Epigenetic Response of Yarrowia lipolytica to Stress: Tracking Methylation Level and Search for Methylation Patterns via Whole-Genome Sequencing.

Abstract

DNA methylation is a common, but not universal, epigenetic modification that plays an important role in multiple cellular processes. While definitely settled for numerous plant, mammalian, and bacterial species, the genome methylation in different fungal species, including widely studied and industrially-relevant yeast species, Yarrowia lipolytica, is still a matter of debate. In this paper, we report a differential DNA methylation level in the genome of Y. lipolytica subjected to sequential subculturing and to heat stress conditions. To this end, we adopted repeated batch bioreactor cultivations of Y. lipolytica subjected to thermal stress in specific time intervals. To analyze the variation in DNA methylation between stressed and control cultures, we (a) quantified the global DNA methylation status using an immuno-assay, and (b) studied DNA methylation patterns through whole-genome sequencing. Primarily, we demonstrated that 5 mC modification can be detected using a commercial immuno-assay, and that the modifications are present in Y. lipolytica’s genome at ~0.5% 5 mC frequency. On the other hand, we did not observe any changes in the epigenetic response of Y. lipolytica to heat shock (HS) treatment. Interestingly, we identified a general phenomenon of decreased 5 mC level in Y. lipolytica’s genome in the stationary phase of growth, when compared to a late-exponential epigenome. While this study provides an insight into the subculturing stress response and adaptation to the stress at epigenetic level by Y. lipolytica, it also leaves an open question of inability to detect any genomic DNA methylation level (either in CpG context or context-less) through whole-genome sequencing. The results of ONT sequencing, suggesting that 5 mC modification is either rare or non-existent in Y. lipolytica genome, are contradicted with the results of the immunoassay.