Unveiling the genetic basis of the low pH response in the acidophilic yeast Maudiozyma bulderi (previously Kazachstania bulderi) via transcriptomic analysis

Non-conventional yeasts represent a great genetic and phenotypic diversity with potential for industrial strain development in the bio-production of green chemicals. In recent years, mass genome sequencing of non-conventional yeasts has opened avenues to improved understanding of transcriptional networks and phenotypic plasticity and gene function, including the discovery of novel genes. Here, we investigated the gene expression changes at low-pH in three strains of the acidophilic yeast Maudiozyma bulderi (previously Kazachstania bulderi): CBS8638, CBS8639 and NRRL-Y27205. The comparison of the transcriptome of cells growing in a bioreactor at pH=5.5 vs pH= 2.5, primarily showed dysregulation of genes involved in cell wall integrity, with NRRL-Y27205, the least acidophilic strain, showing the largest transcriptional response when compared to the other two strains. We identified four uncharacterised genes, unique to M. bulderi ,and predicted function as transporters, upregulated at low pH. We also showed that M. bulderi cell wall and membrane lipid composition is not significantly affected by low pH unlike Saccharomyces cerevisiae. Overall, our data on transcriptional variability in M. bulderi highlights genes and cellular pathways involved in the acidophilic adaptation of this species and can aid further strain development.