Physiological characteristics of low pH tolerance of an endophytic Saccharomyces cerevisiae strain isolated from Usnea sp. and exploration of the underlying molecular mechanism

Abstract:

[Objective] To detect the physiological characteristics related to organic acid production and low pH tolerance of the endophytic Saccharomyces cerevisiae 2-2 strain isolated from Usnea sp. in Tibet, China, and explore the molecular mechanism. [Methods] The pH of different strains was compared during liquid fermentation using different initial sugar concentrations, and the growth under stress conditions was monitored. The organic acid production potential and low pH resistance characteristics of S. cerevisiae strains were detected. Comparative genomic analysis was performed to explore the molecular mechanism of acid production and acid tolerance of S. cerevisiae strain 2-2 by real-time fluorescence quantitative polymerase chain reaction (RT-qPCR). [Results] S. cerevisiae 2-2 had higher acid-producing potential among the tested yeast strains, which also showed better acid tolerance than that of the model strain S. cerevisiae strain S288C. The transcription levels of PDR15, PDR12 and SUR1 that affect the acid stress tolerance of S. cerevisiae in 2-2 were up-regulated or down-regulated under acid stress conditions, but the trends of these key genes were opposite to that of the strain S288C. [Conclusion] Endophytic S. cerevisiae 2-2 is a strain with potential in organic acid production and shows strong tolerance to low pH. An in-depth analysis of its unique regulatory mechanism will benefit the development of acid-producing yeast strains with improved performance.