Deletion of the ATH1 gene in Saccharomyces cerevisiae prevents growth on trehalose

Metatranscriptomics reveals diversity of symbiotic interaction and mechanisms of carbon exchange in the marine cyanolichen Lichina pygmaea

Lichens are exemplar symbioses based upon carbon exchange between photobionts and their mycobiont hosts. Historically considered a two-way relationship, some lichen symbioses have been shown to contain multiple photobiont partners; however, the way in which these photobiont communities react to environmental change is poorly understood. Lichina pygmaea is a marine cyanolichen that inhabits rocky seashores where it is submerged in seawater during every tidal cycle. Recent work has indicated that L. pygmaea has a complex photobiont community including the cyanobionts Rivularia and Pleurocapsa. We performed rRNA-based metabarcoding and mRNA metatranscriptomics of the L. pygmaea holobiont at high and low tide to investigate community response to immersion in seawater. Carbon exchange in L. pygmaea is a dynamic process, influenced by both tidal cycle and the biology of the individual symbiotic components. The mycobiont and two cyanobiont partners exhibit distinct transcriptional responses to seawater hydration. Sugar-based compatible solutes produced by Rivularia and Pleurocapsa in response to seawater are a potential source of carbon to the mycobiont. We propose that extracellular processing of photobiont-derived polysaccharides is a fundamental step in carbon acquisition by L. pygmaea and is analogous to uptake of plant-derived carbon in ectomycorrhizal symbioses.

Improving the productivity of malic acid by alleviating oxidative stress during Aspergillus niger fermentation

BACKGROUND

As an attractive platform chemical, malic acid has been commonly used in the food, feed and pharmaceutical field. Microbial fermentation of biobased sources to produce malic acid has attracted great attention because it is sustainable and environment-friendly. However, most studies mainly focus on improving yield and ignore shortening fermentation time. A long fermentation period means high cost, and hinders the industrial applications of microbial fermentation. Stresses, especially oxidative stress generated during fermentation, inhibit microbial growth and production, and prolong fermentation period. Previous studies have shown that polypeptides could effectively relieve stresses, but the underlying mechanisms were poorly understood.

RESULTS

In this study, polypeptides (especially elastin peptide) addition improves the productivity of malic acid in A. niger, resulting in shortening of fermentation time from 120 to 108 h. Transcriptome and biochemical analyses demonstrated that both antioxidant enzyme-mediated oxidative stress defense system, such as superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPX), and nonenzymatic antioxidant system, such as glutathione, were enhanced in the presence of elastin peptide, suggesting elastin peptide relieving oxidative stresses is involved in many pathways. In order to further investigate the relationship between oxidative stress defense and malic acid productivity, we overexpressed three enzymes (Sod1, CAT, Tps1) related to oxidation resistance in A. niger, respectively, and these resulting strains display varying degree of improvement in malic acid productivity. Especially, the strain overexpressing the Sod1 gene achieved a malate titer of 91.85 ± 2.58 g/L in 96 h, corresponding to a productivity of 0.96 g/L/h, which performs better than elastin peptide addition.

CONCLUSIONS

Our investigation provides an excellent reference for alleviating the stress of the fungal fermentation process and improving fermentation efficiency.

The involvement of the Candida glabrata trehalase enzymes in stress resistance and gut colonization

Candida glabrata is an opportunistic human fungal pathogen and is frequently present in the human microbiome. It has a high relative resistance to environmental stresses and several antifungal drugs. An important component involved in microbial stress tolerance is trehalose. In this work, we characterized the three C. glabrata trehalase enzymes Ath1, Nth1 and Nth2. Single, double and triple deletion strains were constructed and characterized both in vitro and in vivo to determine the role of these enzymes in virulence. Ath1 was found to be located in the periplasm and was essential for growth on trehalose as sole carbon source, while Nth1 on the other hand was important for oxidative stress resistance, an observation which was consistent by the lower survival rate of the NTH1 deletion strain in human macrophages. No significant phenotype was observed for Nth2. The triple deletion strain was unable to establish a stable colonization of the gastrointestinal (GI) tract in mice indicating the importance of having trehalase activity for colonization in the gut.

The Inhibitory Effect of Validamycin A on Aspergillus flavus

Aspergillus flavus is one of the most common isolates from patients with fungal infections. Aspergillus infection is usually treated with antifungal agents, but side effects of these agents are common. Trehalase is an essential enzyme involved in fungal metabolism, and the trehalase inhibitor, validamycin A, has been used to prevent fungal infections in agricultural products. In this study, we observed that validamycin A significantly increased trehalose levels in A. flavus conidia and delayed germination, including decreased fungal adherence. In addition, validamycin A and amphotericin B showed a combinatorial effect on A. flavus ATCC204304 and clinical isolates with high minimum inhibitory concentrations (MICs) of amphotericin B using checkerboard assays. We observed that validamycin A and amphotericin B had a synergistic effect on A. flavus strains resistant to amphotericin B. The MICs in the combination of validamycin A and amphotericin B were at 0.125 μg/mL and 2 μg/mL, respectively. The FICI of validamycin A and amphotericin B of these clinical isolates was about 0.25-0.28 with synergistic effects. No drug cytotoxicity was observed in human bronchial epithelial cells treated with validamycin A using LDH-cytotoxicity assays. In conclusion, this study demonstrated that validamycin A inhibited the growth of A. flavus and delayed conidial germination. Furthermore, the combined effect of validamycin A with amphotericin B increased A. flavus killing, without significant cytotoxicity to human bronchial epithelial cells. We propose that validamycin A could potentially be used in vivo as an alternative treatment for A. flavus infections.

Deletion of the trehalose tps1 gene in Kluyveromyces lactis does not impair growth in glucose

Trehalose is a non-reducing disaccharide composed of two α-glucose molecules and synthesized by an enzyme complex containing four subunits TPS1 (EC 2.4.1.15), TPS2 (EC 3.1.3.12), TPS3 and TSL1. First reports about trehalose classified this sugar as an energy reserve compound like glycogen. However, lately, trehalose is known to assist yeast cells during heat, osmotic and starvation stresses. In Saccharomyces cerevisiae, the deletion of the tps1 encoding gene eliminated the yeast ability to grow on glucose as the sole carbon source. Kluyveromyces lactis is a yeast present in various dairy products and is currently utilized for the synthesis of more than 40 industrial heterologous products. In this study, the deletion of the tps1 gene in K. lactis showed that unlike S. cerevisiae, tps1 gene disruption does not cause growth failure in glucose, galactose, or fructose. The µMAX rate values of K. lactis tps1Δ strains were equal than the non-disrupted strains, showing that the gene deletion does not affect the yeast growth. After gene disruption, the absence of trehalose into the metabolism of K. lactis was also confirmed.

Diverse and common features of trehalases and their contributions to microbial trehalose metabolism

Trehalose is a stable disaccharide that consists of two glucose units linked primarily by an α,α-(1 → 1)-linkage, and it has been found in a wide variety of organisms. In these organisms, trehalose functions not only as a source of carbon energy but also as a protector against various stress conditions. In addition, this disaccharide is attractive for use in a wide range of applications due to its bioactivities. In trehalose metabolism, direct trehalose-hydrolyzing enzymes are known as trehalases, which have been reported for bacteria, archaea, and eukaryotes, and are classified into glycoside hydrolase 37 (GH37), GH65, and GH15 families according to the Carbohydrate-Active enZyme (CAZy) database. The catalytic domains (CDs) of these enzymes commonly share (α/α)₆-barrel structures and have two amino acid residues, Asp and/or Glu, that function as catalytic residues in an inverting mechanism. In this review, I focus on diverse and common features of trehalases within different GH families and their contributions to microbial trehalose metabolism.

Vacuolar hydrolysis and efflux: current knowledge and unanswered questions

Hydrolysis within the vacuole in yeast and the lysosome in mammals is required for the degradation and recycling of a multitude of substrates, many of which are delivered to the vacuole/lysosome by autophagy. In humans, defects in lysosomal hydrolysis and efflux can have devastating consequences, and contribute to a class of diseases referred to as lysosomal storage disorders. Despite the importance of these processes, many of the proteins and regulatory mechanisms involved in hydrolysis and efflux are poorly understood. In this review, we describe our current knowledge of the vacuolar/lysosomal degradation and efflux of a vast array of substrates, focusing primarily on what is known in the yeast Saccharomyces cerevisiae. We also highlight many unanswered questions, the answers to which may lead to new advances in the treatment of lysosomal storage disorders. Abbreviations: Ams1: α-mannosidase; Ape1: aminopeptidase I; Ape3: aminopeptidase Y; Ape4: aspartyl aminopeptidase; Atg: autophagy related; Cps1: carboxypeptidase S; CTNS: cystinosin, lysosomal cystine transporter; CTSA: cathepsin A; CTSD: cathepsin D; Cvt: cytoplasm-to-vacuole targeting; Dap2: dipeptidyl aminopeptidase B; GS-bimane: glutathione-S-bimane; GSH: glutathione; LDs: lipid droplets; MVB: multivesicular body; PAS: phagophore assembly site; Pep4: proteinase A; PolyP: polyphosphate; Prb1: proteinase B; Prc1: carboxypeptidase Y; V-ATPase: vacuolar-type proton-translocating ATPase; VTC: vacuolar transporter chaperone.

Gene expression related to trehalose metabolism and its effect on Volvariella volvacea under low temperature stress

The mechanism of the low temperature autolysis of Volvariella volvacea (V. volvacea) has not been thoroughly explained, and trehalose is one of the most important osmolytes in the resistance of fungi to adversity. The present study used the low temperature sensitive V. volvacea strain V23 and the low temperature tolerant strain VH3 as test materials. Intracellular trehalose contents under low temperature stress in the two strains were measured by high performance liquid chromatography (HPLC). Quantitative real-time PCR (qPCR) analysis was carried out to study the transcriptional expression differences of enzymes related to trehalose metabolism. And trehalose solution was exogenously added during the cultivation of fruit bodies of V. volvacea. The effect of exogenous trehalose solution on the anti-hypothermia of fruit bodies was studied by evaluating the sensory changes under low temperature storage after harvest. The results showed that the intracellular trehalose content in VH3 was higher than that in V23 under low temperature stress. In the first 2 h of low temperature stress, the expression of trehalose-6-phosphate phosphatase (TPP) gene involved in trehalose synthesis decreased, while the expression of trehalose phosphorylase (TP) gene increased. The expression of TPP gene was almost unchanged in VH3, but it decreased dramatically in V23 at 4 h of low temperature stress. The expression levels of TPP and TP genes in VH3 was significantly higher than that in V23 from 6 h to 8 h of low temperature stress. TP gene may be a crucial gene of trehalose metabolism, which was more inclined to synthesize trehalose during low temperature stress. In addition, the sensory traits of V. volvacea fruit bodies stored at 4 °C were significantly improved by the application of exogenous trehalose compared with the controls. Thus, trehalose could help V. volvacea in response to low temperature stress and high content of it may be one of the reasons that why VH3 strain was more tolerant to the low temperature stress than V23 strain.

Central Role of the Trehalose Biosynthesis Pathway in the Pathogenesis of Human Fungal Infections: Opportunities and Challenges for Therapeutic Development

Invasive fungal infections cause significant morbidity and mortality in part due to a limited antifungal drug arsenal. One therapeutic challenge faced by clinicians is the significant host toxicity associated with antifungal drugs. Another challenge is the fungistatic mechanism of action of some drugs. Consequently, the identification of fungus-specific drug targets essential for fitness in vivo remains a significant goal of medical mycology research. The trehalose biosynthetic pathway is found in a wide variety of organisms, including human-pathogenic fungi, but not in humans. Genes encoding proteins involved in trehalose biosynthesis are mechanistically linked to the metabolism, cell wall homeostasis, stress responses, and virulence of Candida albicans, Cryptococcus neoformans, and Aspergillus fumigatus. While there are a number of pathways for trehalose production across the tree of life, the TPS/TPP (trehalose-6-phosphate synthase/trehalose-6-phosphate phosphatase) pathway is the canonical pathway found in human-pathogenic fungi. Importantly, data suggest that proteins involved in trehalose biosynthesis play other critical roles in fungal metabolism and in vivo fitness that remain to be fully elucidated. By further defining the biology and functions of trehalose and its biosynthetic pathway components in pathogenic fungi, an opportunity exists to leverage this pathway as a potent antifungal drug target. The goal of this review is to cover the known roles of this important molecule and its associated biosynthesis-encoding genes in the human-pathogenic fungi studied to date and to employ these data to critically assess the opportunities and challenges facing development of this pathway as a therapeutic target.

Changes of trehalose content and expression of relative genes during the bioethanol fermentation by Saccharomyces cerevisiae

Traditionally, trehalose is considered as a protectant to improve the ethanol tolerance of Saccharomyces cerevisiae. In this study, to clarify the changes and roles of trehalose during the bioethanol fermentation, trehalose content and expression of related genes at lag, exponential, and stationary phases (i.e., 2, 8, and 16 h of batch fermentation process) were determined. Although yeast cells at exponential and stationary phase had higher trehalose content than cells at lag phase (P < 0.01), there was no significant difference in trehalose content between exponential and stationary phases (P > 0.05). Moreover, expression of the trehalose degradation-related genes NTH1 and NTH2 decreased at exponential phase in comparison with that at lag phase; compared with cells at lag phase, cells at stationary phase had higher expression of TPS1, ATH1, NTH1, and NTH2 but lower expression of TPS2. During the lag-exponential phase transition, downregulation of NTH1 and NTH2 promoted accumulation of trehalose, and to some extent, trehalose might confer ethanol tolerance to S. cerevisiae before stationary phase. During the exponential-stationary phase transition, upregulation of TPS1 contributed to accumulation of trehalose, and Tps1 protein might be indispensable in yeast cells to withstand ethanol stress at the stationary phase. Moreover, trehalose would be degraded to supply carbon source at stationary phase.

Genome analysis of Daldinia eschscholtzii strains UM 1400 and UM 1020, wood-decaying fungi isolated from human hosts

BACKGROUND

Daldinia eschscholtzii is a wood-inhabiting fungus that causes wood decay under certain conditions. It has a broad host range and produces a large repertoire of potentially bioactive compounds. However, there is no extensive genome analysis on this fungal species.

RESULTS

Two fungal isolates (UM 1400 and UM 1020) from human specimens were identified as Daldinia eschscholtzii by morphological features and ITS-based phylogenetic analysis. Both genomes were similar in size with 10,822 predicted genes in UM 1400 (35.8 Mb) and 11,120 predicted genes in UM 1020 (35.5 Mb). A total of 751 gene families were shared among both UM isolates, including gene families associated with fungus-host interactions. In the CAZyme comparative analysis, both genomes were found to contain arrays of CAZyme related to plant cell wall degradation. Genes encoding secreted peptidases were found in the genomes, which encode for the peptidases involved in the degradation of structural proteins in plant cell wall. In addition, arrays of secondary metabolite backbone genes were identified in both genomes, indicating of their potential to produce bioactive secondary metabolites. Both genomes also contained an abundance of gene encoding signaling components, with three proposed MAPK cascades involved in cell wall integrity, osmoregulation, and mating/filamentation. Besides genomic evidence for degrading capability, both isolates also harbored an array of genes encoding stress response proteins that are potentially significant for adaptation to living in the hostile environments.

CONCLUSIONS

Our genomic studies provide further information for the biological understanding of the D. eschscholtzii and suggest that these wood-decaying fungi are also equipped for adaptation to adverse environments in the human host.

Secretion of the acid trehalase encoded by the CgATH1 gene allows trehalose fermentation by Candida glabrata

The emergent pathogen Candida glabrata differs from other yeasts because it assimilates only two sugars, glucose and the disaccharide trehalose. Since rapid identification tests are based on the ability of this yeast to rapidly hydrolyze trehalose, in this work a biochemical and molecular characterization of trehalose catabolism by this yeast was performed. Our results show that C. glabrata consumes and ferments trehalose, with parameters similar to those observed during glucose fermentation. The presence of glucose in the medium during exponential growth on trehalose revealed extracellular hydrolysis of the sugar by a cell surface acid trehalase with a pH optimum of 4.4. Approximately ∼30% of the total enzymatic activity is secreted into the medium during growth on trehalose or glycerol. The secreted enzyme shows an apparent molecular mass of 275 kDa in its native form, but denaturant gel electrophoresis revealed a protein with ∼130 kDa, which due to its migration pattern and strong binding to concanavalin A, indicates that it is probably a dimeric glycoprotein. The secreted acid trehalase shows high affinity and activity for trehalose, with Km and Vmax values of 3.4 mM and 80 U (mg protein)(-1), respectively. Cloning of the CgATH1 gene (CAGLOK05137g) from de C. glabrata genome, a gene showing high homology to fungal acid trehalases, allowed trehalose fermentation after heterologous expression in Saccharomyces cerevisiae.

Characterizing the in vivo role of trehalose in Saccharomyces cerevisiae using the AGT1 transporter

Trehalose is a highly stable, nonreducing disaccharide of glucose. A large body of research exists implicating trehalose in a variety of cellular phenomena, notably response to stresses of various kinds. However, in very few cases has the role of trehalose been examined directly in vivo. Here, we describe the development and characterization of a system in Saccharomyces cerevisiae that allows us to manipulate intracellular trehalose concentrations independently of the biosynthetic enzymes and independently of any applied stress. We found that many physiological roles heretofore ascribed to intracellular trehalose, including heat resistance, are not due to the presence of trehalose per se. We also found that many of the metabolic and growth defects associated with mutations in the trehalose biosynthesis pathway are not abolished by providing abundant intracellular trehalose. Instead, we made the observation that intracellular accumulation of trehalose or maltose (another disaccharide of glucose) is growth-inhibitory in a carbon source-specific manner. We conclude that the physiological role of the trehalose pathway is fundamentally metabolic: i.e., more complex than simply the consequence of increased concentrations of the sugar and its attendant physical properties (with the exception of the companion paper where Tapia et al. [Tapia H, et al. (2015) Proc Natl Acad Sci USA, 10.1073/pnas.1506415112] demonstrate a direct role for trehalose in protecting cells against desiccation).

Enhanced freeze tolerance of baker’s yeast by overexpressed trehalose-6-phosphate synthase gene (TPS1) and deleted trehalase genes in frozen dough

Several recombinant strains with overexpressed trehalose-6-phosphate synthase gene (TPS1) and/or deleted trehalase genes were obtained to elucidate the relationships between TPS1, trehalase genes, content of intracellular trehalose and freeze tolerance of baker’s yeast, as well as improve the fermentation properties of lean dough after freezing. In this study, strain TL301TPS1 overexpressing TPS1 showed 62.92 % higher trehalose-6-phosphate synthase (Tps1) activity and enhanced the content of intracellular trehalose than the parental strain. Deleting ATH1 exerted a significant effect on trehalase activities and the degradation amount of intracellular trehalose during the first 30 min of prefermentation. This finding indicates that acid trehalase (Ath1) plays a role in intracellular trehalose degradation. NTH2 encodes a functional neutral trehalase (Nth2) that was significantly involved in intracellular trehalose degradation in the absence of the NTH1 and/or ATH1 gene. The survival ratio, freeze-tolerance ratio and relative fermentation ability of strain TL301TPS1 were approximately twice as high as those of the parental strain (BY6-9α). The increase in freeze tolerance of strain TL301TPS1 was accompanied by relatively low trehalase activity, high Tps1 activity and high residual content of intracellular trehalose. Our results suggest that overexpressing TPS1 and deleting trehalase genes are sufficient to improve the freeze tolerance of baker’s yeast in frozen dough. The present study provides guidance for the commercial baking industry as well as the research on the intracellular trehalose mobilization and freeze tolerance of baker’s yeast.

In Candida parapsilosis the ATC1 gene encodes for an acid trehalase involved in trehalose hydrolysis, stress resistance and virulence

An ORF named CPAR2-208980 on contig 005809 was identified by screening a Candida parapsilosis genome data base. Its 67% identity with the acid trehalase sequence from C. albicans (ATC1) led us to designate it CpATC1. Homozygous mutants that lack acid trehalase activity were constructed by gene disruption at the two CpATC1 chromosomal alleles. Phenotypic characterization showed that atc1Δ null cells were unable to grow on exogenous trehalose as carbon source, and also displayed higher resistance to environmental challenges, such as saline exposure (1.2 M NaCl), heat shock (42°C) and both mild and severe oxidative stress (5 and 50 mM H2O2). Significant amounts of intracellular trehalose were specifically stored in response to the thermal upshift in both wild type and mutant strains. Analysis of their antioxidant activities revealed that catalase was only triggered in response to heat shock in atc1Δ cells, whereas glutathione reductase was activated upon mild oxidative stress in wild type and reintegrant strains, and in response to the whole set of stress treatments in the homozygous mutant. Furthermore, yeast cells with double CpATC1 deletion were significantly attenuated in non-mammalian infection models, suggesting that CpATC1 is required for the pathobiology of the fungus. Our results demonstrate the involvement of CpAtc1 protein in the physiological hydrolysis of external trehalose in C. parapsilosis, where it also plays a major role in stress resistance and virulence.

Improvements of tolerance to stress conditions by genetic engineering in Saccharomyces cerevisiae during ethanol production

Saccharomyces cerevisiae, industrial yeast isolate, has been of great interest in recent years for fuel ethanol production. The ethanol yield and productivity depend on many inhibitory factors during the fermentation process such as temperature, ethanol, compounds released as the result of pretreatment procedures, and osmotic stress. An ideal strain should be able to grow under different stress conditions occurred at different fermentation steps. Development of tolerant yeast strains can be achieved by reprogramming pathways supporting the ethanol metabolism by regulating the energy balance and detoxicification processes. Complex gene interactions should be solved for an in-depth comprehension of the yeast stress tolerance mechanism. Genetic engineering as a powerful biotechnological tool is required to design new strategies for increasing the ethanol fermentation performance. Upregulation of stress tolerance genes by recombinant DNA technology can be a useful approach to overcome inhibitory situations. This review presents the application of several genetic engineering strategies to increase ethanol yield under different stress conditions including inhibitor tolerance, ethanol tolerance, thermotolerance, and osmotolerance.

Role of individual phosphorylation sites for the 14-3-3-protein-dependent activation of yeast neutral trehalase Nth1

Trehalases are important highly conserved enzymes found in a wide variety of organisms and are responsible for the hydrolysis of trehalose that serves as a carbon and energy source as well as a universal stress protectant. Emerging evidence indicates that the enzymatic activity of the neutral trehalase Nth1 in yeast is enhanced by 14-3-3 protein binding in a phosphorylation-dependent manner through an unknown mechanism. In the present study, we investigated in detail the interaction between Saccharomyces cerevisiae Nth1 and 14-3-3 protein isoforms Bmh1 and Bmh2. We determined four residues that are phosphorylated by PKA (protein kinase A) in vitro within the disordered N-terminal segment of Nth1. Sedimentation analysis and enzyme kinetics measurements show that both yeast 14-3-3 isoforms form a stable complex with phosphorylated Nth1 and significantly enhance its enzymatic activity. The 14-3-3-dependent activation of Nth1 is significantly more potent compared with Ca2+-dependent activation. Limited proteolysis confirmed that the 14-3-3 proteins interact with the N-terminal segment of Nth1 where all phosphorylation sites are located. Site-directed mutagenesis in conjunction with the enzyme activity measurements in vitro and the activation studies of mutant forms in vivo suggest that Ser60 and Ser83 are sites primarily responsible for PKA-dependent and 14-3-3-mediated activation of Nth1.

The three trehalases Nth1p, Nth2p and Ath1p participate in the mobilization of intracellular trehalose required for recovery from saline stress in Saccharomyces cerevisiae

Trehalose accumulation is a common response to several stresses in the yeast Saccharomyces cerevisiae. This metabolite protects proteins and membrane lipids from structural damage and helps cells to maintain integrity. Based on genetic studies, degradation of trehalose has been proposed as a required mechanism for growth recovery after stress, and the neutral trehalase Nth1p as the unique degradative activity involved. Here we constructed a collection of mutants for several trehalose metabolism and transport genes and analysed their growth and trehalose mobilization profiles during experiments of saline stress recovery. The behaviour of the triple Deltanth1Deltanth2Deltaath1 and quadruple Deltanth1Deltanth2Deltaath1Deltaagt1 mutant strains in these experiments demonstrates the participation of the three known yeast trehalases Nth1p, Nth2p and Ath1p in the mobilization of intracellular trehalose during growth recovery after saline stress, rules out the participation of the Agt1p H(+)-disaccharide symporter, and allows us to propose the existence of additional new mechanisms for trehalose mobilization after saline stress.

On the biochemical classification of yeast trehalases: Candida albicans contains two enzymes with mixed features of neutral and acid trehalase activities

Two enzymes endowed with trehalase activity are present in Candida albicans. The cytosolic trehalase (Ntc1p), displayed high activity in exponential phase regardless of the carbon source (glucose, trehalose or glycerol). Ntc1p activity was similar in neutral (pH 7.1) or acid (pH 4.5) conditions, strongly inhibited by ATP, weakly stimulated by divalent cations (Ca(2+)or Mn(2+)) and unaffected in the presence of cyclic AMP. The Ntc1p activity decreased in stationary phase, except in glycerol-grown cultures, but the catalytic properties did not change. In turn, the cell wall-linked trehalase (Atc1p) showed elevated activity in resting cells or in cultures growing on trehalose or glycerol. Although Atc1p is subjected to glucose repression, exhaustion of glucose in itself did not increased the activity. Significant Atc1p values could also be measured at neutral or acid pH, but Atc1p was insensitive to ATP, cyclic AMP and divalent cations. These results are in direct contrast with the current classification of yeast trehalases based on their optimum pH. They are also relevant in the light of the proposed use of trehalase inhibitors for the treatment of candidiasis.

Analysis of the vacuolar luminal proteome of Saccharomyces cerevisiae

Despite its large size and the numerous processes in which it is implicated, neither the identity nor the functions of the proteins targeted to the yeast vacuole have been defined comprehensively. In order to establish a methodological platform and protein inventory to address this shortfall, we refined techniques for the purification of 'proteomics-grade' intact vacuoles. As confirmed by retention of the preloaded fluorescent conjugate glutathione-bimane throughout the fractionation procedure, the resistance of soluble proteins that copurify with this fraction to digestion by exogenous extravacuolar proteinase K, and the results of flow cytometric, western and marker enzyme activity analyses, vacuoles prepared in this way retain most of their protein content and are of high purity and integrity. Using this material, 360 polypeptides species associated with the soluble fraction of the vacuolar isolates were resolved reproducibly by 2D gel electrophoresis. Of these, 260 were identified by peptide mass fingerprinting and peptide sequencing by MALDI-MS and liquid chromatography coupled to ion trap or quadrupole TOF tandem MS, respectively. The polypeptides identified in this way, many of which correspond to alternate size and charge states of the same parent translation product, can be assigned to 117 unique ORFs. Most of the proteins identified are canonical vacuolar proteases, glycosidases, phosphohydrolases, lipid-binding proteins or established vacuolar proteins of unknown function, or other proteases, glycosidases, lipid-binding proteins, regulatory proteins or proteins involved in intermediary metabolism, protein synthesis, folding or targeting, or the alleviation of oxidative stress. On the basis of the high purity of the vacuolar preparations, the electrophoretic properties of the proteins identified and the results of quantitative proteinase K protection measurements, many of the noncanonical vacuolar proteins identified are concluded to have entered this compartment for breakdown, processing and/or salvage purposes.

TheArabidopsis thalianatrehalase is a plasma membrane-bound enzyme with extracellular activity

The lack of trehalose accumulation in most plant species has been partly attributed to the presence of an active trehalase. Although trehalose synthesis enzymes are thought to be cytosolic, and previous studies have indicated that trehalase activity is extracellular, the exact location of the enzyme has not yet been established in plant cell. We present evidence that the yet uncharacterised full-length Arabidopsis trehalase is a plasma membrane-bound protein, probably anchored to the membrane through a predicted N-terminal membrane spanning domain. The full-length AtTRE1, when expressed in yeast can functionally substitute for the extracellularly active trehalase Ath1p, by sustaining the growth of an ath1 null mutant strain on trehalose and at pH 4.8. We further demonstrate that AtTRE1 expressed in yeast is plasma membrane-bound as in plant cell. In light of these findings, the regulation of plant cell endogenous trehalose by trehalase is discussed.

The transmembrane domain of acid trehalase mediates ubiquitin-independent multivesicular body pathway sorting

Trehalose serves as a storage source of carbon and plays important roles under various stress conditions. For example, in many organisms trehalose has a critical function in preserving membrane structure and fluidity during dehydration/rehydration. In the yeast Saccharomyces cerevisiae, trehalose accumulates in the cell when the nutrient supply is limited but is rapidly degraded when the supply of nutrients is renewed. Hydrolysis of trehalose in yeast depends on neutral trehalase and acid trehalase (Ath1). Ath1 resides and functions in the vacuole; however, it appears to catalyze the hydrolysis of extracellular trehalose. Little is known about the transport route of Ath1 to the vacuole or how it encounters its substrate. Here, through the use of various trafficking mutants we showed that this hydrolase reaches its final destination through the multivesicular body (MVB) pathway. In contrast to the vast majority of proteins sorted into this pathway, Ath1 does not require ubiquitination for proper localization. Mutagenesis analyses aimed at identifying the unknown targeting signal revealed that the transmembrane domain of Ath1 contains the information sufficient for its selective sequestration into MVB internal vesicles.

Identification of an extracellular acid trehalase and its gene involved in fungal pathogenesis of Metarizium anisopliae

Trehalose is the main sugar in the haemolymph of insects and is a key nutrient source for an insect pathogenic fungus. Secretion of trehalose-hydrolysing enzymes may be a prerequisite for successful exploitation of this resource by the pathogen. An acid trehalase [EC 3.2.1.28] was purified to homogeneity from a culture of a locust-specific pathogen, Metarhizium anisopliae, and its properties were characterized. The gene (ATM1) of this acid trehalase was also isolated. The pure enzyme can efficiently hydrolyze haemolymph trehalose into glucose in vitro. The new acid trehalase appearing in the haemolymph of Locusta migratoria infected with M. anisopliae had the same pI and substrate specificity as the purified fungal acid trehalase, and the concentration of trehalose in the haemolymph decreased sharply after infection. RT-PCR also revealed the ATM1 gene's expression in the haemolymph of the infected insects. Our results indicated that the acid trehalase may serve as an "energy scavenger" and deplete blood trehalose during fungal pathogenesis.

Role of nitrogen and carbon transport, regulation, and metabolism genes for Saccharomyces cerevisiae survival in vivo

Saccharomyces cerevisiae is both an emerging opportunistic pathogen and a close relative of pathogenic Candida species. To better understand the ecology of fungal infection, we investigated the importance of pathways involved in uptake, metabolism, and biosynthesis of nitrogen and carbon compounds for survival of a clinical S. cerevisiae strain in a murine host. Potential nitrogen sources in vivo include ammonium, urea, and amino acids, while potential carbon sources include glucose, lactate, pyruvate, and fatty acids. Using mutants unable to either transport or utilize these compounds, we demonstrated that no individual nitrogen source was essential, while glucose was the most significant primary carbon source for yeast survival in vivo. Hydrolysis of the storage carbohydrate glycogen made a slight contribution for in vivo survival compared with a substantial requirement for trehalose hydrolysis. The ability to sense and respond to low glucose concentrations was also important for survival. In contrast, there was little or no requirement in vivo in this assay for any of the nitrogen-sensing pathways, nitrogen catabolite repression, the ammonium- or amino acid-sensing pathways, or general control. By using auxotrophic mutants, we found that some nitrogenous compounds (polyamines, methionine, and lysine) can be acquired from the host, while others (threonine, aromatic amino acids, isoleucine, and valine) must be synthesized by the pathogen. Our studies provide insights into the yeast-host environment interaction and identify potential antifungal drug targets.

The cellular resistance against oxidative stress (H2O2) is independent of neutral trehalase (Ntc1p) activity in Candida albicans

The protective role of trehalose against oxidative stress caused by hydrogen peroxide in Candida albicans has been investigated in the homozygous mutant ntc1Delta/ntc1Delta, disrupted in the NTC1 gene, which encodes the neutral (cytosolic) trehalase (Ntc1p). After a severe oxidative exposure (50 mM H(2)O(2)), both parental (CAI-4) and ntc1Delta/ntc1Delta exponential-phase cells stored large amounts of intracellular trehalose. In turn, the degree of cell survival was roughly equivalent in both strains, although slightly higher in ntc1Delta/ntc1Delta cultures. The mechanism of 'adaptive tolerance' was functional in the two strains. Thus, a gently oxidative pretreatment (5 mM H(2)O(2)) increased the recovery of cellular viability when it was followed by a severe challenge (50 mM H(2)O(2)); this phenomenon was accompanied by a significant elevation of the endogenous trehalose content. Oxidative stress also induced specific activation of the antioxidant enzymes catalase and glutathione reductase upon gentle oxidative treatment (5 mM H(2)O(2)), whereas superoxide dismutase activity was only activated upon prolonged exposure. Taken together, these results strongly suggest that in C. albicans neutral trehalase activity does not play an essential role in the protective response against oxidative stress. They also suggest that a diminished Ntc1p activity might favour the growth of C. albicans cells subjected to a strong oxidative exposure.

Extracellular trehalose utilization by Saccharomyces cerevisiae

Two haploid strains of Saccharomyces cerevisiae viz. MATalpha and MATa were grown in glucose and trehalose medium and growth patterns were compared. Both strains show similar growth, except for an extended lag phase in trehalose grown cells. In both trehalose grown strains increase in activities of both extracellular trehalase activities and simultaneous decrease in extracellular trehalose level was seen. This coincided with a sharp increase in extracellular glucose level and beginning of log phase of growth. Alcohol production was also observed. Secreted trehalase activity was detected, in addition to periplasmic activity. It appeared that extracellular trehalose was hydrolyzed into glucose by extracellular trehalase activity. This glucose was utilized by the cells for growth. The alcohol formation was due to the fermentation of glucose. Addition of extracellular trehalase caused reduction in the lag phase when grown in trehalose medium, supporting our hypothesis of extracellular utilization of trehalose.

Acid trehalase in yeasts and filamentous fungi: Localization, regulation and physiological function

Yeasts and filamentous fungi are endowed with two different trehalose-hydrolysing activities, termed acid and neutral trehalases according to their optimal pH for enzymatic activity. A wealth of information already exists on fungal neutral trehalases, while data on localization, regulation and function of fungal acid trehalases have remained elusive. The gene encoding the latter enzyme has now been isolated from two yeast species and two filamentous fungi, and sequences encoding putative acid trehalase can be retrieved from available public sequences. Despite weak similarities between amino acids sequences, this type of trehalase potentially harbours either a transmembrane segment or a signal peptide at the N-terminal sequence, as deduced from domain prediction algorithms. This feature, together with the demonstration that acid trehalase from yeasts and filamentous fungi is localized at the cell surface, is consistent with its main role in the utilisation of exogenous trehalose as a carbon source. The growth on this disaccharide is in fact pretty effective in most fungi except in Saccharomyces cerevisiae. This yeast species actually exhibits a "Kluyver effect" on trehalose. Moreover, an oscillatory behaviour reminiscent of what is observed in aerobic glucose-limited continuous cultures at low dilution rate is also observed in batch growth on trehalose. Finally, the S. cerevisiae acid trehalase may also participate in the catabolism of endogenous trehalose by a mechanism that likely requires the export of the disaccharide, its extracellular hydrolysis, and the subsequent uptake of the glucose released. Based on these recent findings, we suggest to rename "acid" and "neutral" trehalases as "extracellular" and "cytosolic" trehalases, which is more adequate to describe their localization and function in the fungal cell.

The ATC1 Gene Encodes a Cell Wall-linked Acid Trehalase Required for Growth on Trehalose in Candida albicans

After screening a Candida albicans genome data base, the product of an open reading frame (IPF 19760/CA2574) with 41% identity to Saccharomyces cerevisiae vacuolar acid trehalase (Ath1p) was identified and named Atc1p. The deduced amino acid sequence shows that Atc1p contains an N-terminal hydrophobic signal peptide and 20 potential sites for N-glycosylation. C. albicans homozygous mutants that lack acid trehalase activity were constructed by gene disruption at the two ATC chromosomal alleles. Analysis of these null mutants shows that Atc1p is localized in the cell wall and is required for growth on trehalose as a carbon source. An Atc1p endowed with acid trehalase activity was obtained by an in vtro transcription-translation coupled system. These results strongly suggest that ATC1 is the structural gene encoding cell wall acid trehalase in C. albicans. Determinations of ATC1 mRNA expression as well as acid trehalase activity in the presence and absence of glucose point out that ATC1 gene is regulated by glucose repression.

Two distinct pathways for trehalose assimilation in the yeast Saccharomyces cerevisiae

The yeast Saccharomyces cerevisiae can synthesize trehalose and also use this disaccharide as a carbon source for growth. However, the molecular mechanism by which extracellular trehalose can be transported to the vacuole and degraded by the acid trehalase Ath1p is not clear. By using an adaptation of the assay of invertase on whole cells with NaF, we showed that more than 90% of the activity of Ath1p is extracellular, splitting of the disaccharide into glucose. We also found that Agt1p-mediated trehalose transport and the hydrolysis of the disaccharide by the cytosolic neutral trehalase Nth1p are coupled and represent a second, independent pathway, although there are several constraints on this alternative route. First, the AGT1/MAL11 gene is controlled by the MAL system, and Agt1p was active in neither non-maltose-fermenting nor maltose-inducible strains. Second, Agt1p rapidly lost activity during growth on trehalose, by a mechanism similar to the sugar-induced inactivation of the maltose permease. Finally, both pathways are highly pH sensitive and effective growth on trehalose occurred only when the medium was buffered at around pH 5.0. The catabolism of trehalose was purely oxidative, and since levels of Ath1p limit the glucose flux in the cells, batch cultures on trehalose may provide a useful alternative to glucose-limited chemostat cultures for investigation of metabolic responses in yeast.

A role for calcium in the regulation of neutral trehalase activity in the fission yeast Schizosaccharomyces pombe

Neutral trehalases mobilize trehalose accumulated by fungal cells as a protective and storage carbohydrate. A structural feature of these enzymes is the presence of an EF-like motif similar to that shown by many Ca2+-binding proteins. In this study we provide direct evidence for physical binding of Ca2+ to neutral trehalase (Ntp1p) of the fission yeast Schizosaccharomyces pombe, and show that aspartic residues at positions 97 and 108 in the conserved putative Ca2+-binding motif of Ntp1p appear to be responsible for this interaction. Mutations in these residues do not interfere with the ability of Ntp1p to associate in vivo with trehalose-6-phosphate synthase, but prevent activation of neutral trehalase triggered by the addition of glucose or by subjecting cells to stressing conditions. Strains expressing Ntp1p variants that are unable to bind Ca2+ partially resemble those devoid of the ntp1+ gene in terms of trehalose hyperaccumulation. Gel filtration of cell extracts from wild-type cells after EDTA treatment or from cells containing Ntp1p with mutations in aspartic acid residues within the Ca2+-binding site revealed that Ntp1p eluted mainly in an inactive conformation instead of the dimeric or trimeric active form of the enzyme. These results suggest that activation of S. pombe Ntp1p under different conditions depends upon Ca2+ binding through the Ca2+-binding motif as a prerequisite for correct enzyme oligomerization to its active form. Given the high degree of conservation of the Ca2+ accommodation site, this might be a general mechanism regulating neutral trehalase activity in other yeasts and filamentous fungi.

Shared control of maltose and trehalose utilization in Candida utilis

Trehalose biosynthesis and its hydrolysis have been extensively studied in yeast, but few reports have addressed the catabolism of exogenously supplied trehalose. Here we report the catabolism of exogenous trehalose by Candida utilis. In contrast to the biphasic growth in glucose, the growth of C. utilis in a mineral medium with trehalose as the sole carbon and energy source is aerobic and exhibits the Kluyver effect. Trehalose is transported into the cell by an inducible trehalose transporter (K M of 8 mM and V MAX of 1.8 mol trehalose min-1 mg cell (dry weight)-1. The activity of the trehalose transporter is high in cells growing in media containing trehalose or maltose and very low or absent during the growth in glucose or glycerol. Similarly, total trehalase activity was increased from about 1.0 mU/mg protein in cells growing in glucose to 39.0 and 56.2 mU/mg protein in cells growing in maltose and trehalose, respectively. Acidic and neutral trehalase activities increased during the growth in trehalose, with neutral trehalase contributing to about 70% of the total activity. In addition to the increased activities of the trehalose transporter and trehalases, growth in trehalose promoted the increase in the activity of alpha-glucosidase and the maltose transporter. These results clearly indicate that maltose and trehalose promote the increase of the enzymatic activities necessary to their catabolism but are also able to stimulate each other's catabolism, as reported to occur in Escherichia coli. We show here for the first time that trehalose induces the catabolism of maltose in yeast.

Osmotic stress signaling and osmoadaptation in yeasts

The ability to adapt to altered availability of free water is a fundamental property of living cells. The principles underlying osmoadaptation are well conserved. The yeast Saccharomyces cerevisiae is an excellent model system with which to study the molecular biology and physiology of osmoadaptation. Upon a shift to high osmolarity, yeast cells rapidly stimulate a mitogen-activated protein (MAP) kinase cascade, the high-osmolarity glycerol (HOG) pathway, which orchestrates part of the transcriptional response. The dynamic operation of the HOG pathway has been well studied, and similar osmosensing pathways exist in other eukaryotes. Protein kinase A, which seems to mediate a response to diverse stress conditions, is also involved in the transcriptional response program. Expression changes after a shift to high osmolarity aim at adjusting metabolism and the production of cellular protectants. Accumulation of the osmolyte glycerol, which is also controlled by altering transmembrane glycerol transport, is of central importance. Upon a shift from high to low osmolarity, yeast cells stimulate a different MAP kinase cascade, the cell integrity pathway. The transcriptional program upon hypo-osmotic shock seems to aim at adjusting cell surface properties. Rapid export of glycerol is an important event in adaptation to low osmolarity. Osmoadaptation, adjustment of cell surface properties, and the control of cell morphogenesis, growth, and proliferation are highly coordinated processes. The Skn7p response regulator may be involved in coordinating these events. An integrated understanding of osmoadaptation requires not only knowledge of the function of many uncharacterized genes but also further insight into the time line of events, their interdependence, their dynamics, and their spatial organization as well as the importance of subtle effects.

The Kluyver effect for trehalose in Saccharomyces cerevisiae

Saccharomyces cerevisiae cells are able to grow using trehalose as a sole source of carbon and energy. However, the biomass yield obtained with trehalose was higher, and the specific growth rate lower, than that obtained with glucose or maltose. The respiratory inhibitor antimycin A prevented cell growth on trehalose, and no ethanol or glycerol was formed during batch growth on this carbon source. Thus, S. cerevisiae exhibits the KLUYVER effect for trehalose: this disaccharide is assimilated and respired, but, in contrast to glucose or maltose, it cannot be fermented. The high-affinity trehalose-H+ symporter encoded by the AGT1 gene is required for growth on trehalose. Analysis of the differences in the metabolism of maltose and trehalose (both disaccharides of glucose transported by active transport systems) indicated that the absence of trehalose fermentation is a consequence of low sugar influx into the cells during growth on this carbon source.

Trehalose and trehalase in Arabidopsis

Trehalase is ubiquitous in higher plants. So far, indications concerning its function are scarce, although it has been implicated in the detoxification of exogenous trehalose. A putative trehalase gene, T19F6.15, has been identified in the genome sequencing effort in Arabidopsis. Here we show that this gene encodes a functional trehalase when its cDNA is expressed in yeast, and that it is expressed in various plant organs. Furthermore, we present results on the distribution and activity of trehalase in Arabidopsis and we describe how inhibition of trehalase by validamycin A affects the plants response to exogenous trehalose (alpha-D-glucopyranosyl-[1, 1]-alpha-D-glucopyranoside). Trehalase activity was highest in floral organs, particularly in the anthers (approximately 700 nkat g(-1) protein) and maturing siliques (approximately 250 nkat g(-1) protein) and much lower in leaves, stems, and roots (less than 50 nkat g(-1) protein). Inhibition of trehalase in vivo by validamycin A led to the accumulation of an endogenous substance that had all the properties of trehalose, and to a strong reduction in sucrose and starch contents in flowers, leaves, and stems. Thus, trehalose appears to be an endogenous substance in Arabidopsis, and trehalose and trehalase may play a role in regulating the carbohydrate allocation in plants.

Reserve carbohydrates metabolism in the yeast Saccharomyces cerevisiae

Glycogen and trehalose are the two glucose stores of yeast cells. The large variations in the cell content of these two compounds in response to different environmental changes indicate that their metabolism is controlled by complex regulatory systems. In this review we present information on the regulation of the activity of the enzymes implicated in the pathways of synthesis and degradation of glycogen and trehalose as well as on the transcriptional control of the genes encoding them. cAMP and the protein kinases Snf1 and Pho85 appear as major actors in this regulation. From a metabolic point of view, glucose-6-phosphate seems the major effector in the net synthesis of glycogen and trehalose. We discuss also the implication of the recently elucidated TOR-dependent nutrient signalling pathway in the control of the yeast glucose stores and its integration in growth and cell division. The unexpected roles of glycogen and trehalose found in the control of glycolytic flux, stress responses and energy stores for the budding process, demonstrate that their presence confers survival and reproductive advantages to the cell. The findings discussed provide for the first time a teleonomic value for the presence of two different glucose stores in the yeast cell.

Role for trehalase during germination of spores in the fission yeast Schizosaccharomyces pombe

Spores from Schizosaccharomyces pombe contain neutral and acid trehalases. When spores from strains disrupted for ntp1(+), which encodes neutral trehalase, were induced to germinate, the onset of the process was markedly delayed as compared to wild-type spores. Further outgrowth was also reduced. Dormant spores lacking neutral trehalase contained twice the amount of trehalose present in wild-type spores and mobilised the intracellular pool of trehalose at a slower rate during germination. Inhibition by phloridzin of the sporulation-specific acid trehalase in ntp1-disrupted spores arrested germination completely while prompting no effect on wild-type spores. These results suggest that the two trehalase enzymes may support the utilisation of trehalose during germination but neutral trehalase is required for a more rapid and efficient process.