Metabolic insights into the yeast response to propionic acid based on high resolution 1H NMR spectroscopy

Abstract

The experimental model Saccharomyces cerevisiae has been widely used to elucidate the molecular mechanisms behind resistance to weak acids in fungi, an essential knowledge for the development of more suitable preservation strategies. Previous studies, based on transcriptomic and chemogenomic approaches, revealed a number of yeast responses to propionic acid, widely used in the preservation of bakery and fresh dairy products. In the present work we report the metabolic changes occurring during yeast adaptation to, and growth in, the presence of this weak acid (20 mM at pH 4) using high resolution 1H NMR spectroscopy coupled with multivariate statistical analysis. The metabolic profiles highlighted the separation of propionic acid-induced lag-phase in two parts. The initial period of incubation under acid stress (up to 3 h following the inoculation of an unadapted yeast population) was characterized by a decrease of cell viability and of the average intracellular pH (pHi) values. The final part of this incubation period (from 4 to 6 h of incubation) was characterized by the start of cell division in the presence of the acid, an increase of the average pHi and a metabolic profile close to the profile exhibited by cells in the exponential phase of growth in propionic acid supplemented medium. An association between the average pHi values and the levels of glutamate and propionate during growth latency was identified. Changes in the cell content in other amino acids, ATP, NAD+, glycerol and trehalose were also registered during yeast incubation with propionic acid. These alterations are discussed in the context of the global response to this weak acid.