Metabolomic analysis of Trichoderma spent media
To evaluate if the overall differences in rhizobial strains response toTrichoderma 1W spent media could be related to the presence of species-specific differences in metabolite composition, a gas chromatography-mass spectrometry (GC-MS) analysis of theTrichoderma spp. 1W spent media was performed. The GC-MS profiling detected a total of 987 peaks (Supplementary Dataset S1 ), 76 of which could be identified (cut-off >80% of identification probability). These mainly belong to aromatic, cyclic and aliphatic hydrocarbons, carboxylic acids, alcohols, esters, sugars and their derivatives, terpenes and their derivatives.
Spent media were mainly composed by 2H-Pyran-2-one, 6-pentyl- (a representative metabolite common to the Trichoderma genus), 1-Monopalmitin, a compound known for having activity against pathogenic organisms , and succinic acid, monoethyl ester. The peak area of these and of the other compounds varied among samples (seeSupplementary Dataset S1, worksheet 2 ). Principal component analysis (PCA) (Figure 2 ) indicated strong differences inT. gamsii and T. harzianum spent media, while T. tomentosum and T. velutinum were more similar. The biplot analysis showed that differences in 2H-Pyran-2-one, 6-pentyl- quantities were associated with T. gamsii vs. the other fungi. T. tomentosum profiles were related to differences in 1-Monopalmitin. Other compounds contributing to the main differences were Hexadecane and Octadecanoic acid, 2,3-bis[(trimethylsilyl)oxy]propyl ester.T. velutinum spent medium profiles were associated with differences for 1-Monopalmitin, and succinic acid, monoethyl ester. The compound 2,3,4,5,6-Pentahydroxyhexanal was associated with T. harzianum spent medium. It is worth noting that the difference betweenT. gamsii and T. tomentosum/T. velutinum highlighted in the biplot is in good agreement with the phenotypic differences observed in the overall panel of rhizobial strain (Figure 1 ), suggesting that possibly some of the compounds mentioned above may target rhizobial metabolism, giving rise to contrasting bacterial responses.