Protein aggregation and membrane lipid modifications under lactic acid stress in wild type and OPI1 deleted Saccharomyces cerevisiae strains

Abstract

BackgroundLactic acid is a versatile chemical platform with many different industrial applications. Yeasts have been demonstrated as attractive alternative to natural lactic acid producers since they can grow at low pH, allowing the direct purification of the product in the desired acidic form. However, when very high concentrations of organic acids are reached, the major limitation for a viable production is the toxic effect of the product. The accumulation in the cytosol of H+ and of the weak organic counter-anions triggers a cellular reprogramming. Here, the effects of lactic acid exposure on Saccharomycescerevisiae have been evaluated by Fourier transform infrared (FTIR) microspectroscopy. In addition to -omic techniques, describing these responses in terms of systems and networks, FTIR microspectroscopy allows a rapid acquisition of the cellular biochemical fingerprint, providing information on the major classes of macromolecules.ResultsFTIR analyses on Saccharomyces cerevisiae cells under lactic acid stress at low pH revealed some still uncharacterized traits: (1) a direct correlation between lactic acid exposure and a rearrangement in lipid hydrocarbon tails, together with a decrease in the signals of phosphatidylcholine (PC), one of the main components of cell membrane; (2) a rearrangement in the cell wall carbohydrates, including glucans and mannans (3) a significant yet transient protein aggregation, possibly responsible for the observed transient decrease of the growth rate. When repeated on the isogenic strain deleted in OPI1, encoding for a transcriptional repressor of genes involved in PC biosynthesis, FTIR analysis revealed that not only the PC levels were affected but also the cell membrane/wall composition and the accumulation of protein aggregates, resulting in higher growth rate in the presence of the stressing agent.ConclusionsThis work revealed novel effects evoked by lactic acid on cell membrane/wall composition and protein aggregation in S. cerevisiae cells. We consequently demonstrated that the targeted deletion of OPI1 resulted in improved lactic acid tolerance. Considering that stress response involves many and different cellular networks and regulations, most of which are still not implemented in modelling, these findings constitute valuable issues for interpreting cellular rewiring and for tailoring ameliorated cell factories for lactic acid production.Electronic supplementary materialThe online version of this article (doi:10.1186/s12934-016-0438-2) contains supplementary material, which is available to authorized users.

Physiological and Metabolomic Analysis of Issatchenkia orientalis MTY1 With Multiple Tolerance for Cellulosic Bioethanol Production

“…In additions, recombinant S. cerevisiae strains overexpressing the HAA1 gene or deficient in the OPI1 gene possessed higher tolerance on acetic acid or lactic acid, respectively. Especially, the deletion of OPI1 gene in S. cerevisiae affected the components of cell membrane and wall, and accumulated protein aggregation, resulting in increased tolerance on lactic acid . S. cerevisiae YZ2 constructed by genome shuffling technique showed an improvement in cell viability and ethanol production under the presence of acetic acid .…”

“…By a series of screening methods, metabolic engineering and evolutionary engineering, mutant or recombinant strains of conventional ( Saccharomyces cerevisiae ), and non‐conventional yeasts ( Zygosaccharomyces bailii, Kluyveromyces marxianus and Hansenula polymorpha ) have been developed to be able to grow over 40–45 °C or in the presence of 24 g L −1 weak acid . In additions, recombinant S. cerevisiae strains overexpressing the HAA1 gene or deficient in the OPI1 gene possessed higher tolerance on acetic acid or lactic acid, respectively. Especially, the deletion of OPI1 gene in S. cerevisiae affected the components of cell membrane and wall, and accumulated protein aggregation, resulting in increased tolerance on lactic acid .…”

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