Meyerozyma caribbica Isolated from Vinasse-Irrigated Sugarcane Plantation Soil: A Promising Yeast for Ethanol and Xylitol Production in Biorefineries.

The production of fuels and other industrial products from renewable sources has intensified the search for new substrates or for the expansion of the use of substrates already in use, as well as the search for microorganisms with different metabolic capacities. In the present work, we isolated and tested a yeast from the soil of sugarcane irrigated with vinasse, that is, with high mineral content and acidic pH. The strain of Meyerozyma caribbica URM 8365 was able to ferment glucose, but the use of xylose occurred when some oxygenation was provided. However, some fermentation of xylose to ethanol in oxygen limitation also occurs if glucose was present. This strain was able to produce ethanol from molasses substrate with 76% efficiency, showing its tolerance to possible inhibitors. High ethanol production efficiencies were also observed in acidic hydrolysates of each bagasse, sorghum, and cactus pear biomass. Mixtures of these substrates were tested and the best composition was found for the use of excess plant biomass in supplementation of primary substrates. It was also possible to verify the production of xylitol from xylose when the acetic acid concentration is reduced. Finally, the proposed metabolic model allowed calculating how much of the xylose carbon can be directed to the production of ethanol and/or xylitol in the presence of glucose. With this, it is possible to design an industrial plant that combines the production of ethanol and/or xylitol using combinations of primary substrates with hydrolysates of their biomass.

[Non-conventional yeasts as tools for innovation and differentiation in brewing]. / Levaduras no convencionales como herramientas de innovación y diferenciación en la producción de cerveza.

Yeasts play a crucial role in brewing. During fermentation, besides ethanol and carbon dioxide, yeasts produce a considerable number of organic compounds, which are essential for beer flavor. In particular, Saccharomyces cerevisiae and Saccharomyces pastorianus are traditionally used in the production of ale and lager beers, respectively. Nowadays, the continuous growth of the craft beer market motivates the production of differential and innovative beers; leading specialists and brewers focus on non-conventional yeasts as tools for new product development. In this work, we describe the potential application of non-conventional yeast species such as those of the genera Brettanomyces, Torulaspora, Lachancea, Wickerhamomyces, Pichia and Mrakia in the craft brewing industry, as well as non-traditional brewing yeasts of the Saccharomyces genus. Furthermore, the fermentation conditions of these non-conventional yeasts are discussed, along with their abilities to assimilate and metabolize diverse wort components providing differential characteristics to the final product. In summary, we present a comprehensive review of the state-of-the-art of non-conventional yeasts, which is highly relevant for their application in the production of novel craft beers including flavored beers, non-alcoholic beers, low-calorie beers and functional beers.

The biotechnological potential of the yeast Dekkera bruxellensis.

Dekkera bruxellensis is an industrial yeast mainly regarded as a contaminant species in fermentation processes. In winemaking, it is associated with off-flavours that cause wine spoilage, while in bioethanol production this yeast is linked to a reduction of industrial productivity by competing with Saccharomyces cerevisiae for the substrate. In spite of that, this point of view is gradually changing, mostly because D. bruxellensis is also able to produce important metabolites, such as ethanol, acetate, fusel alcohols, esters and others. This dual role is likely due to the fact that this yeast presents a set of metabolic traits that might be either industrially attractive or detrimental, depending on how they are faced and explored. Therefore, a proper industrial application for D. bruxellensis depends on the correct assembly of its central metabolic puzzle. In this sense, researchers have addressed issues regarding the physiological and genetic aspects of D. bruxellensis, which have brought to light much of our current knowledge on this yeast. In this review, we shall outline what is presently understood about the main metabolic features of D. bruxellensis and how they might be managed to improve its current or future industrial applications (except for winemaking, in which it is solely regarded as a contaminant). Moreover, we will discuss the advantages and challenges that must be overcome in order to take advantage of the full biotechnological potential of this yeast.

Effect of contamination with Lactobacillus fermentum I2 on ethanol production by Spathaspora passalidarum.

Second-generation bioethanol is a promising source of renewable energy. In Brazilian mills, the production of ethanol from sugarcane (first generation, 1G) is a consolidated process performed by Saccharomyces cerevisiae and characterized by high substrate concentrations, high cell density, and cell recycle. The main bacterial contaminants in 1G fermentation tanks are lactic acid bacteria, especially bacteria from the Lactobacillus genus, which is associated with a decrease in ethanol yield and yeast cell viability, among other negative effects. Second-generation (2G) bioethanol production is characterized by the conversion of glucose and xylose into ethanol by genetically modified or non-Saccharomyces yeasts. Spathaspora passalidarum is a promising non-Saccharomyces yeast for 2G ethanol production due to its ability to effectively convert xylose into ethanol. The effect of bacterial contamination on the fermentation of this yeast is unknown; therefore, L. fermentum, a common bacterium found in Brazilian 1G processes, was studied in coculture with S. passalidarum in a fed-batch fermentation process similar to that used in 1G mills. Individually, L. fermentum I2 was able to simultaneously consume glucose and xylose in nutrient-rich broth (Man, Rogosa, and Sharpe (MRS + xylose) but failed to grow in a glucose- and xylose-based synthetic broth. In coculture with S. passalidarum, the bacteria remained at a concentration of 108 UFC/mL throughout cell recycling, but no flocculation was observed, and it did not affect the fermentative parameters or the cellular viability of the yeast. Under both conditions, the maximum ethanol production was 21 g L-1 with volumetric productivity ranging from 0.65 to 0.70 g L-1 h-1. S. passalidarum was thus shown to be resistant to L. fermentum I2 under the conditions studied.