Lipid production from hemicellulose hydrolysate and acetic acid by Lipomyces starkeyi and the ability of yeast to metabolize inhibitors

Abstract

Sugarcane bagasse (SCB) represents a potentially less expensive and renewable source of fermentable sugars that can be converted into biofuels and chemicals. Microbial conversion of the hemicellulose fraction is essential for increased biofuel production, and microorganisms able to overcome the difficulties imposed by inhibitors generated during hydrolysis of the hemicellulosic fraction are desirable for this purpose. Lipomyces starkeyi, cultivated in hemicellulosic hydrolysate (HH) from sugarcane bagasse composed of 14.0g/L xylose, 2.9g/L glucose, 2.6g/L arabinose, 2.6g/L acetic acid, 0.04g/L furfural and 0.02g/L 5-hydroxymethylfurfural (HMF), was not inhibited by HMF, furfural or acetic acid. Furthermore, the inhibitors were depleted during fermentation, possibly due to yeast metabolism. This assumption was supported by analysis of the L. starkeyi genome, which confirmed the presence of key genes related to inhibitor metabolism. Furthermore, a preliminary fermentation using only acetic acid as the carbon source indicated that L. starkeyi was able to use acetic acid (∼3.0g/L) for cell growth (0.9g/L) and biosynthesis of lipids (28.4%,w/w). L. starkeyi showed favorable and robust characteristics as a promising microorganism able to convert HH sugars into lipids without previous detoxification.