Unraveling the Microbiota of Natural Black cv. Kalamata Fermented Olives through 16S and ITS Metataxonomic Analysis

Abstract

Kalamata natural black olives are one of the most economically important Greek varieties. The microbial ecology of table olives is highly influenced by the co-existence of bacteria and yeasts/fungi, as well as the physicochemical parameters throughout the fermentation. Therefore, the aim of this study was the identification of bacterial and yeast/fungal microbiota of both olives and brines obtained from 29 cv. Kalamata olive samples industrially fermented in the two main producing geographical regions of Greece, namely Aitoloakarnania and Messinia/Lakonia. The potential microbial biogeography association between certain taxa and geographical area was also assessed. The dominant bacterial family identified in olive and brine samples from both regions was Lactobacillaceae, presenting, however, higher average abundances in the samples from Aitoloakarnania compared to Messinia/Lakonia. At the genus level, Lactobacillus, Celerinatantimonas, Propionibacterium and Pseudomonas were the most abundant. In addition, the yeasts/fungal communities were less diverse compared to those of bacteria, with Pichiaceae being the dominant family and Pichia, Ogataea, and Saccharomyces being the most abundant genera. To the best of our knowledge, this is the first report on the microbiota of both olives and brines of cv. Kalamata black olives fermented on an industrial scale between two geographical regions of Greece using metagenomics analysis.

Microbial Diversity of Fermented Greek Table Olives of Halkidiki and Konservolia Varieties from Different Regions as Revealed by Metagenomic Analysis

“…Similarly, yeast diversity on olive surfaces was determined by targeting the ITS region of the nuclear ribosomal DNA, a widely accepted standard procedure for yeast identification not only in fermented table olives [19,20] but also in other food fermentations [55]. According to the results, the yeast microbiota of olive samples of both cultivars was less diverse compared to bacteria, a finding in accordance with the results obtained previously regarding fermented natural black olives cv.…”

“…In a recent study, the presence of Lactobacillus was also highly influential for the differentiation of Greek-style fermented olives cv. Kalamata from different geographic regions [20]. Furthermore, the species Lactobacillus paracollinoides was identified as responsible for the discrimination of Spanish-style green olive fermentations among different patios [22].…”

“…According to the results, the yeast microbiota of olive samples of both cultivars was less diverse compared to bacteria, a finding in accordance with the results obtained previously regarding fermented natural black olives cv. Kalamata [20].…”

“…In addition, the variable importance on projection (VIP) was used to identify the most important variables. A VIP value of 1.0 has generally been accepted as a cut-off limit in variable selection; thus, variables exceeding this limit were considered to be highly influential [20]. Heatmaps were also performed for data visualization.…”

“…However, information about the microbial diversity of natural black and Spanish-style green olive fermentations for Greek table olive varieties is scarce. Recently, Kazou et al [20] performed 16S and internal transcribed spacer (ITS) metataxonomic analysis to unravel the microbiota of natural black cv. Kalamata fermented olives on both olives and brines.…”