Metagenome and volatilome unveil the functional potential of Mediterranean table olive microbiome

Background. The microbiota of table olives is usually dominated by lactic acid bacteria (mostly Lactiplantibacillus spp.) and yeasts (e.g., Saccharomyces cerevisiae, Candida boidinii, Wickerhamomyces anomalus). While several studies characterized its taxonomic composition, the functional potential is still unexplored. Moreover, the impact of microbiome dynamics on the volatilome also deserves further investigation. Methods. A total of 270 samples from different Mediterranean countries (Italy, Spain and Greece) were collected. Shotgun metagenomics was carried out by Illumina sequencing. Volatilome was analysed through Solid Phase Micro-Extraction (SPME) and Gas Chromatography Mass Spectrometry (GC-MS) analysis. Results. Lactiplantibacillus pentosus was the most abundant taxon in both natural and alkali-treated olives, while Saccharomyces cerevisiae was significantly lower in Spanish-style olives. The length of fermentation strongly influenced the community assembly by increasing the diversity of Lactic Acid Bacteria and reducing the presence of potentially spoilage microbes, which in turn reflected on the metabolic potential of the communities. In addition, strain-level analyses of LAB species identified markers of specific olive cultivar and processes. Natural and alkali-treated green olives showed higher ketone levels, while acids, esters, and alcohols were present at concentrations similar to those in Spanish-style olives. However, fermentation time significantly influenced the concentration of these volatile compounds, as observed in black natural olive samples. Conclusions. These findings advance our understanding of microbial markers and the volatilome in table olive production and may assist stakeholders in developing high-quality products. Acknowledgements This work was funded by the project METAOLIVE: meta-omic approaches for traditional table olive fermentation, funded by the European Union - NextGenerationEU, NRRP Missione 4 “Istruzione e Ricerca” - Componente C2, Investimento 1.1, “Fondo per il Programma Nazionale di Ricerca e Progetti di Rilevante Interesse Nazionale (PRIN)” (2022NN28ZZ).