Aroma profile of Oenococcus oeni strains in different life styles

Abstract

AIM: Three Oenococcus oeni strains previously isolated from spontaneous malolactic fermentation were characterized for their surface properties. Planktonic and sessile cells were investigated for aroma compounds production and the expression of genes involved in citrate and malate metabolism (citE and mleA, respectively), glycoside-hydrolase (dsrO), fructansucrase (levO), rhamnosyl-transferase (wobB), glycosyltransferase (wobO).

METHODS: Bacterial adhesion on polystyrene was evaluated using 96-well plates in MRS and must. Planktonic and sessile cells were numbered by plate count. Biofilm formation was also visualized by confocal laser scanning microscopy (CLSM, Nikon A1R) using hoechst fluorescent dye. Aroma compounds produced by sessile and planktonic cells were determined by solid phase microextraction coupled with gas chromatography (GC/MS SPME). RNA was extracted using using the Tri-reagent method (Sigma-Aldrich) according to the manufacturer’s instructions. Real-time analysis was performed using an iCycler IQ realtime PCR Detection System (Bio-Rad). ldhD and gyrA were used as reference genes. Fold changes were determined using the 2-ΔΔCT method.

RESULTS: The strains adhered to polystyrene in presence of MRS and must. In any case all strains preferred the planktonic state. CSLM was used to visualize cells distribution and their aggregation and confirmed that strains were able to form biofilm in must and MRS in a strain specific way. Quantitative and qualitative differences on aromatic compounds production were also detected. Higher alcohols and esters were mainly produced in the planktonic state, while organic acids in the sessile one. A strain specific behaviour was observed also for gene expression.

CONCLUSIONS: Biofilm formation can modulate aroma compounds production and probably the organoleptic characteristics of wine. Gene expression analysis revealed that aggregation state can influence malate and citrate metabolism. Further investigations are necessary to evaluate the interaction between Saccharomyces cerevisiae/non-Saccharomyces strains and O. oeni in biofilm formation in order to modulate wine characteristics.