A new system for synthesis and secretion of oils in yeasts

Microbial lipids represent renewable, biodegradable, sustainable alternatives to petroleum. Yeast lipids are particularly appealing due to fast growth rates and high lipid yields. However, challenges include high costs of substrates and downstream processing. We identified several pink Basidiomycetous yeasts in the Phaff Yeast Culture Collection capable of simultaneously accumulating high intracellular lipids in the form of triacylglycerol (TAG), and extracellular secreted lipids in the form of glycolipids. In the present work we show that these yeasts secrete up to 12 g/L glycolipid when grown in lab media containing 50 g/L glucose. Similar yields were also obtained when grown on other substrates such as sucrose, glycerol or molasses.  The secreted product is a hydroxylated fatty acid conjugated to a disaccharide of glucose. The glycolipid spontaneously phase separates and settles to the bottom of the vessel, simplifying its recovery. These molecules display biosurfactant activity, and can therefore be used either as precursors to biodiesel and other oleochemicals, or as biosurfactants in cleaners, cosmetics and personal care products. Starmerella bombicola, an ascomycetous yeast, is a well known producer of similar glycolipids. Advantages of our yeasts are that they do not require expensive combinations of lipophilic plus hydrophilic substrates or costly solvent extraction, and they simultaneously accumulate intracellular TAG in significant amounts, up to 50% of cell dry weight. The discovery and utilization of these yeasts constitutes a biodegradable, sustainable alternative to petroleum based fuels and oleochemicals, using cheaper feedstocks and simplified recovery techniques compared to other microbial oil technologies such as algae.