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

Evaluating cellular roles and phenotypes associated with trehalose degradation genes in Saccharomyces cerevisiae

In the yeast Saccharomyces cerevisiae, 2 types of trehalase activities have been described. Neutral trehalases (Nth1 and Nth2) are considered to be the main proteins that catalyze intracellular trehalose mobilization. In addition to Nth1 and Nth2, studies have shown that acid trehalase Ath1 is required for extracellular trehalose degradation. Although both neutral and acid-type trehalases have been predominantly investigated in laboratory strains of S. cerevisiae, we sought to examine the phenotypic consequences of disrupting these genes in wild strains. In this study, we constructed mutants of the trehalose degradation pathway (NTH1, NTH2, and ATH1) in 5 diverse S. cerevisiae strains to examine whether published lab strain phenotypes are also exhibited by wild strains. For each mutant, we assessed a number of phenotypes for comparison to trehalose biosynthesis mutants, including trehalose production, glycogen production, cell size, acute thermotolerance, high-temperature growth, sporulation efficiency, and growth on a variety of carbon sources in rich and minimal medium. We found that all trehalase mutants including single deletion nth1Δ, nth2Δ, and ath1Δ, as well as double deletion nth1nth2Δ, accumulated higher intracellular trehalose levels compared to their isogenic wild-type cells. Also, nth1Δ and nth1Δnth2Δ mutants exhibited mild thermal sensitivity, suggesting a potential minor role for trehalose mobilization when cells recover from stress. In addition, we evaluated phenotypes more directly relevant to trehalose degradation, including both extracellular and intracellular trehalose utilization. We discovered that intracellular trehalose hydrolysis is critical for typical spore germination progression, highlighting a role for trehalose in cell cycle regulation, likely as a storage carbohydrate providing glycolytic fuel. Additionally, our work provides further evidence suggesting Ath1 is indispensable for extracellular trehalose utilization as a carbon source, even in the presence of AGT1.

Molecular characterization, carbohydrate metabolism and tolerance to abiotic stress of Eremothecium coryli endophytic isolates from fruits of Momordica indica

Yeasts are unicellular fungi that occur in a wide range of ecological niches, where they perform numerous functions. Furthermore, these microorganisms are used in industrial processes, food production, and bioremediation. Understanding the physiological and adaptive characteristics of yeasts is of great importance from ecological, biotechnological, and industrial perspectives. In this context, we evaluated the abilities to assimilate and ferment different carbon sources, to produce extracellular hydrolytic enzymes, and to tolerate salt stress, heavy metal stress, and UV-C radiation of two isolates of Eremothecium coryli, isolated from Momordica indica fruits. The two isolates were molecularly identified based on sequencing of the 18S-ITS1-5.8S-ITS2 region. Our isolates were able to assimilate nine carbon sources (dextrose, galactose, mannose, cellobiose, lactose, maltose, sucrose, melezitose, and pectin) and ferment three (glucose, maltose, and sucrose). The highest values of cellular dry weight were observed in the sugars maltose, sucrose, and melezitose. We observed the presence of hyphae and pseudohyphae in all assimilated carbon sources. The two isolates were also capable of producing amylase, catalase, pectinase, and proteases, with the highest values of enzymatic activity found in amylase. Furthermore, the two isolates were able to grow in media supplemented with copper, iron, manganese, nickel, and zinc and to tolerate saline stress in media supplemented with 5% NaCl. However, we observed a decrease in CFU at higher concentrations of these metals and NaCl. We also observed morphological changes in the presence of metals, which include changes in cell shape and cellular dimorphisms. The isolates were sensitive to UV-C radiation in the shortest exposure time (1 min). Our findings reinforce the importance of endophytic yeasts for biotechnological and industrial applications and also help to understand how these microorganisms respond to environmental variations caused by human activities.

VdPT1 Encoding a Neutral Trehalase of Verticillium dahliae Is Required for Growth and Virulence of the Pathogen

Verticillum dahliae is a soil-borne phytopathogenic fungus causing destructive Verticillium wilt disease. We previously found a trehalase-encoding gene (VdPT1) in V. dahliae being significantly up-regulated after sensing root exudates from a susceptible cotton variety. In this study, we characterized the function of VdPT1 in the growth and virulence of V. dahliae using its deletion-mutant strains. The VdPT1 deletion mutants (ΔVdPT1) displayed slow colony expansion and mycelial growth, reduced conidial production and germination rate, and decreased mycelial penetration ability and virulence on cotton, but exhibited enhanced stress resistance, suggesting that VdPT1 is involved in the growth, pathogenesis, and stress resistance of V. dahliae. Host-induced silencing of VdPT1 in cotton reduced fungal biomass and enhanced cotton resistance against V. dahliae. Comparative transcriptome analysis between wild-type and mutant identified 1480 up-regulated and 1650 down-regulated genes in the ΔVdPT1 strain. Several down-regulated genes encode plant cell wall-degrading enzymes required for full virulence of V. dahliae to cotton, and down-regulated genes related to carbon metabolism, DNA replication, and amino acid biosynthesis seemed to be responsible for the decreased growth of the ΔVdPT1 strain. In contrast, up-regulation of several genes related to glycerophospholipid metabolism in the ΔVdPT1 strain enhanced the stress resistance of the mutated strain.

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.

Fungal X-Intrinsic Protein Aquaporin from Trichoderma atroviride: Structural and Functional Considerations

The major intrinsic protein (MIP) superfamily is a key part of the fungal transmembrane transport network. It facilitates the transport of water and low molecular weight solutes across biomembranes. The fungal uncharacterized X-Intrinsic Protein (XIP) subfamily includes the full protein diversity of MIP. Their biological functions still remain fully hypothetical. The aim of this study is still to deepen the diversity and the structure of the XIP subfamily in light of the MIP counterparts—the aquaporins (AQPs) and aquaglyceroporins (AQGPs)—and to describe for the first time their function in the development, biomass accumulation, and mycoparasitic aptitudes of the fungal bioagent Trichoderma atroviride. The fungus-XIP clade, with one member (TriatXIP), is one of the three clades of MIPs that make up the diversity of T. atroviride MIPs, along with the AQPs (three members) and the AQGPs (three members). TriatXIP resembles those of strict aquaporins, predicting water diffusion and possibly other small polar solutes due to particularly wider ar/R constriction with a Lysine substitution at the LE2 position. The XIP loss of function in ∆TriatXIP mutants slightly delays biomass accumulation but does not impact mycoparasitic activities. ∆TriatMIP forms colonies similar to wild type; however, the hyphae are slightly thinner and colonies produce rare chlamydospores in PDA and specific media, most of which are relatively small and exhibit abnormal morphologies. To better understand the molecular causes of these deviant phenotypes, a wide-metabolic survey of the ∆TriatXIPs demonstrates that the delayed growth kinetic, correlated to a decrease in respiration rate, is caused by perturbations in the pentose phosphate pathway. Furthermore, the null expression of the XIP gene strongly impacts the expression of four expressed MIP-encoding genes of T. atroviride, a plausible compensating effect which safeguards the physiological integrity and life cycle of the fungus. This paper offers an overview of the fungal XIP family in the biocontrol agent T. atroviride which will be useful for further functional analysis of this particular MIP subfamily in vegetative growth and the environmental stress response in fungi. Ultimately, these findings have implications for the ecophysiology of Trichoderma spp. in natural, agronomic, and industrial systems.

The secreted acid trehalase encoded by the CgATH1 gene is involved in Candida glabrata virulence

BACKGROUND

Candida glabrata yeast is the second cause of candidiasis worldwide. Differs from other yeasts since assimilates only glucose and trehalose (a characteristic used in rapid identification tests for this pathogen) by secreting into the medium a highly active acid trehalase encoded by the CgATH1 gene.

OBJECTIVE

This study aimed to characterise the function of the acid trehalase in the physiopathology of C. glabrata.

METHODS

Gene deletion was performed to obtain a mutant ath1Δ strain, and the ability of the ath1Δ strain to grow in trehalase, or the presence of trehalase activity in the ath1Δ yeast cells, was verified. We also tested the virulence of the ath1Δ strain in a murine model of infection.

FINDINGS

The ath1Δ mutant strain grows normally in the presence of glucose, but loses its ability to grow in trehalose. Due to the high acid trehalase activity present in wild-type cells, the cytoplasmic neutral trehalase activity is only detected in the ath1Δ strain. We also observed a significantly lower virulence of the ath1Δ strain in a murine model of infection with either normal or immunocompromised mice.

MAIN CONCLUSIONS

The acid trehalase is involved in the hydrolysis of external trehalose by C. glabrata, and the enzyme also plays a major virulence role during infectivity.

The link between yeast cell wall porosity and plasma membrane permeability after PEF treatment

An investigation of the yeast cell resealing process was performed by studying the absorption of the tetraphenylphosphonium (TPP⁺) ion by the yeast Saccharomyces cerevisiae. It was shown that the main barrier for the uptake of such TPP⁺ ions is the cell wall. An increased rate of TPP⁺ absorption after treatment of such cells with a pulsed electric field (PEF) was observed only in intact cells, but not in spheroplasts. The investigation of the uptake of TPP⁺ in PEF treated cells exposed to TPP⁺ for different time intervals also showed the dependence of the absorption rate on the PEF strength. The modelling of the TPP⁺ uptake recovery has also shown that the characteristic decay time of the non-equilibrium (PEF induced) pores was approximately a few tens of seconds and this did not depend on the PEF strength. A further investigation of such cell membrane recovery process using a florescent SYTOX Green nucleic acid stain dye also showed that such membrane resealing takes place over a time that is like that occurring in the cell wall. It was thus concluded that the similar characteristic lifetimes of the non-equilibrium pores in the cell wall and membrane after exposure  to  PEF indicate a strong coupling between these parts of the cell.

Metabolic constraints drive self-organization of specialized cell groups

How phenotypically distinct states in isogenic cell populations appear and stably co-exist remains unresolved. We find that within a mature, clonal yeast colony developing in low glucose, cells arrange into metabolically disparate cell groups. Using this system, we model and experimentally identify metabolic constraints sufficient to drive such self-assembly. Beginning in a uniformly gluconeogenic state, cells exhibiting a contrary, high pentose phosphate pathway activity state, spontaneously appear and proliferate, in a spatially constrained manner. Gluconeogenic cells in the colony produce and provide a resource, which we identify as trehalose. Above threshold concentrations of external trehalose, cells switch to the new metabolic state and proliferate. A self-organized system establishes, where cells in this new state are sustained by trehalose consumption, which thereby restrains other cells in the trehalose producing, gluconeogenic state. Our work suggests simple physico-chemical principles that determine how isogenic cells spontaneously self-organize into structured assemblies in complimentary, specialized states.

The trehalose protective mechanism during thermal stress in Saccharomyces cerevisiae: the roles of Ath1 and Agt1

Trehalose on both sides of the bilayer is a requirement for full protection of membranes against stress. It was not known yet how trehalose, synthesized in the cytosol when dividing Saccharomyces cerevisiae cells are shifted from 28°C to 40°C, is transported to the outside and degraded when cells return to 28°C. According to our results, the lack of Agt1, a trehalose transporter, although had not affected trehalose synthesis, reduced cell tolerance to 51°C and increased lipid peroxidation. The damage was reversed when external trehalose was added during 40°C adaptation, confirming that the reason for the agt1Δ sensitivity is the absence of trehalose at the outside of the lipid bilayer. The 40-28°C condition caused cytosolic trehalase (Nth1) activation, reducing intracellular trehalose and, consequently, the survival rates after 51°C. Although lower than nth1Δ strain, cells deficient in acid trehalase (ath1Δ)  maintained increased trehalose levels after 40°C-28°C shift, which conferred protection against 51°C. Both Ath1 and Agt1 were found into vesicles near to plasma membrane in response to stress. This suggests that Agt1 containing vesicles would fuse with the membrane under 40°C to transport part of the cytosolic trehalose to the outside. By a similar mechanism, Ath1 would reach the cell surface to hydrolyze the external trehalose but only when the stress would be over. Corroborating this conclusion, Ath1 activity in soluble cell-free extracts increased after 40°C adaptation but decreased when cells returned to 28°C. During 40°C, Ath1 is confined into vesicles, avoiding the cleavage of the outside trehalose.

Comparative transcriptome analysis reveals regulatory networks and key genes of microsclerotia formation in the cotton vascular wilt pathogen

Verticillium dahliae is a soil-borne, hemibiotrophic phytopathogenic fungus that causes Verticillium wilt in a broad range of economic crops. The microsclerotia (MS), which act as the main host inoculum, can survive long-term in soil resulting in uncontrollable disease. In order to clarify the mechanism of MS formation, we sequenced the whole genome-wide expression profile of V. dahliae strain V991. Compared with M1 (no MS formation), during the process of MS formation and maturation, 1354, 1571, and 1521 unique tags were significantly regulated in M2, M3, and M4 library, respectively. During MS formation, melanin synthesis-related genes were preferentially upregulated. The process is more likely to regulated by transcription factors (TFs) including C₂H₂, Zn₂Cys₆, bZIP, and fungal-specific TF domain-containing proteins; additionally, G-protein coupled receptors, Ca²⁺, small GTPases, and cAMP were involved in signalling transduction. Protein kinase-encoding (VDAG_06474) and synthase-encoding (VDAG_05314) genes were demonstrated to negatively and positively influence MS production, respectively. The gene expression dynamics revealed during MS formation provide comprehensive theoretical knowledge to further understanding of the metabolism and regulation of MS development in V. dahliae, potentially providing targets to control Verticillium wilt through interfering MS formation.

Experimental evolution: its principles and applications in developing stress-tolerant yeasts

Stress tolerance and resistance in industrial yeast strains are important attributes for cost-effective bioprocessing. The source of stress-tolerant yeasts ranges from extremophilic environments to laboratory engineered strains. However, industrial stress-tolerant yeasts are very rare in nature as the natural environment forces them to evolve traits that optimize survival and reproduction and not the ability to withstand harsh habitat-irrelevant industrial conditions. Experimental evolution is a frequent method used to uncover the mechanisms of evolution and microbial adaption towards environmental stresses. It optimizes biological systems by means of adaptation to environmental stresses and thus has immense power of development of robust stress-tolerant yeasts. This mini-review briefly outlines the basics and implications of evolution experiments and their applications to industrial biotechnology. This work is meant to serve as an introduction to those new to the field of experimental evolution, and as a guide to biologists working in the field of yeast stress response. Future perspectives of experimental evolution for potential biotechnological applications have also been elucidated.

Extracellular maltotriose hydrolysis by Saccharomyces cerevisiae cells lacking the AGT1 permease

In brewing, maltotriose is the least preferred sugar for uptake by Saccharomyces cerevisiae cells. Although the AGT1 permease is required for efficient maltotriose fermentation, we have described a new phenotype in some agt1Δ strains of which the cells do not grow on maltotriose during the first 3-4 days of incubation, but after that, they start to grow on the sugar aerobically. Aiming to characterize this new phenotype, we performed microarray gene expression analysis which indicated upregulation of high-affinity glucose transporters (HXT4, HXT6 and HXT7) and α-glucosidases (MAL12 and IMA5) during this delayed cellular growth. Since these results suggested that this phenotype might be due to extracellular hydrolysis of maltotriose, we attempted to detect glucose in the media during growth. When an hxt-null agt1Δ strain was grown on maltotriose, it also showed the delayed growth on this carbon source, and glucose accumulated in the medium during maltotriose consumption. Considering that the poorly characterized α-glucosidase encoded by IMA5 was among the overexpressed genes, we deleted this gene from an agt1Δ strain that showed delayed growth on maltotriose. The ima5Δ agt1Δ strain showed no maltotriose utilization even after 200 h of incubation, suggesting that IMA5 is likely responsible for the extracellular maltotriose hydrolysis.

SIGNIFICANCE AND IMPACT OF THE STUDY

Maltotriose is the second most abundant sugar present in brewing. However, many yeast strains have difficulties to consume maltotriose, mainly because of its low uptake rate by the yeast cells when compared to glucose and maltose uptake. The AGT1 permease is required for efficient maltotriose fermentation, but some strains deleted in this gene are still able to grow on maltotriose after an extensive lag phase. This manuscript shows that such delayed growth on maltotriose is a consequence of extracellular hydrolysis of the sugar. Our results also indicate that the IMA5-encoded α-glucosidase is likely the enzyme responsible for this phenotype.

Evolutionary and structure-function analysis elucidates diversification of prokaryotic and eukaryotic trehalases

Trehalase catalyses the breakdown of trehalose into two glucose moieties and is ubiquitous in all organisms. Here, we provide insights into the enigmatic origin and evolution of trehalase in major species. Study of taxonomic distribution, orthology, phylogeny and functional domains indicated that trehalase possibly originates from bacteria and was transmitted to other taxa through horizontal gene transfer. Domain analysis showed that glycosyl hydrolase family 37 is present in most of the sequences and represents dominant activity during evolution, and also, illustrating that cytosolic trehalase is primitive than its transmembrane form. Furthermore, it was observed that trehalase went through domain rearrangement to facilitate its activity in adverse environmental conditions like acidic pH. Gene context analysis depicts that trehalase neighbourhood consists of sugar transport and lipid metabolism genes. This highlights their relatedness in metabolic activity and similarity in gene regulation, respectively. Evolutionary and selection pressure analysis demonstrated that trehalase genes were duplicated and evolved under purifying selection, following horizontal gene transfer. Moreover, site-specific rate of evolution emphasized conservation of functionally important residues. In comparison with acid trehalase, neutral trehalase has an extra N-terminal extension. This study serves as an instigation to understand evolution and functionality of trehalase across diverse species. Communicated by Ramaswamy H. Sarma.

Interaction of storage carbohydrates and other cyclic fluxes with central metabolism: A quantitative approach by non-stationary 13C metabolic flux analysis

13C labeling experiments in aerobic glucose limited cultures of Saccharomyces cerevisiae at four different growth rates (0.054; 0.101, 0.207, 0.307 h-1) are used for calculating fluxes that include intracellular cycles (e.g., storage carbohydrate cycles, exchange fluxes with amino acids), which are rearranged depending on the growth rate. At low growth rates the impact of the storage carbohydrate recycle is relatively more significant than at high growth rates due to a higher concentration of these materials in the cell (up to 560-fold) and higher fluxes relative to the glucose uptake rate (up to 16%). Experimental observations suggest that glucose can be exported to the extracellular space, and that its source is related to storage carbohydrates, most likely via the export and subsequent extracellular breakdown of trehalose. This hypothesis is strongly supported by 13C-labeling experimental data, measured extracellular trehalose, and the corresponding flux estimations.

Effect of acid trehalase (ATH) on impaired yeast vacuolar activity

In this study, this protein was overexpressed in yeast cells grown on trehalose-containing medium to assess its impact on yeast vacuolar activity. ATH was confirmed to be located in both cell surface and vacuoles and the overexpression of ATH was observed to decrease vacuolar activity. Therefore, an assumption was suggested to explain this phenomenon as follows: when grown on containing trehalose medium, the ATH localization at cellular periplasm, but not the vacuole, is prioritized to utilize the extracellular trehalose for cell growth. The multivesicular body pathway (MVB pathway) via which ATH is transported into vacuoles is believed to be down-regulated to favor the accumulation of ATH at cell surface area. By extension, other vacuolar proteins travelling through MVB pathway to reach yeast vacuoles likely also suffer the down regulation. It can be concluded that acid trehalase may contribute down regulation of other vacuolar proteins through MVB pathway. This study suggests that it is a potential of acid trehalase (ATH) on impaired activity of yeast vacuolar.

Cell Surface Interference with Plasma Membrane and Transport Processes in Yeasts

The wall of the yeast Saccharomyces cerevisiae is a shell of about 120 nm thick, made of two distinct layers, which surrounds the cell. The outer layer is constituted of highly glycosylated proteins and the inner layer is composed of β-glucan and chitin. These two layers are interconnected through covalent linkages leading to a supramolecular architecture that is characterized by physical and chemical properties including rigidity, porosity and biosorption. The later property results from the presence of highly negative charged phosphate and carboxylic groups of the cell wall proteins, allowing the cell wall to act as an efficient barrier to metals ions, toxins and organic compounds. An intimate connection between cell wall and plasma membrane is indicated by the fact that changes in membrane fluidity results in change in cell wall nanomechanical properties. Finally, cell wall contributes to transport processes through the use of dedicated cell wall mannoproteins, as it is the case for Fit proteins implicated in the siderophore-iron bound transport and the Tir/Dan proteins family in the uptake of sterols.

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.

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.

Developmental cell fate and virulence are linked to trehalose homeostasis in Cryptococcus neoformans

Among pathogenic environmental fungi, spores are thought to be infectious particles that germinate in the host to cause disease. The meningoencephalitis-causing yeast Cryptococcus neoformans is found ubiquitously in the environment and sporulates in response to nutrient limitation. While the yeast form has been studied extensively, relatively little is known about spore biogenesis, and spore germination has never been evaluated at the molecular level. Using genome transcript analysis of spores and molecular genetic approaches, we discovered that trehalose homeostasis plays a key role in regulating sporulation of C. neoformans, is required for full spore viability, and influences virulence. Specifically, we found that genes involved in trehalose metabolism, including a previously uncharacterized secreted trehalase (NTH2), are highly overrepresented in dormant spores. Deletion of the two predicted trehalases in the C. neoformans genome, NTH1 and NTH2, resulted in severe defects in spore production, a decrease in spore germination, and an increase in the production of alternative developmental structures. This shift in cell types suggests that trehalose levels modulate cell fate decisions during sexual development. We also discovered that deletion of the NTH2 trehalase results in hypervirulence in a murine model of infection. Taken together, these data show that the metabolic adaptations that allow this fungus to proliferate ubiquitously in the environment play unexpected roles in virulence in the mammalian host and highlight the complex interplay among the processes of metabolism, development, and pathogenesis.

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.

Regulation of trehalase expression inhibits apoptosis in diapause cysts of Artemia

Trehalase, which specifically hydrolyses trehalose into glucose, plays an important role in the metabolism of trehalose. Large amounts of trehalose are stored in the diapause encysted embryos (cysts) of Artemia, which are not only vital to their extraordinary stress resistance, but also provide a source of energy for development after diapause is terminated. In the present study, a mechanism for the transcriptional regulation of trehalase was described in Artemia parthenogenetica. A trehalase-associated protein (ArTAP) was identified in Artemia-producing diapause cysts. ArTAP was found to be expressed only in diapause-destined embryos. Further analyses revealed that ArTAP can bind to a specific intronic segment of a trehalase gene. Knockdown of ArTAP by RNAi resulted in the release of cysts with coarse shells in which two chitin-binding proteins were missing. Western blotting showed that the level of trehalase was increased and apoptosis was induced in these ArTAP-knockdown cysts compared with controls. Taken together, these results show that ArTAP is a key regulator of trehalase expression which, in turn, plays an important role in trehalose metabolism during the formation of diapause cysts.

RNA-seq analyses of gene expression in the microsclerotia of Verticillium dahliae

Background

The soilborne fungus, Verticillium dahliae, causes Verticillium wilt disease in plants. Verticillium wilt is difficult to control since V. dahliae is capable of persisting in the soil for 10 to 15 years as melanized microsclerotia, rendering crop rotation strategies for disease control ineffective. Microsclerotia of V. dahliae overwinter and germinate to produce infectious hyphae that give rise to primary infections. Consequently, microsclerotia formation, maintenance, and germination are critically important processes in the disease cycle of V. dahliae.

Results

To shed additional light on the molecular processes that contribute to microsclerotia biogenesis and melanin synthesis in V. dahliae, three replicate RNA-seq libraries were prepared from 10 day-old microsclerotia (MS)-producing cultures of V. dahliae, strain VdLs.17 (average = 52.23 million reads), and those not producing microsclerotia (NoMS, average = 50.58 million reads). Analyses of these libraries for differential gene expression revealed over 200 differentially expressed genes, including up-regulation of melanogenesis-associated genes tetrahydroxynaphthalene reductase (344-fold increase) and scytalone dehydratase (231-fold increase), and additional genes located in a 48.8 kilobase melanin biosynthetic gene cluster of strain VdLs.17. Nearly 50% of the genes identified as differentially expressed in the MS library encode hypothetical proteins. Additional comparative analyses of gene expression in V. dahliae, under growth conditions that promote or preclude microsclerotial development, were conducted using a microarray approach with RNA derived from V. dahliae strain Dvd-T5, and from the amicrosclerotial vdh1 strain. Differential expression of selected genes observed by RNA-seq or microarray analysis was confirmed using RT-qPCR or Northern hybridizations.

Conclusion

Collectively, the data acquired from these investigations provide additional insight into gene expression and molecular processes that occur during MS biogenesis and maturation in V. dahliae. The identified gene products could therefore potentially represent new targets for disease control through prevention of survival structure development.

Impact of temperature stress and validamycin A on compatible solutes and fumonisin production in F. verticillioides: role of trehalose-6-phosphate synthase

Fusarium verticillioides is a pathogen of maize that causes root, stalk and ear rot and produces fumonisins, toxic secondary metabolites associated with disease in livestock and humans. Environmental stresses such as heat and drought influence disease severity and toxin production, but the effects of abiotic stress on compatible solute production by F. verticillioides have not been fully characterized. We found that decreasing the growth temperature leads to a long-term reduction in polyol levels, whereas increasing the temperature leads to a transient increase in polyols. The effects of temperature shifts on trehalose levels are opposite the effects on polyols and more dramatic. Treatment with validamycin A, a trehalose analog with antifungal activity, leads to a rapid reduction in trehalose levels, despite its known role as a trehalase inhibitor. Mutant strains lacking TPS1, which encodes a putative trehalose-6-phosphate synthase, have altered growth characteristics, do not produce detectable amounts of trehalose under any condition tested, and accumulate glycogen at levels significantly higher than wild-type F. verticillioides. TPS1 mutants also produce significantly less fumonisin than wild type and are also less pathogenic than wild type on maize. These data link trehalose biosynthesis, secondary metabolism, and disease, and suggest that trehalose metabolic pathways may be a viable target for the control of Fusarium diseases and fumonisin contamination of maize.

Substrate cycles in Penicillium chrysogenum quantified by isotopic non-stationary flux analysis

Background

Penicillium chrysogenum, the main production strain for penicillin-G, has a high content of intracellular carbohydrates, especially reduced sugars such as mannitol, arabitol, erythritol, as well as trehalose and glycogen. In previous steady state ¹³C wash-in experiments a delay of labeling enrichments in glycolytic intermediates was observed, which suggests turnover of storage carbohydrates. The turnover of storage pools consumes ATP which is expected to reduce the product yield for energy demanding production pathways like penicillin-G.

Results

In this study, a ¹³C labeling wash-in experiment of 1 hour was performed to systematically quantify the intracellular flux distribution including eight substrate cycles. The experiments were performed using a mixed carbon source of 85% Cmol_Glc/Cmol_Glc+EtOH labeled glucose (mixture of 90% [1-¹³C₁] and 10% [U-¹³C₆]) and 15% ethanol [U-¹³C₂]. It was found, that (1) also several extracellular pools are enriched with ¹³C labeling rapidly (trehalose, mannitol, and others), (2) the intra- to extracellular metabolite concentration ratios were comparable for a large set of metabolites while for some carbohydrates (mannitol, trehalose, and glucose) the measured ratios were much higher.

Conclusions

The fast enrichment of several extracellular carbohydrates and a concentration ratio higher than the ratio expected from cell lysis (2%) indicate active (e.g. ATP consuming) transport cycles over the cellular membrane. The flux estimation indicates, that substrate cycles account for about 52% of the gap in the ATP balance based on metabolic flux analysis.

Biochemical properties of an extracellular trehalase from Malbranchea pulchella var. Sulfurea

The thermophilic fungus Malbranchea pulchella var. sulfurea produced good amounts of extracellular trehalase activity when grown for long periods on starch, maltose or glucose as the main carbon source. Studies with young cultures suggested that the main role of the extracellular acid trehalase is utilizing trehalose as a carbon source. The specific activity of the purified enzyme in the presence of manganese (680 U/mg protein) was comparable to that of other thermophilic fungi enzymes, but many times higher than the values reported for trehalases from other microbial sources. The apparent molecular mass of the native enzyme was estimated to be 104 kDa by gel filtration and 52 kDa by SDS-PAGE, suggesting that the enzyme was composed by two subunits. The carbohydrate content of the purified enzyme was estimated to be 19 % and the pi was 3.5. The optimum pH and temperature were 5.0-5.5 and 55° C, respectively. The purified enzyme was stimulated by manganese and inhibited by calcium ions, and insensitive to ATP and ADP, and 1 mM silver ions. The apparent K(M) values for trehalose hydrolysis by the purified enzyme in the absence and presence of manganese chloride were 2.70 ± 0.29 and 2.58 ± 0.13 mM, respectively. Manganese ions affected only the apparent V(max), increasing the catalytic efficiency value by 9.2-fold. The results reported herein indicate that Malbranchea pulchella produces a trehalase with mixed biochemical properties, different from the conventional acid and neutral enzymes and also from trehalases from other thermophilic fungi.

Plant-type trehalose synthetic pathway in cryptosporidium and some other apicomplexans

BACKGROUND

The trehalose synthetic pathway is present in bacteria, fungi, plants and invertebrate animals, but is absent in vertebrates. This disaccharide mainly functions as a stress protectant against desiccation, heat, cold and oxidation. Genes involved in trehalose synthesis have been observed in apicomplexan parasites, but little was known about these enzymes. Study on trehalose synthesis in apicomplexans would not only shed new light into the evolution of this pathway, but also provide data for exploring this pathway as novel drug target.

METHODOLOGY/PRINCIPAL FINDINGS

We have observed the presence of the trehalose synthetic pathway in Cryptosporidium and other apicomplexans and alveolates. Two key enzymes (trehalose 6-phosphate synthase [T6PS; EC 2.4.1.15] and trehalose phosphatase [TPase; EC 3.1.3.12] are present as Class II bifunctional proteins (T6PS-TPase) in the majority of apicomplexans with the exception of Plasmodium species. The enzyme for synthesizing the precursor (UDP-glucose) is homologous to dual-substrate UDP-galactose/glucose pyrophosphorylases (UGGPases), rather than the "classic" UDP-glucose pyrophosphorylase (UGPase). Phylogenetic recontructions indicate that both T6PS-TPases and UGGPases in apicomplexans and other alveolates are evolutionarily affiliated with stramenopiles and plants. The expression level of T6PS-TPase in C. parvum is highly elevated in the late intracellular developmental stage prior to or during the production of oocysts, implying that trehalose may be important in oocysts as a protectant against environmental stresses. Finally, trehalose has been detected in C. parvum oocysts, thus confirming the trehalose synthetic activity in this parasite.

CONCLUSIONS/SIGNIFICANCE

A trehalose synthetic pathway is described in the majority of apicomplexan parasites including Cryptosporidium and the presence of trehalose was confirmed in the C. parvum oocyst. Key enzymes in the pathway (i.e., T6PS-TPase and UGGPase) are plant-type and absent in humans and animals, and may potentially serve as novel drug targets in the apicomplexans.

The Saccharomyces cerevisiae vacuolar acid trehalase is targeted at the cell surface for its physiological function

Previous studies in the yeast Saccharomyces cerevisiae have proposed a vacuolar localization for Ath1, which is difficult to reconcile with its ability to hydrolyze exogenous trehalose. We used fluorescent microscopy to show that the red fluorescent protein mCherry fused to the C-terminus of Ath1, although mostly localized in the vacuole, was also targeted to the cell surface. Also, hybrid Ath1 truncates fused at their C-terminus with the yeast internal invertase revealed that a 131 amino acid N-terminal fragment of Ath1was sufficient to target the fusion protein to the cell surface, enabling growth of the suc2Delta mutant on sucrose. The unique transmembrane domain appeared to be indispensable for the production of a functional Ath1, and its removal abrogated invertase secretion and growth on sucrose. Finally, the physiological significance of the cell-surface localization of Ath1 was established by showing that fusion of the signal peptide of invertase to N-terminal truncated Ath1 allowed the ath1Delta mutant to grow on trehalose, whereas the signal sequence of the vacuolar-targeted Pep4 constrained Ath1 in the vacuole and prevented growth of this mutant on trehalose. Use of trafficking mutants that impaired Ath1 delivery to the vacuole abrogated neither its activity nor its growth on exogenous trehalose.

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.

Physiological implication of intracellular trehalose and mannitol changes in response of entomopathogenic fungus Beauveria bassiana to thermal stress

To explore possible role of intracellular trehalose accumulation in fungal tolerance to summer-like thermal stress, 3-day colonies of Beauveria bassiana grown on a glucose-free medium at 25 degrees C were separately exposed to 35, 37.5 and 40 degrees C for 1-18 h, respectively. Trehalose accumulation in stressed mycelia increased from initial 4.2 to 88.3, 74.7 and 65.5 mg g(-1) biomass after 6-h stress at 35, 37.5 and 40 degrees C, respectively, while intracellular mannitol level generally declined with higher temperatures and longer stress time. The stress-enhanced trehalose level was significantly correlated to decreased trehalase activity (r(2) = 0.73) and mannitol content (r(2) = 0.38), which was inversely correlated to the activity of mannitol dehydrogenase (r(2) = 0.41) or mannitol 1-phosphate dehydrogenase (r(2) = 0.30) under the stresses. All stressed cultures were successfully recovered at 25 degrees C but their vigor depended on stressful temperature, time length and the interaction of both (r (2) = 0.98). The highest level of 6-h trehalose accumulation at 35 degrees C was found enhancing the tolerance of the stressed cultures to the greater stress of 48 degrees C. The results suggest that the trehalose accumulation result partially from metabolized mannitol and contribute to the fungal thermotolerance. Trehalase also contributed to the thermotolerance by hydrolyzing accumulated trehalose under the conditions of thermal stress and recovery.

Relatedness of medically important strains of Saccharomyces cerevisiae as revealed by phylogenetics and metabolomics

Ten medically important Saccharomyces strains, comprising six clinical isolates of Saccharomyces cerevisiae and four probiotic strains of Saccharomyces boulardii, were characterized at the genetic and metabolic level and compared with non-medical, commercial yeast strains used in baking and wine-making. Strains were compared by genetic fingerprinting using amplified fragment length polymorphism (AFLP) analysis, by ribosomal DNA ITS1 sequencing and by metabolic footprinting using both direct injection mass spectrometry (DIMS) and gas chromatography-time of flight-mass spectrometry (GC-ToF-MS). Overall, the clinical isolates fell into different groupings when compared with the non-medical strains, with good but not perfect correlation amongst strains at both the genetic and metabolic levels. Probiotic strains of S. boulardii that are used therapeutically to treat human gastro-intestinal tract disorders showed tight clustering both genetically and metabolically. Metabolomics was found to be of value both as a taxonomic tool and as a means to investigate anomalous links between genotype and phenotype. Key discriminatory metabolites were identified when comparing the three main groups of clinical, probiotic and non-medical strains and included molecules such as trehalose, myo-inositol, lactic acid, fumaric acid and glycerol 3-phosphate. This study confirmed the link between a subset of clinical isolates and baking or probiotic strains but also highlighted that in general the clinical strains were more diverse at both the genomic and metabolic levels.

The major pathways of carbohydrate metabolism in the ectomycorrhizal basidiomycete Laccaria bicolor S238N

The primary carbohydrate metabolism of an ectomycorrhizal fungus and its transcriptional regulation has never been characterized at the genome scale although it plays a fundamental role in the functioning of the symbiosis. In this study, the genome sequence of the ectomycorrhizal basidiomycete Laccaria bicolor S238N-H82 was explored to construct a comprehensive genome-wide inventory of pathways involved in primary carbohydrate metabolism. Several genes and gene families were annotated, including those of the glycolysis, pentose phosphate pathway, tricarboxylic acid cycle, and trehalose and mannitol metabolism. The transcriptional regulation of these pathways was studied using whole-genome expression oligoarrays and quantitative polymerase chain reaction in free-living mycelium, ectomycorrhizas and fruiting bodies. Pathways of carbohydrate biosynthesis and catabolism are identical in L. bicolor compared with other sequenced saprotrophic basidiomycetes. Ectomycorrhiza and fruiting body development induced the regulation of a restricted set of transcripts of the glycolytic, mannitol and trehalose metabolisms.

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.

Revised procedures for yeast metabolites extraction: application to a glucose pulse to carbon-limited yeast cultures, which reveals a transient activation of the purine salvage pathway

In this study we have revised our original procedure of yeast metabolites extraction. We showed that: (a) less than 5% of intracellular metabolites leaks out during the step of rapid arrest of cellular metabolism by quenching yeast cells into a 60% methanol solution kept at -40 degrees C; and (b) with a few exception, the stability of metabolites were not altered during the 3 min boiling procedure in a buffered ethanol solution. However, there was a loss of external added metabolites of 5-30%, depending on the type of metabolites. This was mainly attributable to their retention on cellular debris after ethanol treatment, which prevented centrifugation of the cellular extracts before evaporation of ethanol. We further simplified our previous high-performance ionic chromatography (HPIC) techniques for easier, more reliable and robust quantitative measurements of organic acids, sugar phosphates and sugar nucleotides, and extended these techniques to purine and pyrimidine bases, using a variable wavelength detector set at 220 and 260 nm in tandem with a pulsed electrochemical or suppressed conductivity detector. These protocols were successfully applied to a glucose pulse to carbon-limited yeast cultures on purines metabolism. This study showed that glucose induced a fast activation of the purine salvage pathway, as indicated by a transient drop of ATP and ADP with a concomitant rise of IMP and inosine. This metabolic perturbation was accompanied by a rapid increase in the activity of the ISN1-encoded specific IMP-5'-nucleotidase. The mechanism of this activation remains to be determined.

Solubilization and characterization of a cell wall-bound trehalase from ascospores of the fission yeast Schizosaccharomyces pombe

The genome of the fission yeast Schizosaccharomyces pombe lacks sequence homologs to ath1 genes coding for acid trehalases in other yeasts or filamentous fungi. However, acid trehalase activity is present at the spore stage in the life cycle of the fission yeast. The enzyme responsible for this activity behaves as a surface enzyme covalently linked to the spore cell walls in both wild-type and ntp1 mutant strains devoid of neutral trehalase. Lytic treatment of particulated cell wall fractions allowed the solubilization of the enzyme into an active form. We have characterized this soluble enzyme and found that its kinetic parameters, optimum pH and temperature, thermal denaturation and salt responses are closely similar to other conventional acid trehalases. Hence, this rather unusual enzyme can be recognized as acid trehalase by its biochemical properties although it does not share genetic homology with other known acid trehalases. The potential role of such acid trehalase in the mobilization of trehalose is discussed.

Isoforms of trehalase and invertase of Fusarium oxysporum

Enzymatic assays and native PAGE were used to study trehalase and invertase activities, depending on culture age and different sugar conditions, in cell-free extracts, culture filtrates and ribosomal wash of Fusarium oxysporum. The activity of invertase preceded that of trehalase; in the exponential phase of growth, mainly invertase activity was produced, whereas trehalase activity was high in the stationary phase. In this last phase of growth, the activity of intracellular trehalase was repressed by monosaccharides, whereas disaccharides, especially lactose and starch, enhanced the activity of intracellular and extracellular trehalase. However, invertase activity was not repressed under these conditions and had the maximal activity in the presence of saccharose. Intracellular trehalase appeared in a single, high-molecular weight (120 kDa) form, whereas the extracellular enzyme appeared in a single, low-molecular weight (60 kDa) form. The activity pattern of invertase isoforms indicated the occurrence of three forms of intracellular enzyme with the main activity band at 120 kDa and two isoforms of extracellular enzyme. In the ribosomal wash, high-molecular weight isoforms of both trehalase and invertase were identified. A possible role of trehalase and invertase in carbohydrate metabolism of fungal pathogens is also discussed.

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.

A highly thermostable trehalase from the thermophilic bacterium Rhodothermus marinus

Trehalases play a central role in the metabolism of trehalose and can be found in a wide variety of organisms. A periplasmic trehalase (alpha,alpha-trehalose glucohydrolase, EC 3.2.1.28) from the thermophilic bacterium Rhodothermus marinus was purified and the respective encoding gene was identified, cloned and overexpressed in Escherichia coli. The recombinant trehalase is a monomeric protein with a molecular mass of 59 kDa. Maximum activity was observed at 88 degrees C and pH 6.5. The recombinant trehalase exhibited a K(m) of 0.16 mM and a V(max) of 81 micromol of trehalose (min)(-1) (mg of protein)(-1) at the optimal temperature for growth of R. marinus (65 degrees C) and pH 6.5. The enzyme was highly specific for trehalose and was inhibited by glucose with a K(i) of 7 mM. This is the most thermostable trehalase ever characterized. Moreover, this is the first report on the identification and characterization of a trehalase from a thermophilic bacterium.