Mixed culture fermentation using Torulaspora delbrueckii and Saccharomyces cerevisiae with direct and indirect contact: impact of anaerobic growth factors

Abstract

The role of the initial concentration of anaerobic growth factors (AGF) on interactions between Torulaspora delbrueckii and Saccharomyces cerevisiae was investigated in strict anaerobiosis. Experiments were performed in a synthetic grape must medium in a membrane bioreactor, a special tool designed for studying direct and indirect interactions between microorganisms. In pure culture fermentations, increased AGF concentration had no impact on S. cerevisiae behaviour, whereas it induced an extension of T. delbrueckii latency. Surprisingly, T. delbrueckii used only 75 to 80% of the consumed sugar to produce biomass, glycerol and ethanol. Physical separation influenced the population dynamics of cofermentations. S.cerevisiae dominated the co-cultures having a single dose of AGF as its presence indirectly induced a decrease in numbers of living T. delbrueckii cells and physical contact with T. delbrueckii stimulated S.cerevisiae growth. Increasing the AGF initial concentration completely upset this domination: S. cerevisiae growth was not stimulated and T. delbrueckii living cells did not decrease. Yeasts incorporate exogenous AGFs, which probably impact their response to competing yeasts. The increase in AGF might have induced changes in the lipid composition of the T. delbrueckii membrane, which would hinder its interaction with S. cerevisiae antimicrobial peptides. The initial concentration of anaerobic growth factors influenced co-culture fermentation population dynamics tremendously, thus highlighting a new way to monitor population evolution and eventually wine organoleptic properties.

Impact of Nutrient Availability on the Fermentation and Production of Aroma Compounds Under Sequential Inoculation With M. pulcherrima and S. cerevisiae

“…After being considered spoilage yeasts for decades, the potential of non-Saccharomyces (NS) species to increase the aromatic complexity and improve the sensory properties of wines has been acknowledged, and some NS strains are already available in the market as active dried yeasts. NS strains have been successfully used to decrease the final content of ethanol in wines (Contreras et al, 2014;Varela et al, 2016;Brou et al, 2018) or for the diversification of the aromatic profile of the product, increasing both the formation of fermentative aromas and the release of varietal aromas due to their capacity to excrete hydrolytic enzymes (Egli et al, 2002;Rodríguez et al, 2010;Zott et al, 2011;Belda et al, 2017). Among these compounds, thiols play a central role, particularly in white wines, as they possess sought-after aromas of box tree, citrus and passion fruit.…”

Noninvasive tool for optical online monitoring of individual biomass concentrations in a defined coculture

“…In other studies, the population ratios and concentrations were determined offline by counting colony forming units on agar plates. This is either enabled by the use of selective antibiotics (Brou, Taillandier, Beaufort, & Brandam, 2018;Shimizu, Mizuguchi, Tanaka, & Shioya, 1999;Taniguchi et al, 1998) or the individual colonies were assigned to each species by different morphologies (Shekhawat, Bauer, & Setati, 2017). Another option is given by genetically introducing different fluorescence tags into each strain, allowing species-specific cell counting by flow cytometry (Spacova et al, 2018).…”

Measurement Techniques to Resolve and Control Population Dynamics of Mixed-Culture Processes

“…Furthermore, two still-dominant methods for the offline quantification of complex mixed-culture systems are plate counting and 16S rDNA sequencing [44][45][46][47][48]. Classical plate counting appears outdated due to a huge amount of manual work as well as an unintended preselection of microorganisms growing on solid media.…”