Towards a Microbial Production of Fatty Acids as Precursors of Biokerosene from Glucose and Xylose

Abstract

The aviation industry considers the development of sustainable biofuels as one of the biggest challenges of the next ten years. The aim is to lower the environmental impact of the steadily increasing use of fossil fuels on climate change, yielding greater energy independence and fuel security. Thus, the development of a new route for the production of lipids from renewable non-food resources is now being promoted with the recent ASTM certification of hydrotreated oils. Our study focuses on the potential of growth of the oleaginous yeast Rhodotorula glutinis using glucose and xylose which can come from renewable lignocellulosic substrates and of lipid accumulation using glucose as substrate. Experiments were carried out in fed-batch mode which allowed feed flux management. Carbon fluxes were controlled with modifying xylose/glucose ratios to quantify metabolism in optimal growth condition. Besides, the management of carbon and nitrogen fluxes allowed characterizing lipid accumulation. Thus, it has been shown that the yeast Rhodotorula glutinis can simultaneously consume glucose and xylose. When the ratio xylose/glucose increased, the growth rate and the carbon conversion yield into biomass decreased: it was of 0.36 h-1 and 0.64 Cmol x* .Cmol glu -1 for pure glucose, it was of 0.15 h-1 and 0.56 Cmol .Cmol -1 for 10% xylose and it was of 0.037 h-1 and 0.18 Cmol .Cmol -1 for pure xylose. The necessity to maintain residual growth and to manage carbon fluxes to optimize lipid accumulation performance was revealed. Lipid accumulation on glucose engendered a final biomass concentration of 150 gCDW .L-1 , microbial production (72% of lipids) and maximal productivity over 1.48 glip .L-1 .h-1 . The culture temperature is an important parameter to modulate the lipid profile. The results were encouraging. Lipid accumulation using lignocellulosic feedstock was shown to be a highly promising route.