Mechanism of Yeast Adaptation to Weak Organic Acid Stress

Abstract

The budding yeast Saccharomyces cerevisiae has great potential to tolerate weak organic acid stress. This trait is becoming important for refining bioproduction systems for chemicals such as lactic acid. In this chapter, we summarize mechanisms of S. cerevisiae adaptation to weak organic acids. For example, yeast cells counteract lipophilic organic acids such as benzoic or sorbic acid by enhancing the production of plasma membrane transporters, including Pdr12, which pump the acid anions out of cells. For acetic acid stress, a less lipophilic organic acid, yeast cells increase their resistance through inactivation of the plasma membrane channel Fps1, which facilitates diffusional entry of acetic acid. On the other hand, protons generated by dissociation of weak organic acids are actively pumped out of the cell by the plasma membrane proton transporter Pma1. During the period of adaptation, the transcription activators War1 and Haa1 are important in stimulating transcription-mediated adaptation responses. Haa1 is also essential to activate the adaptation response to lactic acid stress. Our recent analysis suggested that one of the adaptation responses to lactic acid stress is mediated by nuclear localization of Haa1. This nuclear localization is thought to be linked to the extent of Haa1 phosphorylation, which seems to be important for Msn5-mediated nuclear export of Haa1. Studies for improving lactic acid resistance are also discussed from the point of view of efficient lactic acid production by S. cerevisiae.