Transcriptional profiling of Rhodotorula toruloides IST536 and derived evolved strain IST536 MM15 under non-stressing conditions
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 Overall design: mRNA profiling of R. toruloides IST536 and the derived evolved strain IST536 MM15 unstressed cells. A total of 4 samples were analysed (2 biological replicates)