A Physiological Characterization in Controlled Bioreactors Reveals a Novel Survival Strategy for Debaryomyces hansenii at High Salinity

Debaryomyces hansenii is traditionally described as a halotolerant non-conventional yeast, and has served as a model organism for the study of osmo- and salt tolerance mechanisms in eukaryotic systems for the past 30 years. However, unravelling of D. hansenii´s biotechnological potential has always been difficult due to the persistent limitations in the availability of efficient molecular tools described for this yeast. Additionally, there is a lack of consensus and contradictory information along the recent years that limits a comprehensive understanding of its central carbon metabolism, mainly due to a lack of physiological studies in controlled and monitored environments. Moreover, there is little consistency in the culture conditions (media composition, temperature and pH among others) used by different groups, which makes it complicated when trying to get prevalent conclusions on behavioural patterns. In this work, we present for the first time a characterization of D. hansenii in batch cultivations using highly controlled lab-scale bioreactors. Our findings contribute to a more complete picture of the central carbon metabolism and the external pH influence on the yeast’s ability to tolerate high Na+ and K+ concentrations, pointing to a differential effect of both salts, as well as a positive effect in cell performance when low environmental pH values are combined with a high sodium concentration in the media. Finally, a novel survival strategy at very high salinity (2 M) is proposed for this yeast, as well as potential outcomes for its use in industrial biotechnology applications.