Toxic effects of fatty acids on yeast cells: dependence of inhibitory effects on fatty acid concentration.

The yeasts Saccharomyces cerevisiae, Candida utilis, and Candida lipolytica were used to investigate the action of different concentrations of fatty acids (from acetic to myristic acid) on cell growth, division, uptake of inorganic phosphate, and substrate oxidation. The former two yeasts were found to undergo an inhibition of growth, cell division, and phosphate uptake at lower acid concentrations and to experience the inhibition of substrate oxidation at higher acid concentrations. The concentration dependence of the action of fatty acids can be classified into four categories: 1) subthreshold concentrations which do not inhibit growth and have either no effect on, or stimulate, oxygen consumption; 2) threshold concentrations which lower the rate of growth, cell division, and phosphate uptake but do not inhibit the oxidation of carbon substrate; 3) above-threshold concentrations which inhibit partially even substrate oxidation, and 4) microbicide concentrations. Candida lipolytica displays the same sensitivity toward the action of fatty acids as the above yeast species; however, the threshold concentrations are higher and can be quickly lowered owing to oxidation by the yeast. The concentrations of fatty acids found in the medium after cultivations of yeast with n-alkanes are of the same order as limiting concentrations; the formation of acids with twelve and less carbons in the molecule can thus be assumed to be one of the basic reasons for lowering of biomass yields during cultivations on these hydrocarbons.     

Study on fatty acid binding by proteins in yeast. Dissimilar results in Saccharomyces cerevisiae and Yarrowia lipolytica.

1. The presence of soluble proteins with fatty acid binding activity was investigated in cell-free extracts from Saccharomyces cerevisiae and Yarrowia lipolytica cultures. 2. No significant fatty acid binding by proteins was detected in S. cerevisiae, even when grown on a fatty acid-rich medium, thus indicating that such proteins are not essential to fatty acid metabolism. 3. An inducible fatty acid binding protein (K0.5 = 3-4 microM) was found in Y. lipolytica which had grown on a minimal medium with palmitate as the sole source of carbon and energy. 4. The relative molecular mass of this protein was 100,000 as inferred from Sephacryl S-200 gel filtration.     

Yarrowia lipolytica mutants devoid of pyruvate carboxylase activity show an unusual growth phenotype

We have cloned and characterized the gene PYC1, encoding the unique pyruvate carboxylase in the dimorphic yeast Yarrowia lipolytica. The protein putatively encoded by the cDNA has a length of 1,192 amino acids and shows around 70% identity with pyruvate carboxylases from other organisms. The corresponding genomic DNA possesses an intron of 269 bp located 133 bp downstream of the starting ATG. In the branch motif of the intron, the sequence CCCTAAC, not previously found at this place in spliceosomal introns of Y. lipolytica, was uncovered. Disruption of the PYC1 gene from Y. lipolytica did not abolish growth in glucose-ammonium medium, as is the case in other eukaryotic microorganisms. This unusual growth phenotype was due to an incomplete glucose repression of the function of the glyoxylate cycle, as shown by the lack of growth in that medium of double pyc1 icl1 mutants lacking both pyruvate carboxylase and isocitrate lyase activity. These mutants grew when glutamate, aspartate, or Casamino Acids were added to the glucose-ammonium medium. The cDNA from the Y. lipolytica PYC1 gene complemented the growth defect of a Saccharomyces cerevisiae pyc1 pyc2 mutant, but introduction of either the S. cerevisiae PYC1 or PYC2 gene into Y. lipolytica did not result in detectable pyruvate carboxylase activity or in growth on glucose-ammonium of a Y. lipolytica pyc1 icl1 double mutant.     

Mutants of Saccharomyces cerevisiae deficient in acyl-CoA synthetases secrete fatty acids due to interrupted fatty acid recycling

In the present study, acyl-CoA synthetase mutants of Saccharomyces cerevisiae were employed to investigate the impact of this activity on certain pools of fatty acids. We identified a genotype responsible for the secretion of free fatty acids into the culture medium. The combined deletion of Faa1p and Faa4p encoding two out of five acyl-CoA synthetases was necessary and sufficient to establish mutant cells that secreted fatty acids in a growth-phase dependent manner. The mutants accomplished fatty acid export during exponential growth-phase followed by fatty acid re-import into the cells during the stationary phase. The data presented suggest that the secretion is driven by an active component. The fatty acid re-import resulted in a severely altered ultrastructure of the mutant cells. Additional strains deficient of any cellular acyl-CoA synthetase activity revealed an almost identical phenotype, thereby proving transfer of fatty acids across the plasma membrane independent of their activation with CoA. Further experiments identified membrane lipids as the origin of the observed free fatty acids. Therefore, we propose the recycling of endogenous fatty acids generated in the course of lipid remodelling as a major task of both acyl-CoA synthetases Faa1p and Faa4p.     

Mechanism of action of the antibiotic thiolactomycin inhibition of fatty acid synthesis of Escherichia coli

Thiolactomycin, an antibiotic with the structure of (4S)-(2E,5E)-2,4,6-trimethyl-3-hydroxy-2,5,7-octatriene-4-thiolide, inhibits the incorporation of [14C]acetate into cellular fatty acids of Escherichia coli. This antibiotic inhibits the fatty acid synthetase system of E. coli. However, the fatty acid synthetases from Saccharomyces cerevisiae, Candida albicans and rat liver are insensitive to thiolactomycin. This effect may account for the antibacterial activity of thiolactomycin and for its low toxicity in animals.     

Component from the cell surface of the hydrocarbon-utilizing yeast Candida tropicalis with possible relation to hydrocarbon transport.

A polysaccharide-fatty acid complex was isolated from the cell surface of Candida tropicalis growing on alkanes. This complex was solubilized by Pronase treatment of whole cells. A decrease in alkane-binding affinity was observed after Pronase treatment, resulting in 10 to 12% of the yeast dry cell weight being released as polysaccharide. The isolated polysaccharide contained 2.5% fatty acids. C. tropicalis and Saccharomyces cerevisiae grown with glucose contained only traces of fatty acids in the corresponding polysaccharide fraction. The fatty acids were not removed from the polysaccharide moiety by gel filtration. Extraction of the polysaccharide with chloroform-methanol showed that fatty acids were covalently bound to the polysaccharide. The amphipathic nature of the isolated polysaccharide and the hydrocarbon-induced formation suggest a possible role in alkane metabolism.     

Death Resulting from Fatty Acid Starvation in Yeast

Mutants of Saccharomyces cerevisiae having the genotypes fas1 (fatty acid synthetase minus) and fas1, ole1 (fatty acid synthetase and fatty acid desaturase minus) were found to undergo logarithmic death when deprived of required fatty acids, whereas ole1 strains did not. During the first 2 to 3 h of fatty acid starvation, macromolecular synthesis occurred at apparently normal rates, although cell division stopped by the end of the 1st h. Cell death commenced at approximately the 2nd to the 3rd h, and within 24 h, depending upon conditions, 2 to 4 log orders of death had occurred. The loss of viability was accelerated by the addition of detergent, but could be largely prevented by the interruption of protein synthesis, either by amino acid starvation or by the use of cycloheximide. The possible significance of this phenomenon in terms of membrane biosynthesis is discussed.     

Analysis of fatty acid composition of Candida species by gas-liquid chromatography using a polar column

The fatty acid composition of representative Candida species was examined by gas-liquid chromatography (GLC) using a polar column. The major fatty acids were C14:0, C16:0, C18:0 saturated, C16:1 and C18:1 monoenoic series, with or without C18 polyunsaturated acids (C18:2 and C18:3). In Torulopsis glabrata and Saccharomyces cerevisiae the C18:2 and C18:3 acids were not found, but the C10:0 and C12:0 acids were detected in S. cerevisiae. These results indicated that the Candida genus could be distinguished from Torulopsis and Saccharomyces genera by GLC analysis of fatty acids. Quantitative differences in the fatty acid composition between cells grown at high temperature (37 degrees C) and low temperature (25 degrees C) were found generally in Candida species, and the amounts of C18 polyunsaturated acids (C18:2 and C18:3) increased in the cells grown at 25 degrees C. Each Candida species showed a characteristic profile in fatty acid composition. Determination of the cellular fatty acid composition in Candida species is likely to be useful for the grouping or chemotaxonomy of newer isolates of Candida species.     

Comparison of two fatty acid synthetases from Euglena gracilis variety bacillaris

Two enzyme systems from Euglena gracilis var. bacillaris which catalyze the de novo biosynthesis of fatty acids have been compared. One is a multienzyme complex of high molecular weight which is independent of ACP for activity in vitro, and the other is an ACP-dependent system of discrete enzymes (M. L. Ernst-Fonberg, (1973) Biochemistry12, 2449–2455). The latter activity is present in small amounts in etiolated cells and increases upon exposure of dark-grown cells to light, while multienzyme complex fatty acid synthetase activity decreases by about one-half after 24 hr of exposure to light. Results from the greening of dark-grown cells in the presence of cycloheximide, chloramphenicol, or spectinomycin suggests that the chloroplast ribosomes are involved in the appearance of the ACP-dependent activity; alternatively, the cytoplasmic ribosomes appear to be the site of biosynthesis of the multienzyme complex fatty acid synthetase (or a protein responsible for its activation). The fatty acid synthetase activities from several chloroplast mutants were measured. The ACP-dependent activity was reduced or not present depending on the degree of impairment of chloroplast development, while the multienzyme complex activity in all instances continued to respond to light or darkness.Antibodies against the purified multienzyme complex extensively inhibited its activity whereas the activity of the ACP-dependent system was consistently stimulated. The two enzyme systems are immunologically cross reactive but not identical.     

Possible involvement of acetyl coenzyme A carboxylase as well as fatty acid synthetase in the temperature-controlled synthesis of fatty acids in Saccharomyces cerevisiae

Fatty acid synthetase (FAS) preparations from Saccharomyces cerevisiae cells grown at either 35 or 10 degrees C produced the same products at different temperatures and showed quite similar temperature-dependencies in Arrhenius plots, with break points at 25 degrees C. This break point does not appear to reflect a phase transition of phospholipids present in the purified FAS preparations but rather is associated with protein conformational changes. S. cerevisiae cells grown at 35 degrees C and then shifted to 10 degrees C produced fatty acids with a shorter average chain length than those fatty acids synthesized at 10 degrees C by cells already adapted to 10 degrees C (hyper response). Acetyl-CoA carboxylase activity was relatively higher in the cells grown at 35 degrees C than in the cells grown at 10 degrees C; moreover, fatty acids with longer average chain lengths were synthesized in vitro at higher malonyl-CoA concentrations, which was consistent with the difference in the average chain lengths of newly synthesized fatty acids in cells grown at 35 and 10 degrees C. However, the activity levels of acetyl-CoA carboxylase and fatty acid synthetase alone did not account for the hyper response phenomena.     

Repression of Acetyl-Coenzyme A Carboxylase by Unsaturated Fatty Acids: Relationship to Coenzyme Repression

It has been reported that the level of d-biotin in the growth medium of Lactobacillus plantarum regulates the synthesis of apoacetyl-coenzyme A (CoA) carboxylase; high levels cause repression, and deficient levels effect derepression. In this study, evidence has been obtained which suggests that coenzyme repression by biotin is an indirect effect; i.e., biotin regulates the synthesis of unsaturated fatty acids which are the true repressors of the acetyl-CoA carboxylase. This was observed in an experiment in which long-chain unsaturated fatty acids were added to media containing deficient, sufficient, or excess levels of d-biotin. In every case, independently of the biotin concentration for growth, the unsaturated fatty acids caused a severe repression of the carboxylase. Saturated fatty acids were without effect. The level of oleic acid required to give maximal repression was 50 mug/ml. The free fatty acids had no adverse effect on the activity of the cell-free extracts nor on the permeation of d-biotin into the cell. Saturated and unsaturated fatty acids decreased the rate of holocarboxylase formation from d-biotin and the apoacetyl-CoA carboxylase in the extracts. It is concluded that there are at least three mechanisms that control the acetyl-CoA carboxylase in this organism: (i) indirect coenzyme repression by d-biotin, (ii) repression by unsaturated fatty acids, and (iii) regulation of the activity of the holocarboxylase synthetase by both saturated and unsaturated fatty acids.     

Heterologous production of dihomo-gamma-linolenic acid in Saccharomyces cerevisiae

To make dihomo-gamma-linolenic acid (DGLA) (20:3n-6) in Saccharomyces cerevisiae, we introduced Kluyveromyces lactis Delta12 fatty acid desaturase, rat Delta6 fatty acid desaturase, and rat elongase genes. Because Fad2p is able to convert the endogenous oleic acid to linoleic acid, this allowed DGLA biosynthesis without the need to supply exogenous fatty acids on the media. Medium composition, cultivation temperature, and incubation time were examined to improve the yield of DGLA. Fatty acid content was increased by changing the medium from a standard synthetic dropout medium to a nitrogen-limited minimal medium (NSD). Production of DGLA was higher in the cells grown at 15 degrees C than in those grown at 20 degrees C, and no DGLA production was observed in the cells grown at 30 degrees C. In NSD at 15 degrees C, fatty acid content increased up until day 7 and decreased after day 10. When the cells were grown in NSD for 7 days at 15 degrees C, the yield of DGLA reached 2.19 microg/mg of cells (dry weight) and the composition of DGLA to total fatty acids was 2.74%. To our knowledge, this is the first report describing the production of polyunsaturated fatty acids in S. cerevisiae without supplying the exogenous fatty acids.     

Lipid nutrition of Saccharomyces cerevisiae in winemaking

Biosynthesis of cell membrane lipids is a crucial metabolic pathway for the growth and viability of eucaryotic microorganisms. In Saccharomyces cerevisiae, unsaturated fatty acids and ergosterol synthesis needs molecular oxygen. Stuck and sluggish fermentations are related to this aspect of metabolism and constitute a major problem in the wine industry. Anaerobiosis, when lipids are not available in the growth medium, highly stresses cells. They release lipid biosynthesis metabolites and soon cease to multiply. This paper describes an investigation of the nutritional role of exogenous lipids from inactivated yeast cells (IYCs). Fermentations were carried out in a nitrogen-rich synthetic medium similar to grape juice with glucose and fructose as carbon sources, without lipid sources, and in anaerobiosis. The effect of the addition of IYC was assessed. Cell growth, cell lipid composition, glucose and fructose consumption, and acetic acid production were measured during fermentation. Addition of IYC boosted cell growth and sugar consumption, whereas acetic acid production decreased. Biomass yield was influenced by ergosterol availability and increased when IYCs were added. Fatty acid composition of yeast cells was changed by IYC addition.     

Influence of oxygen on the biosynthesis of cellular fatty acids,sterols and phospholipids during alcoholic fermentation by Saccharomyces cerevisiae and Torulaspora delbrueckii

Saccharomyces cerevisiae and Torulaspora delbrueckii were grown under different O₂ availabilities on grape must. Oxygen requirements for the two yeasts were different: under anaerobic conditions, S. cerevisiae produced a higher percentage of unsaturated fatty acids, and had a greater cell yield and fermentation activity than T. delbrueckii. Addition of ergosterol (25mg/l) and oleic acid (31mg/l) caused total recovery of cellular growth and the fermentation activity of S. cerevisiae in anaerobiosis, but not of T. delbrueckii. However a short period of aeration to a 48 h culture in anaerobiosis, led to total recovery of the cellular growth and fermentation activity in both yeasts. Likewise, the effect of a short aeration period on unsaturated fatty acid biosynthesis was similar for both species.     

Isolation of a Saccharomyces cerevisiae long chain fatty acyl:CoA synthetase gene (FAA1) and assessment of its role in protein N- myristoylation

Regulation of myristoylCoA pools in Saccharomyces cerevisiae plays an important role in modulating the activity of myristoylCoA:protein N-myristoyltransferase (NMT), an essential enzyme with an ordered Bi Bi reaction that catalyzes the transfer of myristate from myristoylCoA to greater than or equal to 12 cellular proteins. At least two pathways are available for generating myristoylCoA: de novo synthesis by the multifunctional, multisubunit fatty acid synthetase complex (FAS) and activation of exogenous myristate by acylCoA synthetase. The FAA1 (fatty acid activation) gene has been isolated by genetic complementation of a faal mutant. This single copy gene, which maps to the right arm of chromosome XV, specifies a long chain acylCoA synthetase of 700 amino acids. Analyses of strains containing NMT1 and a faal null mutation indicated that FAA1 is not essential for vegetative growth when an active de novo pathway for fatty acid synthesis is present. The role of FAA1 in cellular lipid metabolism and protein N-myristoylation was therefore assessed in strains subjected to biochemical or genetic blockade of FAS. At 36 degrees C, FAA1 is required for the utilization of exogenous myristate by NMT and for the synthesis of several phospholipid species. This requirement is not apparent at 24 or 30 degrees C, suggesting that S. cerevisiae contains another acylCoA synthetase activity whose chain length and/or temperature optima may differ from Faalp.     

Regulation of acetyl-CoA synthetase of Saccharomyces cerevisiae.

Acetyl-coenzyme A synthetase (EC 6.2.1.1) activity of Saccharomyces cerevisiae was determined by a radioactive assay procedure. The activity in vitro was inhibited significantly by NADPH, NADH, or AMP and to a lesser extent by NADP, NAD, or ADP. Glutamic acid and alpha-ketoglutaric acid were not inhibitory. The enzyme level was repressed when the cells were grown in a complex nutrient medium as opposed to the minimal medium. However, a glutamic acid auxotroph glul, when grown in excess glutamic acid, demonstrated a fivefold increase of acetyl-CoA synthetase.     

Global mapping of protein phosphorylation events identifies Ste20, Sch9 and the cell-cycle regulatory kinases Cdc28/Pho85 as mediators of fatty acid starvation responses in Saccharomyces cerevisiae

Synthesis, degradation, and metabolism of fatty acids are strictly coordinated to meet the nutritional and energetic needs of cells and organisms. In the absence of exogenous fatty acids, proliferation and growth of the yeast Saccharomyces cerevisiae depends on endogenous synthesis of fatty acids, which is catalysed by fatty acid synthase. In the present study, we have used quantitative proteomics to examine the cellular response to inhibition of fatty acid synthesis in Saccharomyces cerevisiae. We have identified approximately 2000 phosphorylation sites of which more than 400 have been identified as being regulated in a temporal manner in response to inhibition of fatty acid synthesis by cerulenin. By bioinformatic analysis of these phosphorylation events, we have identified the cell cycle kinases Cdc28 and Pho85, the PAK kinase Ste20 as well as the protein kinase Sch9 as central mediators of the cellular response to inhibition of fatty acid synthesis.     

Temperature adaptation in yeasts: the role of fatty acids

Studies on the yeasts Candida oleophila, Candida utilis, Lipomyces starkeyi, Rhodosporidium toruloides and Saccharomyces cerevisiae revealed the existence of three different temperature adaptation responses involving changes in fatty acid composition. These conclusions were drawn by determining the growth rates, total cellular fatty acid content, fatty acid composition, degree of unsaturation, and the mean chain length of fatty acids over a range of growth temperatures. Within temperatures permitting growth, there were no changes in the major fatty acids of any of the yeasts, but the absolute amounts and relative compositions of the fatty acids did alter. In S. cerevisiae there were temperature-induced changes in the mean fatty acid chain length, whereas in R. toruloides there were changes in the degree of unsaturation. C. oleophila, C. utilis and L. starkeyi showed both responses, depending on whether the growth temperature was above or below 20-26 degrees C. Below 20-26 degrees C temperature-dependent changes were observed in the mean chain length whereas above 20-26 degrees C there were changes in the degree of unsaturation.     

Production of extracellular higher fatty acids by yeasts grown on hexadecanoic acid

Production of exocellular higher fatty acids by Candida yeasts was studied during their growth in a mineral medium with hexadecane. The qualitative and quantitative composition of exocellular higher fatty acids was investigated during cultivation of Candida lipolytica VCM Y 2378(695) under the conditions of different aeration (5 and 80% saturation of the medium with oxygen). Palmitic (C16:0), palmitooleic (C16:1), oleic (C18:1) and linoleic (C18:2) acids predominated among other higher fatty acids. The overall amount of fatty acids increased and the content of unsaturated fatty acids decreased when the yeast growth was limited with oxygen.