Sphingolipids: A potential key to acetic acid resistance in Zygosaccharomyces bailii

Biomass derived products will play a significant role in the development towards a sustainable society. One major issue in the production of bio-based chemicals, using microorganisms as cell-factories, is the high and therefore inhibitory concentration of acetic acid, released during pretreatment of lignocellulose raw material. Acetic acid toxicity in Saccharomyces cerevisiae has been explained by reduced intracellular pH [1], accumulation of the acetate anion [2], and signaling effects triggering cell death [3]. The undissociated form of acetic acid enters the cell by passive diffusion over the lipid bilayer, although recent publications also suggest the involvement of Fps1p, aquaglyceroporin channel in the acetate uptake [4]. The aim of the present study is to investigate the potential relationship between plasma membrane lipid composition and acetic acid resistance, in the two yeasts S. cerevisiae and Zygosaccharomyces bailii. Z. bailii is a common food spoilage yeast, typically isolated from acetic acid rich environments such as vinegar or pickles and is used in this study as a model for acetic acid resistance. Previous publications demonstrated that Z. bailii unlike S. cerevisiae exhibit retained intracellular pH [5] and plasma membrane integrity [6] upon exposure to acetic acid. Detailed lipidomic profiling of glycerophospholipids, sphingolipids and sterols using multiple-reaction-monitoring mass spectrometry (MRM-MS) has been performed with total lipids extracts from S. cerevisiae and Z. bailii cultured in the absence and presence of acetic acid. Lipidome analysis pointed out sphingolipids as a key mediator in acetic acid resistance with strong increase in both S. cerevisiae and Z. bailii, when cultured with acetic acid. First, the basal levels of complex sphingolipids were 13 times higher in Z. bailii, possibly explaining the higher acetic acid resistance of this yeast species in comparison to S. cerevisiae. Moreover Z. bailii showed an astounding ability to remodel its membrane composition upon acetic acid stress, with strong increase in complex sphingolipids and a drastic reduction of glycerophospholipids. The next step of this study will be to use the lipid data to develop a strategy to engineer the lipid metabolism of S. cerevisiae towards increased acetic acid resistance. [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] Mollapour et al. Mol Cell Biol (2007) 27(18):6446, [5] Arneborg et al. Archives of Microbiology (2000) 174(1-2):125, [6] Prudêncio et al. Cytometry (1998) 31(4):30