Construction and functional analysis of fatty acid desaturase gene disruptants in Candida albicans

Polyunsaturated fatty acids-enriched lipid from reduced sugar alcohol mannitol by marine yeast Rhodosporidiobolus fluvialis Y2

Brown macroalgae is a promising marine biomass for the production of bioethanol and biodiesel fuels. Here we investigate the biochemical processes used by marine oleaginous yeast for assimilating the major carbohydrate found in brown macroalgae. Briefly, yeast Rhodosporidiobolus fluvialis strain Y2 was isolated from seawater and grown in minimal medium containing reduced sugar alcohol mannitol as the sole carbon source with a salinity comparable to seawater. Conditions limiting nitrogen were used to facilitate lipid synthesis. R. fluvialis Y2 yielded 55.1% (w/w) and 39.1% (w/w) of lipids, per dry cell weight, from mannitol in the absence and presence of salinity, respectively. Furthermore, mannitol, as a sugar source, led to an increase in the composition of polyunsaturated fatty acids, linoleic acid (C18:2) and linolenic acid (C18:3), compared to glucose. This suggests that oxidation of mannitol leads to the activation of NADH-dependent fatty acid desaturases in R. fluvialis Y2. Such fatty acid composition may contribute to the cold-flow properties of biodiesel fuels. Our results identified a salt-tolerant oleaginous yeast species with unique metabolic traits, demonstrating a key role as a decomposer in the global carbon cycle through marine ecosystems. This is the first study on mannitol-induced synthesis of lipids enriched with polyunsaturated fatty acids by marine yeast.

Biotechnological potential of insect fatty acid-modifying enzymes

There are more than one million described insect species. This species richness is reflected in the diversity of insect metabolic processes. In particular, biosynthesis of secondary metabolites, such as defensive compounds and chemical signals, encompasses an extraordinarily wide range of chemicals that are generally unparalleled among natural products from other organisms. Insect genomes, transcriptomes and proteomes thus offer a valuable resource for discovery of novel enzymes with potential for biotechnological applications. Here, we focus on fatty acid (FA) metabolism-related enzymes, notably the fatty acyl desaturases and fatty acyl reductases involved in the biosynthesis of FA-derived pheromones. Research on insect pheromone-biosynthetic enzymes, which exhibit diverse enzymatic properties, has the potential to broaden the understanding of enzyme specificity determinants and contribute to engineering of enzymes with desired properties for biotechnological production of FA derivatives. Additionally, the application of such pheromone-biosynthetic enzymes represents an environmentally friendly and economic alternative to the chemical synthesis of pheromones that are used in insect pest management strategies.

Arabidopsis plants exposed to dioxin result in a WRINKLED seed phenotype due to 20S proteasomal degradation of WRI1

Dioxins are highly toxic persistent organic pollutants bioaccumulated by both plants and animals that cause severe developmental abnormalities in humans. We investigated the effects of dioxins on seed development in Arabidopsis. Plants were exposed to various concentrations of the most toxic congener of dioxins, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and the effects on seed development were analysed in-depth at transcriptome, proteome and metabolome levels. Exposure to dioxin led to generalized effects on vegetative tissues plus a specific set of perturbations to seed development. Mature seeds from TCDD-treated plants had a characteristic 'wrinkled' phenotype, due to a two-thirds reduction in storage oil content. Transcriptional analysis of a panel of genes related to lipid and carbohydrate metabolism was consistent with the observed biochemical phenotypes. There were increases in WRI1 and LEC1 expression but decreases in ABI3 and FUS3 expression, which is puzzling in view of the low seed oil phenotype. This anomaly was explained by increased expression of 20S proteasome components that resulted in a substantial degradation of WRI1 protein, despite the up-regulation of the WRI1 gene. Our findings reveal novel effects of dioxins that lead to altered gene regulation patterns that profoundly affect seed development in Arabidopsis.

Biogenic nanosilver synthesized in Metarhizium robertsii waste mycelium extract - As a modulator of Candida albicans morphogenesis, membrane lipidome and biofilm

Due to low efficacy of classic antimicrobial drugs, finding new active preparations attracts much attention. In this study an innovative, cost-effective and environmentally friendly method was applied to produce silver nanoparticles (AgNPs) using filamentous fungi Metarhizium robertsii biomass waste. It was shown that these NPs possess prominent antifungal effects against C. albicans, C. glabrata and C. parapsilosis reference strains. Further detailed studies were performed on C. albicans ATCC 90028. AgNPs kill curve (CFU method and esterase-mediated reduction of fluorescein diacetate); fractionally inhibitory concentration index (FICI) with fluconazole (FLC); effect on fungal cell membrane permeability (propidium iodide (PI) staining), membrane lipids profile (HPLC-MS), yeast morphotypes and intracellular reactive oxygen species level (H₂DCFDA probe) were investigated. Anti-adhesive and anti-biofilm properties of AgNPs (alone and in combination with FLC) were also tested. Biosafety of AgNPs use was assessed in vitro in cytotoxicity tests against L929 fibroblasts, pulmonary epithelial A549 cell line, and red blood cells. Significant reduction in the viability of yeast cells treated with AgNPs was shown within 6 h. The proportion of C. albicans PI-positive cells increased in a dose and time-dependent manner. Changes in the qualitative and quantitative profile of cell membrane lipids, including significant decline in the quantity of most phospholipid species containing C18:2 and an increase in the amount of phospholipids containing C18:1 acyl species were observed after yeast exposure to AgNPs. CLSM images showed an enhancement in ROS intracellular accumulation in C. albicans treated with biogenic nanosilver. C. albicans transformation from yeast to hyphal forms was also reduced. AgNPs decreased adhesion of yeast to abiotic surfaces, as well as acted synergistically with FLC against sessile population. At fungicidal and fungistatic concentrations, they were non-toxic to mammalian cells. Obtained results confirm suitability of our “green synthesis” method to produce AgNPs with therapeutic potential against fungal infections.

Candida albicans fatty acyl-CoA synthetase, CaFaa4p, is involved in the uptake of exogenous long-chain fatty acids and cell activity in the biofilm

Fatty acyl-CoA synthetase (Faa) activates fatty acid (FA) by converting the FA into the CoA ester in the cell. In the present study, we characterized a FAA homologue (CaFAA4) from the opportunistic pathogen Candida albicans. Most organisms can not only synthesize long-chain fatty acyl-CoAs (LCFA-CoAs) endogenously using a fatty acid synthase (Fas) activity but also can uptake long-chain fatty acids (LCFAs) from the extracellular environment and convert them into LCFA-CoAs via a vectorial acylation system. The budding yeast Saccharomyces cerevisiae possesses two LCFA-CoA synthetases, ScFaa1p and ScFaa4p. The disruption of ScFAA1 and ScFAA4 leads to synthetic lethality in the presence of a fatty acid synthesis inhibitor-cerulenin. The homologue-CaFAA4-rescued the lethality of an S. cerevisiae Scfaa1-Scfaa4 double mutant in the presence of cerulenin. On the other hand, a C. albicans faa4 mutant was unable to grow in the presence of cerulenin even if LCFAs were provided exogenously. Moreover, a biofilm analysis showed that the metabolic activity of the Cafaa4 mutant was approximately 40% lower than that of the wild-type parent, even though there was no significant difference in cell number or cell morphology between these strains. Notably, the Cafaa4 mutant showed increased susceptibility to micafungin during biofilm formation, a phenotype that presumably can be attributed to the impaired metabolism of the mutant strain. These results indicated that CaFaa4p is the unique C. albicans Faa protein responsible for activating LCFAs and is involved in the metabolism of biofilms.

Three, two, one yeast fatty acid desaturases: regulation and function

Fatty acid composition of biological membranes functionally adapts to environmental conditions by changing its composition through the activity of lipid biosynthetic enzymes, including the fatty acid desaturases. Three major desaturases are present in yeasts, responsible for the generation of double bonds in position C9-C10, C12-C13 and C15-C16 of the carbon backbone. In this review, we will report data addressed to define the functional role of basidiomycete and ascomycete yeast desaturase enzymes in response to various external signals and the regulation of the expression of their corresponding genes. Many yeast species have the complete set of three desaturases; however, only the Δ9 desaturase seems to be necessary and sufficient to ensure yeast viability. The evolutionary issue of this observation will be discussed.

Saccharomyces cerevisiae SHSY detoxifies petroleum n-alkanes by an induced CYP52A58 and an enhanced order in cell surface hydrophobicity

Environmental hydrocarbon contamination has a serious hazard to human health. Alkanes, the major component of hydrocarbons, can be consumed by various species of yeast. We previously identified a new strain SHSY of Saccharomyces cerevisiae with a remarkable ability to utilize the petroleum crude-oil (PCO) in aqueous solution. The current study demonstrated that the n-alkanes-assimilation activity of S. cerevisiae SHSY was related to an induced microsomal protein of 59 kDa approximately. The identified ORF encoded a protein of 517 amino acids and shared 93% sequence identity with an alkane-inducible hydroxylase CYP52A53 isolated from Scheffersomyces stipitis CBS. It was therefore referred as CYP52A58. The catalytic activity of the recombinant CYP52A58 was confirmed by the hydroxylation of n-alkanes, it showed an optimal mono-terminal hydroxylation activity toward n-hexadecane. Moreover, the ability of the yeast to use n-alkanes was accompanied with an increasing level in cell wall mannoproteins. Two differential protein bands were detected in the mannoproteins extracted from PCO-grown yeast. In parallel, a significant increase in the fatty acids content with a high degree of unsaturation was subsequently detected in the PCO-grown yeast. This study characterizes a safe and potential microorganism to remove n-alkanes from the aquatic environment.

Differential tissue accumulation of 2,3,7,8-Tetrachlorinated dibenzo-p-dioxin in Arabidopsis thaliana affects plant chronology, lipid metabolism and seed yield

BACKGROUND

Dioxins are one of the most toxic groups of persistent organic pollutants. Their biotransmission through the food chain constitutes a potential risk for human health. Plants as principal actors in the food chain can play a determinant role in removing dioxins from the environment. Due to the lack of data on dioxin/plant research, this study sets out to determine few responsive reactions adopted by Arabidopsis plant towards 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), the most toxic congener of dioxins.

RESULTS

Using a high resolution gas chromatography/mass spectrometry, we demonstrated that Arabidopsis plant uptakes TCDD by the roots and accumulates it in the vegetative parts in a tissue-specific manner. TCDD mainly accumulated in rosette leaves and mature seeds and less in stem, flowers and immature siliques. Moreover, we observed that plants exposed to high doses of TCDD exhibited a delay in flowering and yielded fewer seeds of a reduced oil content with a low vitality. A particular focus on the plant fatty acid metabolism showed that TCDD caused a significant reduction in C18-unsaturated fatty acid level in plant tissues. Simultaneously, TCDD induced the expression of 9-LOX and 13-LOX genes and the formation of their corresponding hydroperoxides, 9- and 13-HPOD as well as 9- or 13-HPOT, derived from linoleic and linolenic acids, respectively.

CONCLUSIONS

The current work highlights a side of toxicological effects resulting in the administration of 2,3,7,8-TCDD on the Arabidopsis plant. Similarly to animals, it seems that plants may accumulate TCDD in their lipids by involving few of the FA-metabolizing enzymes for sculpting a specific oxylipins "signature" typified to plant TCDD-tolerance. Together, our results uncover novel responses of Arabidopsis to dioxin, possibly emerging to overcome its toxicity.

Δ12-Fatty acid desaturase from Candida parapsilosis is a multifunctional desaturase producing a range of polyunsaturated and hydroxylated fatty acids

Numerous Δ12-, Δ15- and multifunctional membrane fatty acid desaturases (FADs) have been identified in fungi, revealing great variability in the enzymatic specificities of FADs involved in biosynthesis of polyunsaturated fatty acids (PUFAs). Here, we report gene isolation and characterization of novel Δ12/Δ15- and Δ15-FADs named CpFad2 and CpFad3, respectively, from the opportunistic pathogenic yeast Candida parapsilosis. Overexpression of CpFad3 in Saccharomyces cerevisiae strains supplemented with linoleic acid (Δ9,Δ12-18:2) and hexadecadienoic acid (Δ9,Δ12-16:2) leads to accumulation of Δ15-PUFAs, i.e., α-linolenic acid (Δ9,Δ12,Δ15-18:3) and hexadecatrienoic acid with an unusual terminal double bond (Δ9,Δ12,Δ15-16:3). CpFad2 produces a range of Δ12- and Δ15-PUFAs. The major products of CpFad2 are linoleic and hexadecadienoic acid (Δ9,Δ12-16:2), accompanied by α-linolenic acid and hexadecatrienoic acid (Δ9,Δ12,Δ15-16:3). Using GC/MS analysis of trimethylsilyl derivatives, we identified ricinoleic acid (12-hydroxy-9-octadecenoic acid) as an additional product of CpFad2. These results demonstrate that CpFAD2 is a multifunctional FAD and indicate that detailed analysis of fatty acid derivatives might uncover a range of enzymatic selectivities in other Δ12-FADs from budding yeasts (Ascomycota: Saccharomycotina).

Characterization of a lysophospholipid acyltransferase involved in membrane remodeling in Candida albicans

Phospholipid remodeling involves phospholipase activity to remove acyl chains and acyltransferases to replace acyl chains. We here describe the characterization of a lysophospholipid acyltransferase in the opportunistic fungal pathogen, Candida albicans. Expression of this gene, C.a. LPT1, complemented the lysophospholipid acyltransferase defect in Saccharomyces cerevisiae strains lacking the homologous LPT1 gene. In vitro, lysophospholipid acyltransferase activity in these strains showed acyl-CoA substrate specificity, as measured by apparent Vmax/Km ratios, to be linolenoyl-CoA>oleoyl-CoA>linoleoyl-CoA>stearoyl-CoA. To address the physiological importance of C.a. LPT1, homozygous deletion strains were generated. Lysophospholipid acyltransferase activity with amine containing lysophospholipids was dramatically reduced while lysophosphatidylinositol and lysophosphatidic acid esterification was not significantly lowered. However, C.a. LPT1 over-expression yielded an increased amount of lysophosphatidic acyltransferase activity, suggesting a role in de novo phospholipid synthesis. LPT1 deletion strains showed slightly slowed growth in standard liquid media but no phenotype in media containing three antifungals that target sterols. To assess the role of C.a. Lpt1 in phospholipid remodeling, an in vivo, pulse-chase assay utilizing polysorbitan palmitate and mass spectrometry was developed. Cellular phospholipid composition became atypical with the provision of palmitate and gradually returned to the typical distribution when palmitate was removed. Deletion of C.a. LPT1 showed a modest yet significant effect on remodeling under these conditions.

Effect of Edible Sesame Oil on Growth of Clinical Isolates of Candida albicans

Elderly individuals are at increased risk of oral thrush (oral candidiasis) due to decreased saliva secretion. Due to their antimicrobial properties, edible oils can be effective natural agents for oral care. The objective of the present study was to compare the effects of sesame oil, which is widely used for cooking in Asian countries, and two other edible oils on the growth of both mycelial and yeast forms of five clinical isolates of Candida albicans, a causative microorganism of oral thrush. We assessed the effect of each oil in concentrations of 0.078%, 0.156%, and 0.313% on growth of the mycelial forms of the clinical isolates over 24 hr using the crystal violet method. We also evaluated the effect of each oil on growth of the yeast forms by counting the number of viable yeast cells after culturing in the oils for 24 hr. Sesame oil inhibited the growth of both mycelial and yeast forms. Safflower and olive oil also inhibited the growth of both forms of C. albicans but to a lesser extent than sesame oil. The ability to inhibit the growth of the mycelial form correlated with sesame oil concentration. Roasting influenced growth inhibition ability and high-roasted sesame oil most effectively inhibited the yeast form. The growth inhibitory effect differed among the five isolates. We hypothesize that the sesamin and fatty acid components of sesame oil are involved in its antifungal activity.

Knockout of fatty acid desaturase genes in Pichia pastoris GS115 and its effect on the fatty acid biosynthesis and physiological consequences

Unsaturated fatty acids (UFAs), including oleic acid (OA, C18:1n-9), linoleic acid (LA, C18:2n-6) and α-linolenic acid (ALA, C18:3n-3), are major components of membrane lipids in Pichia pastoris GS115. In order to clarify the biosynthesis pathway of UFAs on the molecular level and investigate their possible roles in growth and development of this strain, we here report modified strains with disrupted desaturase gene by homologous recombination. Gas chromatography analysis of fatty acid composition in the corresponding mutants confirmed that ∆(12)-desaturase encoded by Fad12 was responsible for the formation of LA, and ALA was synthesized by ∆(15)-desaturase encoded by Fad15. Simultaneous deletion of Fad9A and Fad9B was lethal and supplementation of OA could restore growth, indicating that possibly both Fad9A and Fad9B encoded ∆(9)-desaturase that converted SA into OA. Phenotypic analysis demonstrated that wild type and Fad15 mutant grew at almost the same rate, Fad12 mutant grew much slower than these two strains. Moreover, OA was positively correlated to cold tolerance and ethanol tolerance of GS115, whereas LA and ALA did not affect cold tolerance and ethanol tolerance of it. In addition, we showed that tolerance of GS115 to high concentration of methanol was independent of these three UFAs.

The stearoyl-coenzyme A desaturase 1 is essential for virulence and membrane stress in Candida parapsilosis through unsaturated fatty acid production

Unsaturated fatty acids (UFA) are essential components of cells. In Saccharomyces cerevisiae, stearoyl-coenzyme A (CoA) desaturase 1 (OLE1) affects cell viability through the regulation of oleic (18:1) or palmitoleic (16:1) acid production. In this study, we used a targeted gene deletion approach to determine the impact of OLE1 on the emerging human pathogenic fungus Candida parapsilosis. We found that the deletion of OLE1 resulted in an auxotrophic yeast strain (designated OLE1 KO) that required unsaturated fatty acids for growth but not saturated fatty acids. Additionally, the production of UFA by OLE1 KO yeast cells was markedly reduced, suggesting that Ole1 is essential for UFA production. In contrast to wild-type C. parapsilosis, which produced pseudohyphal growth on UFA-supplemented medium agar, pseudohyphal formation in the OLE1 KO cells was severely impaired, suggesting that Ole1 regulates morphology. Furthermore, the OLE1 KO cells were hypersensitive to various stress-inducing factors, such as salts, SDS, and H(2)O(2), especially at the physiological temperature. The results indicate that OLE1 is essential for the stress response, perhaps through the production of UFA for cell membrane biosynthesis. The OLE1 KO cells also were hypersensitive to human and fetal bovine serum, suggesting that targeting Ole1 could suppress the dissemination of yeast cells in the bloodstream. Murine-like macrophage J774.16 more efficiently killed the OLE1 KO yeasts, and significantly larger amounts of nitric oxide were detected in cocultures of macrophages and OLE1 KO cells than with wild-type or heterozygous strains. Moreover, the disruption of OLE1 significantly reduced fungal virulence in systemic murine infection. Taken together, these results demonstrate that Ole1 regulates the pathobiology of C. parapsilosis via UFA and that the OLE1 pathway is a promising antifungal target.

Major impacts on the primary metabolism of the plant pathogen Cryphonectria parasitica by the virulence-attenuating virus CHV1-EP713

Cryphonectria parasitica, the chestnut blight fungus, can be infected by virulence-attenuating mycoviruses of the family Hypoviridae. Previous studies have led to the hypothesis that the hypovirus-infected phenotype is partly due to metabolic changes induced by the viral infection. To investigate this, we measured the metabolic rate and respiration of C. parasitica colonies grown on solid medium. These experiments supported historical observations of other fungal species done in liquid cultures that the metabolic rate steadily declines with age and differentiation of the mycelium. Hypovirus infection increased metabolic rate in the youngest mycelium, but a subsequent decline was also observed as the mycelium aged. By measuring both CO(2) production and O(2) consumption, we also observed that changes occur in carbohydrate metabolism as a result of ageing in both infected and uninfected mycelium. Mycelium on the periphery of the colony exploited fermentation pathways extensively, before transitioning to aerobic carbohydrate metabolism and finally lipid metabolism in the interior regions, despite abundant remaining glucose. However, the hypovirus affected the extent of these changes, with infected mycelium apparently unable to utilize lipid-related metabolic pathways, leading to an increased depletion of glucose. Finally, we used metabolic profi fi ling to determine the changes in accumulation of primary metabolites in wild-type and hypovirus-infected mycelium and found that approximately one-third of the 164 detected metabolites were affected. These results are consistent with those expected from the physiological measurements, with significant alterations noted for compounds related to lipid and carbohydrate metabolism. Additionally, we observed an increase in the accumulation of the polyamine spermidine in the presence of hypovirus. Polyamines have been implicated in antiviral responses of mammalian systems; therefore this may suggest a novel antiviral response mechanism in fungi.

Chemical genetic profiling and characterization of small-molecule compounds that affect the biosynthesis of unsaturated fatty acids in Candida albicans

The balance between saturated and unsaturated fatty acids plays a crucial role in determining the membrane fluidity. In the diploid fungal pathogen Candida albicans, the gene for fatty acid Delta9 desaturase, OLE1, is essential for viability. Using a reverse genetic approach, termed the fitness test, we identified a group of structurally related synthetic compounds that induce specific hypersensitivity of the OLE1(+/-) strain. Genetic repression of OLE1 and chemical inhibition by two selected compounds, ECC145 and ECC188, resulted in a marked decrease in the total unsaturated fatty acids and impaired hyphal development. The resulting auxotroph of both was suppressed by the exogenous monounsaturated fatty acids (16:1Delta9 and 18:1Delta9). These correlations suggest that both compounds affect the level of unsaturated fatty acids, likely by impairing Ole1p directly or indirectly. However, the residual levels of monounsaturated fatty acids (MUFAs) resulted from chemical inhibition were significantly higher than OLE1 repression, indicating even partial inhibition of MUFAs is sufficient to stop cellular proliferation. Although the essentiality of OLE1 was suppressed by MUFAs in vitro, we demonstrated that it was required for virulence in a murine model of systemic candidiasis even when the animals were supplemented with a high fat diet. Thus, the fungal fatty acid desaturase is an attractive antifungal drug target. Taking advantage of the inhibitors and the relevant conditional shut-off strains, we validated several chemical genetic interactions observed in the fitness test profiles that reveal novel genetic interactions between OLE1/unsaturated fatty acids and other cellular processes.

Depletion of the cullin Cdc53p induces morphogenetic changes in Candida albicans

Candida albicans is an important opportunistic human fungal pathogen that can cause both mucosal and systemic infections in immunocompromised patients. Critical for the virulence of C. albicans is its ability to undergo a morphological transition from yeast to hyphal growth mode. Proper induction of filamentation is dependent on the ubiquitination pathway, which targets proteins for proteasome-mediated protein degradation or activates them for signaling events. In the present study, we evaluated the role of ubiquitination in C. albicans by impairing the function of the major ubiquitin-ligase complex SCF. This was done by depleting its backbone, the cullin Cdc53p (orf19.1674), using a tetracycline downregulatable promoter system. Cdc53p-depleted cells displayed an invasive phenotype and constitutive filamentation under conditions favoring yeast growth mode, both on solid and in liquid media. In addition, these cells exhibited an early onset of cell death, as judged from propidium iodide staining, suggesting that CDC53 is an essential gene in C. albicans. To identify Cdc53p-dependent pathways in C. albicans, a genome-wide expression analysis was carried out that revealed a total of 425 differentially expressed genes (fold change, >or=2; P <or= 0.05) with 192 up- and 233 downregulated genes in the CDC53-repressed mutant compared to the control strain. GO term analysis identified biological processes significantly affected by Cdc53p depletion, including amino acid starvation response, with 14 genes being targets of the transcriptional regulator Gcn4p, and reductive iron transport. These results indicate that Cdc53p enables C. albicans to adequately respond to environmental signals.

Transcriptional Response of Candida albicans to Hypoxia: Linkage of Oxygen Sensing and Efg1p-regulatory Networks

The major human fungal pathogen, Candida albicans, colonizes different body sites, differing greatly in oxygen levels. Using whole-genome DNA microarrays, we analysed the transcriptomal response of C. albicans to hypoxia. In this condition, transcripts of genes involved in fermentative metabolism, including glycolytic genes, as well as hypha-specific genes, were up-regulated; in contrast, genes regulating oxidative metabolism were down-regulated. Although the morphogenetic and metabolic regulator Efg1p regulates these genes during normoxia, we found that Efg1p is not involved in their hypoxic regulation. Instead, Efg1p was specifically required for hypoxic expression or repression of subsets of genes. One class of hypoxia-regulated genes, encoding proteins involved in fatty acid biosynthesis, was dependent on Efg1p for maximal hypoxic expression, requiring Efg1p for transcriptional activation. During hypoxia, efg1 mutants contained lower levels of unsaturated fatty acids, while hyphal morphogenesis on solid media was significantly increased at temperatures <37 degrees C. These results suggest that during oxygen-limitation, Efg1p acts as a repressor of filamentation and as a positive regulator of fatty acid desaturation. We discuss that C. albicans responds to hypoxia largely by different mechanisms compared to budding yeast and that hypoxic adaptation requiring Efg1p is crucial for successful infection of human cells and tissues.