Metabolismo de monossacarídeos de biomassa algal por linhagens de leveduras isoladas de alga verde

Abstract

Brazil is the world's second largest producer of fuel ethanol, with an annual volume of approximately 30 billion liters. This expressive production volume is mainly due to the alcoholic fermentation of sugarcane juice and/or molasses, a process that is already fully established, consecrated and optimized, called first-generation ethanol (1G). In the search for new alternatives for ethanol production, aiming to guarantee an alternative to food crops and reduce the water footprint, the second- and third-generation fuel processes are under development. The 2G-ethanol production occurs from residual plant biomass and has been widely studied. 3G ethanol, which comes from algae biomass, needs to be studied mainly in the fermentation stage, given the variability of carbohydrates present in algae hydrolysates and the absence of microorganisms able to metabolize them. Thus, firstly, the present study aimed to analyze five yeast strains isolated from decaying green algae in culture media containing the main monosaccharides found on algal biomass hydrolysates: glucose, mannose, xylose and galactose. Subsequently, following a Placket & Burman (P&B) experimental design, these five wild yeast strains and two Saccharomyces cerevisiae industrial strains were subjected to sugar-mixed cultures in order to analyze the influence of multiple variables (pH, temperature, NaCl concentration and concentration of the reducing sugars glucose, mannose, xylose, galactose and rhamnose) on the fermentation process. All wild yeast strains were able to metabolize the analyzed sugars separately, consuming them partially or totally after 24 h of incubation. Ethanol production was also verified for all strains grown in glucose and mannose, with emphasis on the 3.7 g.L-1 produced by CHAP-130 from mannose, and 0.65 g.L-1 from galactose. In the P&B experimental design, which contained different proportions of sugar mix, the superior performance of the wild strains CHAP-154 and CHAP-155 in relation to the industrial strains under the condition of the central points stands out, with a production of 3.2 and 4.4 g.L-1 of ethanol and consumption of 33 and 40% of total reducing sugars, respectively. In addition, isolated macroalgae yeasts also demonstrated tolerance to NaCl and high temperatures. Thus, the data obtained suggest that the analyzed strains may contribute to the optimization of third-generation ethanol production.