Mon projet postdoctoral s'inscrit dans une collaboration entre l'UMR SPO, l'IWBT de Stellenbosch (Afrique du Sud) et la société Lallemand. Responsables scientifiques : Prof. Benoit Divol (IWBT) et Carole Camarasa (UMR SPO).

Deux projets sont développés dans ce cadre:

• Project 1 : Uptake and utilisation of nutrients by non-conventional yeasts: an asset for diversifying and improving wine quality?

This project proposes to investigate the nitrogen requirements of selected non-Saccharomyces yeasts (several strains within specific species will be studied) at the level of mixed and individual nitrogenous compounds (ammonium and individual amino acids). The outcome of these compounds’ metabolism will also be studied, in an attempt to identify the origin of the different fermentative aromas produced (i.e. carbon, nitrogen and sulphur metabolism). Based on the results obtained, supplementation with specific nitrogen sources will be tested in order to optimise the growth and therefore the aromatic contribution) of non-Saccharomyces yeasts. The project will appeal to both global techniques as (i) the phenotypic screening to study inter- and intraspecific diversity of nitrogen metabolism of non-conventional yeasts and (ii) transcriptomic analysis to understand the regulation of nitrogen metabolism; but also cutting-edge techniques such as isotopic filiation to understand the fate of nitrogen sources. This information will also allow to enhance our fundamental knowledge on the nitrogen metabolism on non-conventional yeasts which so far remains poorly characterised. Furthermore, formulations of mixture of nitrogen compounds to promote the contribution of selected non-conventional yeasts could be proposed to the wine industry as well as new yeast strain for commercialisation. 

Project 2 : Requirement and assimilation of lipid sources by wine yeasts: an asset for improving their fermentation performances?

The project aims to investigate the lipid requirements of specific non-conventional yeasts selected as representative of South African microbial diversity. Indeed, lipids are essential nutrients for yeasts as they act as the main constituent of their membrane. The lipids play an important role by maintaining the fluidity of the membrane, thereby ensuring smooth and continuous fermentation. The ability of yeasts to assimilate the various lipids from grape juice during alcoholic fermentation will also be assessed because they are unable to synthesise their own lipids during this time. Based on the results obtained, the best strategy(ies) of nutrition to promote yeast growth and thus prolonging their persistence during the fermentation, and ultimately their contribution to sensory properties, will be tested.

Contact : Stéphanie Rollero (rollero@sun.ac.za)

Mes principales publications:

• Seguinot P, Rollero S, Sanchez I, Sablayrolles JM, Ortiz-Julien A, Camarasa C, Mouret JR. (2018). Impact of the timing and the nature of nitrogen additions on the production kinetics of fermentative aromas by Saccharomyces cerevisiae during winemaking fermentation in synthetic media. Food Microbiology 76: 29e39. doi.org/10.1016/j.fm.2018.04.005.
• Rollero, S., Roberts, S., Bauer, F.F., Divol, B. (2018). Agitation impacts fermentation performance as well as carbon and nitrogen metabolism in Saccharomyces cerevisiae under winemaking conditions. Aust. J. Grape Wine R. DOI:10.1111/ajgw.12338.
• Rollero, S., Bloem, A., Ortiz-Julien, A., Camarasa, C., Divol, B. (2018). Altered fermentation performances, growth and metabolic footprints reveal competition for nutrients between yeast species inoculated in synthetic grape juice-like medium. Front. Microbiol. doi: 10.3389/fmicb.2018.00196.
• Rollero S, Bloem A, Ortiz-Julien A, Camarasa C, Divol B. (2018). Fermentation performances and aroma production of non-conventional wine yeasts are influenced by nitrogen preferences. FEMS Yeast Res. doi: 10.1093/femsyr/foy055.
• Bloem, A., Rollero, S., Seguinot, P., Crépin, L., Perez, M., Picou, C., Camarasa, C. (2018). Workflow based on the combination of isotopic tracer experiments to investigate microbial metabolism of multiple nutrient sources. J. Vis. Exp. (131), e56393.
• Rollero, S., Mouret, J.R., Bloem, A., Sanchez, I., Ortiz-Julien, A., Sablayrolles, J.M., Dequin, S., Camarasa, C. (2017). Quantitative ¹³C-isotope labelling-based analysis to elucidate the influence of environmental parameters on the production of fermentative aromas during wine fermentation. Microbial Biotech. 10:1649-1662. IF:3.51
• Rollero, S., Mouret, J.R., Sanchez, I., Camarasa, C., Ortiz-Julien, A., Sablayrolles, J.M., Dequin, S. (2016). Key role of lipid management in nitrogen and aroma metabolism in an evolved wine yeast strain. Microb. Cell Fact. 15:32. IF:4.18
• Mouret, J.R., Cadiere, A., Aguera, E., Rollero, S., Ortiz-Julien, A., Sablayrolles, J.M., Dequin, S. (2015). Dynamics and quantitative analysis of the synthesis of fermentative aromas by an evolved wine strain of Saccharomyces cerevisiae. Yeast. 32, 257–269.
• Rollero, S., Bloem, A., Camarasa, C., Sanchez, I., Ortiz-Julien, A., Sablayrolles, J.M., Dequin, S., Mouret, J.R. (2015). Combined effects of nutrients and temperature on the production of fermentative aromas by Saccharomyces cerevisiae during wine fermentation. Appl. Microbiol. Biotechnol. 99, 2291–304.