New insights into the long-term preservation of microbial communities associated with Apulian table olives

Microbial biodiversity associated with fermented foods is a crucial resource for promoting human health and boosting innovation in the food industry. Scientific research and biotechnological valorization of specific microbial consortia require the preservation of their viability and functionality, which are the traits guaranteed by Microbial Culture Collections. However, assessing the best practices to promote the maintenance and revitalization of complex microbial communities is still challenging. Here, we present the strategies designed for the long-term preservation of microbiomes associated with table olives, a relevant example of plant-based fermented food worldwide, a key product in the Mediterranean diet, and among the main heritage foods in the Apulian region. The fermentation of these matrices is driven by a complex community involving mainly lactic acid bacteria and yeasts. To assess the best condition for their preservation, naturally fermented olives cv. Leccino, a typical Apulian cultivar, were sampled. Two cryopreservation protocols were developed by using 15% glycerol or DMSO as cryoprotectants and a storage temperature of -135 °C. The microbial consortium was studied before and during a 1-year storage period using a culture-dependent approach, RNA-based metabarcoding analysis, and metabolic profiling evaluation by Biolog Ecoplate®. The results showed that after 1 year of cryopreservation, the viability of the microbial consortium slightly decreased, regardless of the cryoprotectant used, and no significant changes in the metabolic profile were observed. Moreover, the metabarcoding analysis showed no significant differences in relative abundances after the storage period. Thus, we confirmed the effectiveness of the developed cryopreservation protocols, proper preservation of the microbial consortium, and its functionality during a long-term storage period.