Tools development for the recycling of lignocellulosic biomass in yeast

Abstract

Syngas fermentation is a bioconversion technology of syngas/waste gas components to produce lowcarbon molecules. This technology is currently undergoing an intensive research and development phase.Acetogens (Clostridium, Eubacterium, Moorella) have been shown to ferment single carbon gases such as CO and CO2 plus H2 into chemicals (mainly acetate, ethanol, lactate or 2,3-BDO)through the acetyl-CoA pathway (Wood–Ljungdahl pathway). M. thermoacetica has great potential as microbial production platforms using syngas, because it has high growth and metabolism rates and low microbial contamination rates due to their high growth temperature. Here we describe a strategy for the gas fermentation using M. thermoacetica and a pressurized gas fermenter aimed to improve the overall reaction rate as well as the global yield of the process for the production of acetate. In a second fermentation stage, we investigated the use of acetate as main carbon source for the production of triacylglycerides (TAGs) using the oleaginous yeast Yarrowia lipolytica. This microorganism can accumulate in the form of lipid bodies, lipids of up to 60% wt/wt of their biomass. Fermentation conditions were studied at laboratory level to determine the most important parameters influencing lipid accumulation (pH, DO, C/N ratio) as well as alternative carbon sources to increase the yield of lipid production. For this purpose, not only batch and fed-batch fermentation processes but also continuous fermentations with cell recycle, fed with a diluted acetate solution,were carried out at lab scale using bench scale bioreactors of 1.5 L. The overall results showed that acetate produced from syngas can be used as promising, low-cost carbon source for growth and lipid production in Y. lipolytica, which can be further processed to obtain sustainable biofuels.