) capable of positively affecting plant growth. The methanolic extracts from treated roots were analysed by reverse phase ultra-high-performance liquid chromatography hyphenated with ion trap time-of-flight high-resolution mass spectrometry to compare their metabolites with that of control plants (B0). Results: We found, in both treated and control plants, several primary metabolites, such as fatty acids and coumaric acid, and other compounds associated with secondary metabolism pathways such as that of cyclopentaneoctanoic acid (CPOA) or hydroxyoctadecadienoic acid (HODE), and additional molecules which were not characterizable with the available data. A semiquantitative assessment of all metabolites became the basis for further processing the metabolic results by principal component analysis, which highlighted significant differences in the PC1 and PC2 components. The PC1 was particularly affected by the presence of arachidonic acid, myristic acid, and two unidentified metabolites. It effectively differentiated control plants from all bioeffectors treatments, and, in particular, the B4 treatment from the rest (B1–B3). The PC2 was mainly affected by palmitic acid, heptadecanoic acid, two CPOAs, one HODE and two unidentified metabolites. These metabolites successfully differentiated the B0 control from all the bioeffectors treatments, and, especially, showed a difference between B1 and B2. Conclusions: Our findings suggest that changes in secondary pathways of lipid metabolism may underlie the biostimulation exerted by the four microbial bioeffectors of this study, and that LC–MS coupled by multivariate analysis can easily fingerprint the metabolic alterations induced by bioeffectors in tomato roots.