Volatile organic compounds composition and dynamic during solid state fermentation

Streptomycetes are among the highest producers of a plethora of specialized metabolites. Among these,volatile organic compounds (VOCs) with antimicrobial activities give them an additional advantage as theymight inhibit competitors at a distance or indirectly triggering plant defense responses.Streptomyces sp. DEF603 is a strain isolated from Vitis vinifera that was characterized for its directantagonistic activity against phytopathogens. Phylogenetic analyses based on 16S rRNA gene, Multi-locusSequence Typing and whole genome demonstrated that DEF603 is closely related to Streptomycesalbidoflavus.This strain was grown on defatted wheat bran, a by-product of oil extraction from wheat and thevolatilome was analysed during solid-state fermentation to find active molecules against phytopathogens.Untargeted HS-SPME-GC-MS analysis was carried out at 4, 7, 10, and 14 days of fermentation to follow theshifts and changes in composition of volatile organic compounds. A total of 132 VOCs were putativelyidentified, primarily comprising terpenoids, alcohols, furans, aldehydes, ketones, and nitrogen-containingcompounds, among others. In the volatilome of Streptomyces-fermented substrate, common VOCs producedby streptomycetes such as geosmin and 2-methyl-pentanone, were found.Principal Component Analyses (PCAs) highlighted a clear separation (i) between inoculated and non-inoculated samples and (ii) among inoculated samples collected at different time points. The clustered heatmapanalysis, built on significant metabolites resulting from ANOVA, showed that the analysed volatilomes groupedin two main clusters, i.e. non-inoculated and inoculated substrates. Within the PLS-DA model, VariableImportance in Projection (VIP) statistics were used to pinpoint the metabolites responsible for the observedseparation. This analysis identified 21 potential volatile markers that significantly contributed to distinguishingdifferent groups. Interestingly, the amount of 12 compound increased during fermentation such as 2-pentanone, dimethyl trisulfide and 2-methyl-1-butanol that are reported as VOCs with antimicrobial activity.These results open the perspective to use raw material to produce VOCs with antimicrobial activity.