Lipid accumulation in wild Saccharomyces cerevisiae strains and their application for biodiesel

Conference poster, 2018

Our dependence on fossil fuels has severe consequences for both the environment and national economies worldwide. Considerable effort is being made in Europe and elsewhere to develop cheaper and cleaner energy sources. Biodiesel is one of the main alternatives, being renewable and environment-friendly, and with a wide acceptance in the European transport sector. However, its production is still mostly based on vegetable oils, leading to competition with the food industry and as a consequence to price increases of raw materials. Alternative feedstocks are required to ensure the sustainability of the biodiesel industry.

Oils produced by microorganisms are currently the most promising feedstock for sustainable biodiesel production. Yeast is attracting considerable attention, but the low productivity of these microorganisms on low or negative value substrates, such as lignocellulose-enriched residues, still hinders the industrial application of microbial oils. The development of robust yeast strains with increased oil yield and resistance to the different inhibitors present in the substrates is therefore one of the most important steps to improve the feasibility of microbial biodiesel [1].

Bioprospecting of wild environments frequently yields microorganisms with high resistance to a wide range of environmental stresses. Spontaneous fermentations of spirits are often associated with yeast strains adapted to high temperatures and capable of using multiple substrates [2]. In a previous study, yeast strains isolated from spontaneous cachaça fermentation vessels in Brazil exhibited lipid accumulation in the presence of biodiesel-derived glycerol (unpublished results). In this project, wild Saccharomyces cerevisiae strains isolated from the same environment were screened for their potential to produce biodiesel from lignocellulosic residues. The strains that displayed high resistance to common lignocellulosic inhibitors (viz. acetic acid, furfural and 5-hydromethoxyfurfural), were further assessed for lipid production. The strains’ lipid accumulation profiles were evaluated by adding the lipid droplet-specific fluorescent dye BODIPY493/503 to the growth media and measuring growth and fluorescence emission over time using the Biolector. The effects of carbon-to-nitrogen ratio (C/N) and temperature on biomass production and lipid accumulation were also assessed, in order to define the optimal lipid accumulation-inducing conditions for each strain. The best performing strains were further characterized using GC-MS and GC-FID, to identify and quantify the main fatty acids present in the lipids. The best performing S. cerevisiae strains show high potential for application in biodiesel production, presenting high lipid accumulation over a wide range of C/N and temperatures.