Evaluating the effect of environmental parameters on the dynamics of the wine yeast consortium

Bagheri, Bahareh (2018-03)

Thesis (PhDAgric)--Stellenbosch University, 2018.

Thesis

ENGLISH ABSTRACT: Wine fermentation is a complex biochemical process which is characterized by the sequential development of various weakly and strongly fermentative yeast species. Thus, in such a multispecies consortium, individual species interact with one another and with their environment. Consequently, final chemical composition of wine will be affected significantly by the contribution of individual species as well as yeast-yeast interactions present in a wine consortium. The contribution of individual strain in the wine consortium is affected by several biotic (ecological interactions, killer factors, and grape variety) as well as abiotic parameters (temperature, sulphur dioxide, oxygen and nutrient availability). However, each strain will be affected differently by the combination of these parameters. Previous studies in wine fermentations have mainly focused on mixed culture fermentations composed of two species. Thus, fundamental rules underlying the effect of these parameters in a multi-species ecosystem are not fully understood. To decipher the principles that govern the complex wine ecosystem, a simplified model consortium comprising eight species commonly encountered in South African grape microbiota was established. An Automated ribosomal intergenic spacer analysis (ARISA) method was also developed in order to monitor population dynamics of the yeast consortium. The influence of presence of Saccharomyces cerevisiae as a biotic stress was investigated on the dynamics of yeast consortium in synthetic must using plating method and ARISA. Furthermore, the yeast consortium was used as an inoculum in Chenin blanc grape must where the population dynamics were monitored by plating method. The results confirmed that a selective pressure applied by the keystone species, S. cerevisiae modified the pattern of population dynamics. Wine ecosystem was characterized by supportive and inhibitory interactions. Furthermore, in spite of the differences between the two grape matrices, a similar pattern of population dynamics was observed in both fermentations. This observation suggested broad applicability of the model consortium to study the ecological interactions in the wine fermentation. In the next step, the variation in initial cell densities of each member of the consortium was used as a tool to untangle the contribution of individual strain in the population dynamics and wine aroma. The data suggest that S. cerevisiae applied a selective pressure to suppress the growth of main competitor in the wine ecosystem. Moreover, the presence of individual non-Saccharomyces species at a higher cell density, favoured the growth of some non-Saccharomyces species while suppressing the growth of others in the yeast consortium. Lastly, the effect of temperature and sulphur addition on the dynamics of the yeast consortium was evaluated in the synthetic must and real grape must fermentations. The results demonstrated that ecological interactions are largely independent of the matrix, confirming that the constructed multispecies consortium is a robust model that can be used as a tool to predict microbial behavior from a simple ecosystem to the complex natural environment. Furthermore, the effect of temperature and sulphur dioxide on the growth of non-Saccharomyces species was species/strain dependent. The results suggest that environmental parameters modify the pattern of population dynamics. However, ecological interactions seem to drive the wine ecosystem. The current study for the first time revealed the potential of a multi-species yeast consortium in understanding the ecological interactions in wine fermentation.

AFRIKAANSE OPSOMMING: Wynfermentasie is 'n komplekse biochemiese proses wat deur die opeenvolgende ontwikkeling van verskeie swak en sterk fermenterende gis spesies gekarakteriseer word. Dus, in so 'n multispesie konsortium, is daar 'n interaksie tussen die individuele spesies en tussen die spesies en hul omgewings. Gevolglik sal die finale chemise komposisie van die wyn beduidend deur die bydrae van individuele gis spesies en die gis-gis interaksies teenwoordig in die wyn beïnvloed word. Die bydrae van individuele gisrasse in die wynkonsortium word deur verskeie biotiese (ekologiese interaksies, “killer” faktore en druifvariëteit) sowel as abiotiese faktore (temperatuur, swaweldioksied, suurstof en die beskikbaarheid van voedingstowwe) beïnvloed. Elke gisras sal egter verskillend deur die kombinasie van die faktore beïnvloed word. Vorige studies wat handel oor wynfermentasie het hoofsaaklik op gemengde kultuur fermentasies met twee gis spesies gefokus. Dus is die onderliggende fundamentele reëls van die faktore in 'n multi-spesie ekosisteem nie volledig verstaan nie. Om die beginsels wat die komplekse wyn ekosisteem regeer te ontsyfer, is 'n vereenvoudigde model konsortium, bestaande uit agt spesis wat algemeen voorkom in Suid-Afrikaanse druifmikrobiota, gevestig. 'n Outomatiese ribosomale intergeniese spasiëringsanalise (ORISA) metode was ook ontwikkel om die bevolkings dinamika van die giskonsortium te monitor. Die invloed van die teenwoordigheid van Saccharomyces cerevisiae as 'n biotiese stres faktor op die dinamika van die giskonsortium in 'n sintetiese druiwemos was ondersoek deur die uitplaat metode en ORISA te gebruik. Die giskonsortium was verder gebruik as 'n inokulum in Cenin blanc druiwe mos waar die bevolkingsdinamika deur die uitplaat metode gemonitor was. Die resultate bevestig dat die geselekteerde druk wat deur die hoeksteen spesies, S. cerevisiae, uitgevoer was die patroon van die bevolkingsdinamika verander het. Die wynekosisteem was gekarakteriseer deur die ondersteunende en inhiberende interaksies. Ten spyte van die verskille tussen die twee druifmatrikse is 'n soortgelyke patroon van bevolkingsdinamika in beide fermentasies waargeneem. Hierdie observasie stel die wye toepassing van die model konsortium om die ekologiese interaksies in wynfermentasie te bestudeer voor. In die volgende stap is die variasie in aanvanklike seldigthede van elke lid van die konsortium gebruik as 'n “tool” om die individuele bydrae van elke individuele gisras in die bevolkingsdinamika en wynaroma te bepaal. Die data stel voor dat S. cerevisiae 'n selektiewe druk toegepas het om die groei van die hoof kompeteerder in die wynekosisteem te onderdruk. Die teenwoordigheid van individuele nie-Saccharomyces spesies teen 'n hoër seldigtheid, het ook die groei van sommige nie-Saccharomyces spesies bevoordeel terwyl dit die groei van ander in die giskonsortium onderdruk het. Laastens is die effek van temperatuur en swawel toevoegings op die dinamika van die giskonsortium geëvalueer in die sintetiese druiwe mos en werklike druiwe mos fermentasies. Die resultate demonstreer dat ekologiese interaksies grootliks onafhanklik is van die matriks, wat bevestig dat die bewerkstelling van 'n multi-spesies konsortium 'n robuuste model is wat gebruik kan word as 'n tool om die mikrobiale gedrag van 'n eenvoudige ekosisteem tot 'n komplekse natuurlike omgewing kan voorspel. Daarbenewens is die effek van temperatuur en swaweldioksied op die groei van nie- Saccharomyces spesies afhanklik van die spesies/ras. Die resultate stel voor dat omgewings faktore die patroon van bevolkingsdinamika verander. Nietemin blyk dit dat die ekologiese interkasies die wynekosisteem dryf. Die huidige studie het vir die eerste keer die potensiaal van 'n multi-spesies giskonsortium onthul om die ekologiese interaksies in wynfermentasie te verstaan.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/103812
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