Molecular mechanisms behind acetic acid resistance: Insights from Zygosaccharomyces bailii

Biomass derived products will play a significant role in the development towards a sustainable society. The feasibility of the production of bio-based chemicals relies on robust industrial microorganisms. One major issue reducing process productivity is the high concentration of acetic acid, released during pretreatment of lignocellulose raw material. Acetic acid effect on yeast has been widely investigated: reduced intracellular pH [1], accumulation of the acetate anion [2], and signaling effects triggering cell death [3] are some of the mechanisms indicated as responsible for its toxicity. Zygosaccharomyces bailii is a yeast species that tolerates low pH and high concentrations of weak organic acids [4]. It is a common food spoilage yeast, typically isolated from acetic acid rich environments such as vinegar or pickles. Z. bailii is extensively investigated from a food science perspective, for the development of food preservatives. Its potential for industrial applications as a model organism for acetic acid resistance has been less investigated. Its tolerance has been explained to some extent by retained intracellular pH and plasma membrane integrity [5,6], specific acetate transporter supporting growth on acetate even in the presence of glucose [7], and higher metabolic flux through the unique ZbACS2 acetyl-CoA syntethase [8]. In the present study, the metabolic response of Z.bailii (CBS 7555) to acetic acid was characterized in a comparative investigation together with Saccharomyces cerevisiae (CEN.PK.0113_7D). Fermentation results indicate that S. cerevisiae tolerates significantly lower acetic acid concentrations compared to Z. bailii. Acetic acid affected S. cerevisiae mainly by decreasing maximum specific growth rate and specific substrate consumption rate. Z. bailii on the other hand was mainly affected by an increased lag phase. Z. bailii displayed sustained growth at acetic acid concentrations as high as 36 g/L, while concentrations above 9 g/L severely decreased the maximum specific growth rate of S. cerevisiae. The molecular mechanisms behind acetic acid resistance in Z. bailii are currently being investigated in order to formulate strategies to improve acetic acid tolerance in S. cerevisiae.References[1] Casal et al. FEMS Microbiol Rev (2008) 32(6): 974[2] Russel. J. Appl Bacteriol (1992) 73: 363[3] Ludovico et al. Microbiology (2001) 147:2409[4] Fleet G. Crit. Rev. Biotechnol (1992) 12: 1[5] Arneborg et al. Arch Microbiol (2000) 174:125[6] Prudenico et al. Cytometry (1998) 31:307[7] Sousa et al. Appl. Environ. Microbiol. (1996) 62:3152[8] Rodrigues et al. PLOSone (2012) 7(12): e5240