Metabolomic and Transcriptional Profiling of Oleuropein Bioconversion into Hydroxytyrosol during Table Olive Fermentation by Lactiplantibacillus plantarum

Abstract

The study aims to elucidate the mechanisms responsible for the bioconversion of oleuropein into low molecular weight phenolic compounds in two selected L. plantarum strains, namely C11C8 and F3.5, under stress brine conditions and at two different temperatures (16°C and 30°C). For this purpose, we adopted an experimental strategy that combined high-resolution mass spectrometry, in silico functional analysis of glycosidic hydrolases GH1 encoding candidate genes and gene expression study. Oleuropein hydrolysis products and underlying enzymatic steps were identified, as well as a novel putative bgl gene, using seven strains belonging to the same species as controls, was detected. According to metabolomic analysis, a new intermediate compound (decarboxymethyl dialdehydic form of oleuropein aglycone) was revealed. In addition, the strain C11C8 showed a decrease in oleuropein content higher than F3.5 strain (30% vs 15%) at the temperature of 16°C. The highest increase in hydroxytyrosol was depicted by the strain C11C8 at the temperature of 30°C. PCR assay and sequencing analysis revealed that both strains possess bglH_1 , bglH_2 and bglH3 genes. Furthermore, RT-PCR assay showed that bglH_3 is the only gene transcribed in all tested conditions, while bglH_2 is switched off in strain C11C8 grown under cold temperature and no transcription was detected for gene bglH_1 . BglH_3 gene encodes a 6-phospho-beta-glucosidase, suggesting how phospho-β-glucosidase activity could belong to the overall metabolic strategy undertaken by L. plantarum to survive in an environment poor in free sugars, like table olive. Importance In the present study, a new candidate gene bglH_3 responsible for the β-glucosidase positive phenotype in L. plantarum was detected, providing the basis for future marker-assisted selection of L. plantarum starter strains with β-glucosidase positive phenotype. Furthermore, the ability of selected strains to hydrolyse oleuropein at low temperature is important for application as starter culture on an industrial-scale.

Transcriptional profiling of geniposide bioconversion into genipin during gardenia fructus extract fermentation by <i>Lactobacillus (Lactiplantibacillus) plantarum</i> SN13T

“…Most of these genes were accompanied by phosphotransferase system (PTS) EII components and transcriptional regulators in their gene operons. GH1 comprises enzymes with a number of known activities, including both β-glucosidase (EC 3.2.1.21) and 6-phospho-β-glucosidase (EC 3.2.1.86) [ 31 ]. In the published genome of L. plantarum WCFS1, 11 genes putatively encoding GH1 enzymes with phospho-β-glucosidase functionality were identified, nine of which were located adjacent to genes encoding β-glucoside/cellobiose-specific EII components.…”

“…These genes showed close resemblances to bglH2 and bglH3 genes encoding 6-phospho-β-glucosidases of L. plantarum ATCC 8014 arranged in a similar polycistronic bgl gene operon. Among them, bglH3 was reported to be a new candidate gene, and both genes were transcribed by L. plantarum C11C8, specifically during table olive fermentation, implying that phospho-β-glucosidase activity could be a metabolic strategy undertaken by L. plantarum to adapt in an environment poor in free sugars, as in the case of table olives [ 31 ].…”

The Rising Role of Omics and Meta-Omics in Table Olive Research

“…Kalogiouri et al [99] successfully discriminated PDO Greek Kalamata table olives from similarly processed olives from Egypt and Chile via ultra-high-performance liquid chromatography-quadrupole time-of-flight tandem mass spectrometry (UHPLC-ESI-QTOF-MS/MS), identifying 26 responsible compounds that could be used as markers for this discrimination. A metabolomic approach through ultra-high-performance liquid chromatography-high resolution mass spectrometry (UHPLC/HR-MS) was used by Vaccalluzzo et al [100] for the profiling of phenolic compounds during the fermentation of Nocellara Etnea table olives inoculated with two different Lactiplantibacillus strains (Lp. plantarum C11C8 and Lp.…”