Generic and specific transcriptional responses to different weak organic acids in anaerobic chemostat cultures of<i>Saccharomyces cerevisiae</i>

Self Cite

Based on the high acid tolerance and the simple nutritional requirements of Saccharomyces cerevisiae, engineered strains of this yeast are considered biocatalysts for industrial production of high-purity undissociated lactic acid. However, high concentrations of lactic acid are toxic to S. cerevisiae, thus limiting its growth and product formation. Physiological and transcriptional responses to high concentrations of lactic acid were studied in anaerobic, glucose-limited chemostat cultures grown at different pH values and lactic acid concentrations, resulting in a 50% decrease in the biomass yield. At pH 5, the yield decrease was caused mostly by osmotically induced glycerol production and not by the classic weak-acid action, as was observed at pH 3. Cultures grown at pH 5 with 900 mM lactic acid revealed an upregulation of many genes involved in iron homeostasis, indicating that iron chelation occurred at high concentrations of dissociated lactic acid. Chemostat cultivation at pH 3 with 500 mM lactate, resulting in lower anion concentrations, showed an alleviation of this iron homeostasis response. Six of the 10 known targets of the transcriptional regulator Haa1p were strongly upregulated in lactate-challenged cultures at pH 3 but showed only moderate induction by high lactate concentrations at pH 5. Moreover, the haa1⌬ mutant exhibited a growth defect at high lactic acid concentrations at pH 3. These results indicate that iron homeostasis plays a major role in the response of S. cerevisiae to high lactate concentrations, whereas the Haa1p regulon is involved primarily in the response to high concentrations of undissociated lactic acid.

Section: Vol 74 2008 Yeast Responses To Lactic Acid 5763mentioning

confidence: 64%

mentioning

confidence: 99%

See 1 more Smart Citation

Physiological and Transcriptional Responses to High Concentrations of Lactic Acid in Anaerobic Chemostat Cultures of Saccharomyces cerevisiae

Abbott

Suir

Maris

et al. 2008

Self Cite

“…Our data show that two classes of differentially regulated transporters, multidrug resistance efflux pumps (especially the MATE transporters with associated TetR family repressors) and ABC transporters, likely have critical, but uncharacterized, roles in L. monocytogenes resistance to organic acid stress. Transporters are important in the yeast organic acid stress response, where Saccharomyces cerevisiae strongly downregulated membrane transporters in response to acetic acid stress (1). In Acetobacter aceti, resistance to acetic acid was reduced upon deletion of a putative ABC transporter (46).…”

Section: Discussionmentioning

confidence: 99%

The Transcriptional Response of Listeria monocytogenes during Adaptation to Growth on Lactate and Diacetate Includes Synergistic Changes That Increase Fermentative Acetoin Production

Stasiewicz

Wiedmann

Bergholz

2011

The organic acids lactate and diacetate are commonly used in combination in ready-to-eat foods because they show synergistic ability to inhibit the growth of Listeria monocytogenes. Full-genome microarrays were used to investigate the synergistic transcriptomic responses of two L. monocytogenes strains, H7858 (serotype 4b) and F6854 (serotype 1/2a), to these two organic acids under conditions representing osmotic and cold stress encountered in foods. Strains were exposed to brain heart infusion (BHI) broth at 7°C with 4.65% water-phase (w.p.) NaCl at pH 6.1 with (i) 2% w.p. potassium lactate, (ii) 0.14% w.p. sodium diacetate, (iii) the combination of both at the same levels, or (iv) no organic acids as a control. RNA was extracted 8 h after exposure, during lag phase, to capture gene transcription changes during adaptation to the organic acid stress. Significant differential transcription of 1,041 genes in H7858 and 640 genes in F6854 was observed in at least one pair of the 4 different treatments. The effects of combined treatment with lactate and diacetate included (i) synergistic transcription differences for 474 and 209 genes in H7858 and F6854, respectively, (ii) differential transcription of genes encoding cation transporters and ABC transporters of metals, and (iii) altered metabolism, including induction of a nutrient-limiting stress response, reduction of menaquinone biosynthesis, and a shift from fermentative production of acetate and lactate to energetically less favorable, neutral acetoin. These data suggest that additional treatments that interfere with cellular energy generation processes could more efficiently inhibit the growth of L. monocytogenes.Listeria monocytogenes is a psychrotolerant food-borne pathogen that is of particular concern to the ready-to-eat-meat and -seafood industries because its ability to grow at temperatures as low as Ϫ0.4°C (70) reduces the ability of refrigeration to control the pathogen's growth in foods. Because L. monocytogenes generally contaminates foods at low levels (27) and has a high infectious dose (69), the ability of the organism to grow in foods is critical for its ability to cause disease (16). Foods do not support growth if they are stored frozen, have a pH of Յ4.4, have a water activity of Ͻ0.92, or incorporate some type of growth inhibiting measure (21), e.g., chemical preservatives (32). Ready-to-eat meat and seafood products have been identified as high-risk foods for listeriosis, as these foods support growth of L. monocytogenes (22), but it has also been predicted that reformulation of U.S. deli meats with effective growth inhibitors, e.g., the organic acids lactate and diacetate, would result in a 2-to 8-fold reduction of listeriosis due to consumption of these products (55). One particular advantage to using the combination of lactate and diacetate for L. monocytogenes control in meat and seafood products is that these inhibitors have been shown to have greater-than-additive, i.e., synergistic, growth-inhibiting effects (65), although the mechanisms...

“…Sampling of cells from fermentations and total RNA extraction were performed as described by Abbott et al (1). Probe preparation and hybridization to Affymetrix Genechip microarrays were performed according to Affymetrix instructions, starting with 6 g of total RNA.…”

mentioning

confidence: 99%

Comparative Transcriptomic Approach To Investigate Differences in Wine Yeast Physiology and Metabolism during Fermentation

Rossouw

Olivares-Hernandes

Nielsen

et al. 2009

Commercial wine yeast strains of the species Saccharomyces cerevisiae have been selected to satisfy many different, and sometimes highly specific, oenological requirements. As a consequence, more than 200 different strains with significantly diverging phenotypic traits are produced globally. This genetic resource has been rather neglected by the scientific community because industrial strains are less easily manipulated than the limited number of laboratory strains that have been successfully employed to investigate fundamental aspects of cellular biology. However, laboratory strains are unsuitable for the study of many phenotypes that are of significant scientific and industrial interest. Here, we investigate whether a comparative transcriptomics and phenomics approach, based on the analysis of five phenotypically diverging industrial wine yeast strains, can provide insights into the molecular networks that are responsible for the expression of such phenotypes. For this purpose, some oenologically relevant phenotypes, including resistance to various stresses, cell wall properties, and metabolite production of these strains were evaluated and aligned with transcriptomic data collected during alcoholic fermentation. The data reveal significant differences in gene regulation between the five strains. While the genetic complexity underlying the various successive stress responses in a dynamic system such as wine fermentation reveals the limits of the approach, many of the relevant differences in gene expression can be linked to specific phenotypic differences between the strains. This is, in particular, the case for many aspects of metabolic regulation. The comparative approach therefore opens new possibilities to investigate complex phenotypic traits on a molecular level.Saccharomyces cerevisiae is a preferred model organism for studying eukaryotic cells. The haploid yeast genome is compact (12 to 13.5 megabases) and contains only around 6,000 proteinencoding genes (18). However, the functional analysis of the yeast genome remains a challenge, predominantly because many of the putative protein-encoding genes appear not to be amenable to classical genetic approaches. One possible reason is that most studies have been limited to a small number of laboratory strains. While these strains have been selected for their ease of use under laboratory conditions, they lack many of the characteristics that are prominent in industrial isolates of this species. These industrial strains are highly diverse since they have been selected for a large number of different and highly specific tasks. This geno-and phenotypic diversity represents a largely untouched genetic resource. Some of the challenges of large-scale functional genomics can therefore likely be met by including such strains in comparative transcriptomic studies (21, 25).In commercial wine fermentations, the yeast species S. cerevisiae is the major role player, and wine yeast strains have been isolated and selected for optimized performance in certain key areas of oeno...