We characterized the Dekkera/Brettanomyces yeasts, which in nature often occupy a similar niche to Saccharomyces/Kluyveromyces yeasts. In fermentor experiments D. bruxellensis produced substantial amounts of ethanol under aerobic conditions and could also grow anaerobically, just like S. cerevisiae and its close relatives. In other words, D. bruxellensis can be classified as a Crabtree-positive and facultative anaerobic yeast. B. naardenensis, on the other hand, behaved more similarly to Kluyveromyces lactis, which is a Crabtree negative and aerobic yeast. Our phylogenetic analysis suggested that the Saccharomyces/Kluyveromyces and Dekkera/Brettanomyces groups separated at least 200 mya. In other words, the divergence took place long before the whole genome duplication (WGD), promoter rewiring, URA1 horizontal transfer and ADH duplication events that occurred in the S. cerevisiae lineage and are thought to be involved in the “make-accumulate-consume” strategy. When we analysed promoters belonging to rapid growth- and respiration- associated genes of S. cerevisiae and D. bruxellensis the AATTTT motif was present at the conserved position in rapid growth- but missing in the respiration-associated genes. While all other examined pre-WGD yeasts keep the motif at a fixed position in both the rapid growth and respiration associated gene sets, it appears that D. bruxellensis has, in parallel with the post-WGD lineage, undergone a large scale motif loss. In conclusion, apparently both lineages, post-WGD and D. bruxellensis, used the same molecular tool, global promoter rewiring, to change the regulation pattern of expression of respiration-associated genes resulting in ethanol accumulation and consequently in the development of the “make-accumulate-consume” strategy.
COBISS.SI-ID: 1953275
Industrial fermentation of lignocellulosic hydrolysates to ethanol requires microorganisms able to utilise a broad range of carbon sources and generate ethanol at high yield and productivity. In this work Brettanomyces/Dekkera yeasts were studied to explore their potential to produce ethanol from renewable sources under conditions suitable for industrial processes, such as oxygen-limited and low-pH conditions. Over 50 strains were analysed for their ability to utilise a variety of carbon sources. Two strains of D. bruxellensis were able to produce ethanol at high yield (0.44 g g−1 glucose), comparable to those reported for S. cerevisiae. B. naardenensis was shown to be able to produce ethanol from xylose. To obtain ethanol from synthetic lignocellulosic hydrolysates we developed a two-step fermentation strategy: the first step under aerobic conditions for fast production of biomass from mixtures of hexoses and pentoses, followed by a second step under oxygen limitation to promote ethanol production. Under these conditions we obtained biomass and ethanol production on synthetic lignocellulosic hydrolysates, with ethanol yields ranging from 0.2 to 0.3 g g−1 sugar. Hexoses, xylose and arabinose were consumed at the end of the process, resulting in 13 g l−1 of ethanol. Our studies showed that Brettanomyces/Dekkera yeasts have clear potential for further development for industrial processes aimed at production of ethanol from renewable sources.
COBISS.SI-ID: 1633787