Project description:The oleaginous red yeast species Rhodotorula toruloides, a prominent environmental basidiomycetous yeast, has garnered significant interest for its remarkable capacity to utilize main carbon sources present in lignocellulosic hydrolysates, such as glucose, xylose, and acetic acid, and to efficiently produce lipids and carotenoids. This species can also efficiently use other less usual and difficult-to-catabolize C-sources, as is the case of the acid sugar D-galacturonic acid and the neutral sugar L-arabinose, present in hydrolysates from pectin-rich agro-industrial residues. Strain R. toruloides IST536 (alias PYCC 5615) was previously selected in our laboratory for sugar beet pulp valorization based on its ability to produce lipids and carotenoids through the complete catabolism of the major C-sources present in the hydrolysates (1). This strain, whose genome has been recently sequenced in our laboratory, is a conjugated strain derived from IFO 0559 (isolated from wood-pulp; GCA_000988805.1) × IFO 0880 (isolated from air; GCA_001255795.1) (2). Despite its potential, the metabolism of this promising strain can be limited by the presence of acetic acid in the hydrolysates as well as other inhibitors present in lignocellulosic hydrolysates. To increase IST536 (PYCC 5615) strain robustness, an adaptive laboratory evolution (ALE) strategy was used. The selected evolved strain IST536 MM15 exhibits increased tolerance to several inhibitors of biotechnological relevance: methanol and the four main inhibitors present in lignocellulosic hydrolysates: acetic and formic acids, hydroxymethylfurfural (HMF), and furfural (3). The superior performance of this evolved multi-stress tolerant strain for lipid production from non-detoxified lignocellulosic biomass hydrolysates was confirmed. To obtain mechanistic insights underlying such multi-tolerant phenotype, the genomes of the original and the evolved strains, IST536 (PYCC 5615) and IST536 MM15, respectively, were sequenced and the transcriptomic profiling of both strains under non-stressing conditions was performed. References: 1. Martins LC, et, al. Journal of Fungi. 2021; 7(3):215. https://doi.org/10.3390/jof7030215 2. Banno, I. (1967). The Journal of General and Applied Microbiology, 13(2), 167-196. https://doi.org/10.2323/jgam.13.167 3. Fernandes, M. A., Mota, M. N., et al, Journal of Fungi, 2023, 9(11), 1073 https://doi.org/10.3390/jof9111073
Project description:The use of cell factories to convert sugars from lignocellulosic biomass into chemicals in which oleochemicals and food additives, such as carotenoids, play an important role is essential for the shift towards sustainable processes. Rhodotorula toruloides is a yeast that naturally metabolises a wide range of substrates, including lignocellulosic hydrolysates, and converts them into lipids and carotenoids. In this study, xylose, the main component of hemicellulose, was used as the sole substrate for R. toruloides, and a detailed physiology characterisation combined with absolute proteomics and genome-scale metabolic models was carried out to understand the regulation of lipid and carotenoid production. To improve these productions, oxidative stress was induced by hydrogen peroxide and light irradiation and further enhanced by adaptive laboratory evolution. Based on the online measurements of growth and CO2 excretion, three distinct growth phases were identified during batch cultivations. The intracellular flux estimations correlated well with the measured protein levels and demonstrated improved NADPH regeneration and phosphoketolase activity and reduced beta-oxidation, correlating with increasing lipid yields. Light irradiation conditions resulted in 70% higher carotenoid and 40% higher lipid yields. The presence of hydrogen peroxide did not affect the carotenoid yield but culminated in the highest lipid yield of 0.65 ± 0.06 g/gDCW. The adapted strain showed improved fitness and 130% higher carotenoid yield than the parental strain. This work presented a holistic view of xylose conversion into microbial oil and carotenoids by R. toruloides for further cost-effective and renewable production of these molecules.