Accumulation of Mannosylglycerate and Di-myo-Inositol-Phosphate by Pyrococcus furiosus in Response to Salinity and Temperature

The Mystery of Piezophiles: Understudied Microorganisms from the Deep, Dark Subsurface

Microorganisms that can withstand high pressure within an environment are termed piezophiles. These organisms are considered extremophiles and inhabit the deep marine or terrestrial subsurface. Because these microorganisms are not easily accessed and require expensive sampling methods and laboratory instruments, advancements in this field have been limited compared to other extremophiles. This review summarizes the current knowledge on piezophiles, notably the cellular and physiological adaptations that such microorganisms possess to withstand and grow in high-pressure environments. Based on existing studies, organisms from both the deep marine and terrestrial subsurface show similar adaptations to high pressure, including increased motility, an increase of unsaturated bonds within the cell membrane lipids, upregulation of heat shock proteins, and differential gene-regulation systems. Notably, more adaptations have been identified within the deep marine subsurface organisms due to the relative paucity of studies performed on deep terrestrial subsurface environments. Nevertheless, similar adaptations have been found within piezophiles from both systems, and therefore the microbial biogeography concepts used to assess microbial dispersal and explore if similar organisms can be found throughout deep terrestrial environments are also briefly discussed.

Carnitine is a pharmacological allosteric chaperone of the human lysosomal α-glucosidase

Pompe disease is an inherited metabolic disorder due to the deficiency of the lysosomal acid α-glucosidase (GAA). The only approved treatment is enzyme replacement therapy with the recombinant enzyme (rhGAA). Further approaches like pharmacological chaperone therapy, based on the stabilising effect induced by small molecules on the target enzyme, could be a promising strategy. However, most known chaperones could be limited by their potential inhibitory effects on patient's enzymes. Here we report on the discovery of novel chaperones for rhGAA, L- and D-carnitine, and the related compound acetyl-D-carnitine. These drugs stabilise the enzyme at pH and temperature without inhibiting the activity and acted synergistically with active-site directed pharmacological chaperones. Remarkably, they enhanced by 4-fold the acid α-glucosidase activity in fibroblasts from three Pompe patients with added rhGAA. This synergistic effect of L-carnitine and rhGAA has the potential to be translated into improved therapeutic efficacy of ERT in Pompe disease.

Characterization and adaptation of Caldicellulosiruptor strains to higher sugar concentrations, targeting enhanced hydrogen production from lignocellulosic hydrolysates

BACKGROUND

The members of the genus Caldicellulosiruptor have the potential for future integration into a biorefinery system due to their capacity to generate hydrogen close to the theoretical limit of 4 mol H₂/mol hexose, use a wide range of sugars and can grow on numerous lignocellulose hydrolysates. However, members of this genus are unable to survive in high sugar concentrations, limiting their ability to grow on more concentrated hydrolysates, thus impeding their industrial applicability. In this study five members of this genus, C. owensensis, C. kronotskyensis, C. bescii, C. acetigenus and C. kristjanssonii, were developed to tolerate higher sugar concentrations through an adaptive laboratory evolution (ALE) process. The developed mixed population C. owensensis CO80 was further studied and accompanied by the development of a kinetic model based on Monod kinetics to quantitatively compare it with the parental strain.

RESULTS

Mixed populations of Caldicellulosiruptor tolerant to higher glucose concentrations were obtained with C. owensensis adapted to grow up to 80 g/L glucose; other strains in particular C. kristjanssonii demonstrated a greater restriction to adaptation. The C. owensensis CO80 mixed population was further studied and demonstrated the ability to grow in glucose concentrations up to 80 g/L glucose, but with reduced volumetric hydrogen productivities ([Formula: see text]) and incomplete sugar conversion at elevated glucose concentrations. In addition, the carbon yield decreased with elevated concentrations of glucose. The ability of the mixed population C. owensensis CO80 to grow in high glucose concentrations was further described with a kinetic growth model, which revealed that the critical sugar concentration of the cells increased fourfold when cultivated at higher concentrations. When co-cultured with the adapted C. saccharolyticus G5 mixed culture at a hydraulic retention time (HRT) of 20 h, C. owensensis constituted only 0.09-1.58% of the population in suspension.

CONCLUSIONS

The adaptation of members of the Caldicellulosiruptor genus to higher sugar concentrations established that the ability to develop improved strains via ALE is species dependent, with C. owensensis adapted to grow on 80 g/L, whereas C. kristjanssonii could only be adapted to 30 g/L glucose. Although C. owensensis CO80 was adapted to a higher sugar concentration, this mixed population demonstrated reduced [Formula: see text] with elevated glucose concentrations. This would indicate that while ALE permits adaptation to elevated sugar concentrations, this approach does not result in improved fermentation performances at these higher sugar concentrations. Moreover, the observation that planktonic mixed culture of CO80 was outcompeted by an adapted C. saccharolyticus, when co-cultivated in continuous mode, indicates that the robustness of CO80 mixed culture should be improved for industrial application.

The biology of thermoacidophilic archaea from the order Sulfolobales

Thermoacidophilic archaea belonging to the order Sulfolobales thrive in extreme biotopes, such as sulfuric hot springs and ore deposits. These microorganisms have been model systems for understanding life in extreme environments, as well as for probing the evolution of both molecular genetic processes and central metabolic pathways. Thermoacidophiles, such as the Sulfolobales, use typical microbial responses to persist in hot acid (e.g. motility, stress response, biofilm formation), albeit with some unusual twists. They also exhibit unique physiological features, including iron and sulfur chemolithoautotrophy, that differentiate them from much of the microbial world. Although first discovered >50 years ago, it was not until recently that genome sequence data and facile genetic tools have been developed for species in the Sulfolobales. These advances have not only opened up ways to further probe novel features of these microbes but also paved the way for their potential biotechnological applications. Discussed here are the nuances of the thermoacidophilic lifestyle of the Sulfolobales, including their evolutionary placement, cell biology, survival strategies, genetic tools, metabolic processes and physiological attributes together with how these characteristics make thermoacidophiles ideal platforms for specialized industrial processes.

Salt Stress Response of Sulfolobus acidocaldarius Involves Complex Trehalose Metabolism Utilizing a Novel Trehalose-6-Phosphate Synthase (TPS)/Trehalose-6-Phosphate Phosphatase (TPP) Pathway

The crenarchaeon Sulfolobus acidocaldarius has been described to synthesize trehalose via the maltooligosyltrehalose synthase (TreY) and maltooligosyltrehalose trehalohydrolase (TreZ) pathway, and the trehalose glycosyltransferring synthase (TreT) pathway has been predicted. Deletion mutant analysis of strains with single and double deletions of ΔtreY and ΔtreT in S. acidocaldarius revealed that in addition to these two pathways, a third, novel trehalose biosynthesis pathway is operative in vivo: the trehalose-6-phosphate (T6P) synthase/T6P phosphatase (TPS/TPP) pathway. In contrast to known TPS proteins, which belong to the GT20 family, the S. acidocaldarius TPS belongs to the GT4 family, establishing a new function within this group of enzymes. This novel GT4-like TPS was found to be present mainly in the Sulfolobales The ΔtreY ΔtreT Δtps triple mutant of S. acidocaldarius, which lacks the ability to synthesize trehalose, showed no altered phenotype under standard conditions or heat stress but was unable to grow under salt stress. Accordingly, in the wild-type strain, a significant increase of intracellular trehalose formation was observed under salt stress. Quantitative real-time PCR showed a salt stress-mediated induction of all three trehalose-synthesizing pathways. This demonstrates that in Archaea, trehalose plays an essential role for growth under high-salt conditions.IMPORTANCE The metabolism and function of trehalose as a compatible solute in Archaea was not well understood. This combined genetic and enzymatic approach at the interface of microbiology, physiology, and microbial ecology gives important insights into survival under stress, adaptation to extreme environments, and the role of compatible solutes in Archaea Here, we unraveled the complexity of trehalose metabolism, and we present a comprehensive study on trehalose function in stress response in S. acidocaldarius This sheds light on the general microbiology and the fascinating metabolic repertoire of Archaea, involving many novel biocatalysts, such as glycosyltransferases, with great potential in biotechnology.

Exploiting the rationale behind substrate recognition by promiscuous thermophilic NDP-sugar pyrophosphorylase for expanding glycorandomization: an in silico study

The fundamental substrates for protein glycosylation are provided by a group of enzymes known as NDP-sugar pyrophosphorylases (NSPases) which utilize nucleotide triphosphate (NTP) and sugar 1-phosphate to catalyze the formation of nucleotide diphospho-sugar (NDP-sugar). The promiscuous nature of NSPases is often exploited during chemoenzymatic glycorandomization in the pursuit of novel therapeutics. However, till date, the number of inherently promiscuous NSPases reported and the rationale behind their promiscuity is meager. In this study, we have identified a set of NSPases from a hyperthermophilic archaeon Pyrococcus horikoshii OT3 to identify probable candidates for glycorandomization. We identified a set of NSPases that include both substrate-specific and substrate-promiscuous NSPases with a visible predominance of the latter group. The rationale behind the promiscuity (or specificity) vividly lies in the repertoire of amino acid residues that assemble the active site for recognition of the substrate moiety. Furthermore, the absence of a function-specific auxiliary domain promotes substrate promiscuity in NSPases. This study, thus, provides a novel set of thermophilic NSPases that can be employed for chemoenzymatic glycorandomization. More importantly, identification of the residues that render substrate promiscuity (or specificity) would assist in sequence-based rational engineering of NSPases for enhanced glycorandomization. Communicated by Ramaswamy H. Sarma.

Trehalose-6-phosphate-mediated phenotypic change in Acinetobacter baumannii

The stress protectant trehalose is synthesized in Acinetobacter baumannii from UPD-glucose and glucose-6-phosphase via the OtsA/OtsB pathway. Previous studies proved that deletion of otsB led to a decreased virulence, the inability to grow at 45°C and a slight reduction of growth at high salinities indicating that trehalose is the cause of these phenotypes. We have questioned this conclusion by producing ∆otsA and ∆otsBA mutants and studying their phenotypes. Only deletion of otsB, but not deletion of otsA or otsBA, led to growth impairments at high salt and high temperature. The intracellular concentrations of trehalose and trehalose-6-phosphate were measured by NMR or enzymatic assay. Interestingly, none of the mutants accumulated trehalose any more but the ∆otsB mutant with its defect in trehalose-6-phosphate phosphatase activity accumulated trehalose-6-phosphate. Moreover, expression of otsA in a ∆otsB background under conditions where trehalose synthesis is not induced led to growth inhibition and the accumulation of trehalose-6-phosphate. Our results demonstrate that trehalose-6-phosphate affects multiple physiological activities in A. baumannii ATCC 19606.

Random mutagenesis of a hyperthermophilic archaeon identified tRNA modifications associated with cellular hyperthermotolerance

Random mutagenesis for the hyperthermophilic archaeon Thermococcus kodakarensis was established by the insertion of an artificial transposon designed to allow easy identification of the transposon-inserted locus. The phenotypic screening was applied for the isolation of thermosensitive mutants of T. kodakarensis, which resulted in the isolation of 16 mutants showing defective growth at the supraoptimal temperature 93°C. The high occurrence of the mutants suggested that the high thermotolerance of hyperthermophiles was achieved by a combination of diverse gene functions. The transposon insertion sites in two-thirds of the mutants were identified in a group of genes responsible for tRNA modifications including 7-formamidino-7-deaza-guanosine (archaeosine), N¹-methyladenosine/N¹-methylinosine, N⁴-acetylcytidine, and N²-dimethylguanosine/N²,N²-dimethylguanosine. LC–MS/MS analyses of tRNA nucleosides and fragments exhibited disappearance of the corresponding modifications in the mutants. The melting temperature of total tRNA fraction isolated from the mutants lacking archaeosine or N¹-methyladenosine/N¹-methylinosine decreased significantly, suggesting that the thermosensitive phenotype of these mutants was attributed to low stability of the hypomodified tRNAs. Genes for metabolism, transporters, and hypothetical proteins were also identified in the thermosensitive mutants. The present results demonstrated the usefulness of random mutagenesis for the studies on the hyperthermophile, as well as crucial roles of tRNA modifications in cellular thermotolerance.

Combined transcriptomics-metabolomics profiling of the heat shock response in the hyperthermophilic archaeon Pyrococcus furiosus

Pyrococcus furiosus is a remarkable archaeon able to grow at temperatures around 100 °C. To gain insight into how this model hyperthermophile copes with heat stress, we compared transcriptomic and metabolomic data of cells subjected to a temperature shift from 90 °C to 97 °C. In this study, we used RNA-sequencing to characterize the global variation in gene expression levels, while nuclear magnetic resonance (NMR) and targeted ion exchange liquid chromatography-mass spectrometry (LC-MS) were used to determine changes in metabolite levels. Of the 552 differentially expressed genes in response to heat shock conditions, 257 were upregulated and 295 were downregulated. In particular, there was a significant downregulation of genes for synthesis and transport of amino acids. At the metabolite level, 37 compounds were quantified. The level of di-myo-inositol phosphate, a canonical heat stress solute among marine hyperthermophiles, increased considerably (5.4-fold) at elevated temperature. Also, the levels of mannosylglycerate, UDP-N-acetylglucosamine (UDPGlcNac) and UDP-N-acetylgalactosamine were enhanced. The increase in the pool of UDPGlcNac was concurrent with an increase in the transcript levels of the respective biosynthetic genes. This work provides the first metabolomic analysis of the heat shock response of a hyperthermophile.

Glycine Betaine Monooxygenase, an Unusual Rieske-Type Oxygenase System, Catalyzes the Oxidative N-Demethylation of Glycine Betaine in Chromohalobacter salexigens DSM 3043

Although some bacteria, including Chromohalobacter salexigens DSM 3043, can use glycine betaine (GB) as a sole source of carbon and energy, little information is available about the genes and their encoded proteins involved in the initial step of the GB degradation pathway. In the present study, the results of conserved domain analysis, construction of in-frame deletion mutants, and an in vivo functional complementation assay suggested that the open reading frames Csal_1004 and Csal_1005, designated bmoA and bmoB, respectively, may act as the terminal oxygenase and the ferredoxin reductase genes in a novel Rieske-type oxygenase system to convert GB to dimethylglycine in C. salexigens DSM 3043. To further verify their function, BmoA and BmoB were heterologously overexpressed in Escherichia coli, and ¹³C nuclear magnetic resonance analysis revealed that dimethylglycine was accumulated in E. coli BL21(DE3) expressing BmoAB or BmoA. In addition, His-tagged BmoA and BmoB were individually purified to electrophoretic homogeneity and estimated to be a homotrimer and a monomer, respectively. In vitro biochemical analysis indicated that BmoB is an NADH-dependent flavin reductase with one noncovalently bound flavin adenine dinucleotide (FAD) as its prosthetic group. In the presence of BmoB, NADH, and flavin, BmoA could aerobically degrade GB to dimethylglycine with the concomitant production of formaldehyde. BmoA exhibited strict substrate specificity for GB, and its demethylation activity was stimulated by Fe²⁺ Phylogenetic analysis showed that BmoA belongs to group V of the Rieske nonheme iron oxygenase (RO) family, and all the members in this group were able to use quaternary ammonium compounds as substrates.IMPORTANCE GB is widely distributed in nature. In addition to being accumulated intracellularly as a compatible solute to deal with osmotic stress, it can be utilized by many bacteria as a source of carbon and energy. However, very limited knowledge is presently available about the molecular and biochemical mechanisms for the initial step of the aerobic GB degradation pathway in bacteria. Here, we report the molecular and biochemical characterization of a novel two-component Rieske-type monooxygenase system, GB monooxygenase (BMO), which is responsible for oxidative demethylation of GB to dimethylglycine in C. salexigens DSM 3043. The results gained in this study extend our knowledge on the catalytic reaction of microbial GB degradation to dimethylglycine.

Trehalose, a temperature- and salt-induced solute with implications in pathobiology of Acinetobacter baumannii

Acinetobacter baumannii is an opportunistic human pathogen that has become a global threat to healthcare institutions worldwide. A major factor contributing to success of this bacterium is its outstanding ability to survive on dry surfaces. The molecular basis for desiccation resistance is not completely understood. This study focused on growth under osmotic stress and aimed to identify the pool of compatible solutes synthesized in response to these low water activity conditions. A. baumannii produced mannitol as compatible solute, but in contrast to Acinetobacter baylyi, also trehalose was accumulated in response to increasing NaCl concentrations. The genome of A. baumannii encodes a trehalose-6-phosphate phosphatase (OtsB) and a trehalose-6-phosphate synthase (OtsA). Deletion of otsB abolished trehalose formation, demonstrating that otsB is essential for trehalose biosynthesis. Growth of the mutant was neither impaired at low salt nor at 500 mM NaCl, but it did not grow at high temperatures, indicating a dual function of trehalose in osmo- and thermoprotection. This led us to analyse temperature dependence of trehalose formation. Indeed, expression of otsB was not only induced by high osmolarity but also by high temperature. Concurrently, trehalose was accumulated in cells grown at high temperature. Taken together, these data point to an important role of trehalose in A. baumannii beyond osmoprotection.

Influence of osmotic stress on desiccation and irradiation tolerance of (hyper)-thermophilic microorganisms

This study examined the influence of prior salt adaptation on the survival rate of (hyper)-thermophilic bacteria and archaea after desiccation and UV or ionizing irradiation treatment. Survival rates after desiccation of Hydrogenothermus marinus and Archaeoglobus fulgidus increased considerably when the cells were cultivated at higher salt concentrations before drying. By doubling the concentration of NaCl, a 30 times higher survival rate of H. marinus after desiccation was observed. Under salt stress, the compatible solute diglycerol phosphate in A. fulgidus and glucosylglycerate in H. marinus accumulated in the cytoplasm. Several different compatible solutes were added as protectants to A. fulgidus and H. marinus before desiccation treatment. Some of these had similar effects as intracellularly produced compatible solutes. The survival rates of H. marinus and A. fulgidus after exposure to UV-C (254 nm) or ionizing X-ray/gamma radiation were irrespective of the salt-induced synthesis or the addition of compatible solutes.

Molecular chaperone accumulation as a function of stress evidences adaptation to high hydrostatic pressure in the piezophilic archaeon Thermococcus barophilus

The accumulation of mannosyl-glycerate (MG), the salinity stress response osmolyte of Thermococcales, was investigated as a function of hydrostatic pressure in Thermococcus barophilus strain MP, a hyperthermophilic, piezophilic archaeon isolated from the Snake Pit site (MAR), which grows optimally at 40 MPa. Strain MP accumulated MG primarily in response to salinity stress, but in contrast to other Thermococcales, MG was also accumulated in response to thermal stress. MG accumulation peaked for combined stresses. The accumulation of MG was drastically increased under sub-optimal hydrostatic pressure conditions, demonstrating that low pressure is perceived as a stress in this piezophile, and that the proteome of T. barophilus is low-pressure sensitive. MG accumulation was strongly reduced under supra-optimal pressure conditions clearly demonstrating the structural adaptation of this proteome to high hydrostatic pressure. The lack of MG synthesis only slightly altered the growth characteristics of two different MG synthesis deletion mutants. No shift to other osmolytes was observed. Altogether our observations suggest that the salinity stress response in T. barophilus is not essential and may be under negative selective pressure, similarly to what has been observed for its thermal stress response.

Mannosylglycerate: structural analysis of biosynthesis and evolutionary history

Halophilic and halotolerant microorganisms adapted to thrive in hot environments accumulate compatible solutes that usually have a negative charge either associated with a carboxylic group or a phosphodiester unit. Mannosylglycerate (MG) has been detected in several members of (hyper)thermophilic bacteria and archaea, in which it responds primarily to osmotic stress. The outstanding ability of MG to stabilize protein structure in vitro as well as in vivo has been convincingly demonstrated. These findings led to an increasingly supported link between MG and microbial adaptation to high temperature. However, the accumulation of MG in many red algae has been known for a long time, and the peculiar distribution of MG in such distant lineages was intriguing. Knowledge on the biosynthetic machinery together with the rapid expansion of genome databases allowed for structural and phylogenetic analyses and provided insight into the distribution of MG. The two pathways for MG synthesis have distinct evolutionary histories and physiological roles: in red algae MG is synthesised exclusively via the single-step pathway and most probably is unrelated with stress protection. In contrast, the two-step pathway is strongly associated with osmoadaptation in (hyper)thermophilic prokaryotes. The phylogenetic analysis of the two-step pathway also reveals a second cluster composed of fungi and mesophilic bacteria, but MG has not been demonstrated in members of this cluster; we propose that the synthase is part of a more complex pathway directed at the synthesis of yet unknown molecules containing the mannosyl-glyceryl unit.

Structural basis for catalysis in a CDP-alcohol phosphotransferase

The CDP-alcohol phosphotransferase (CDP-AP) family of integral membrane enzymes catalyses the transfer of a substituted phosphate group from a CDP-linked donor to an alcohol acceptor. This is an essential reaction for phospholipid biosynthesis across all kingdoms of life, and it is catalysed solely by CDP-APs. Here we report the 2.0 Å resolution crystal structure of a representative CDP-AP from Archaeoglobus fulgidus. The enzyme (AF2299) is a homodimer, with each protomer consisting of six transmembrane helices and an N-terminal cytosolic domain. A polar cavity within the membrane accommodates the active site, lined with the residues from an absolutely conserved CDP-AP signature motif (D(1)xxD(2)G(1)xxAR...G(2)xxxD(3)xxxD(4)). Structures in the apo, CMP-bound, CDP-bound and CDP-glycerol-bound states define functional roles for each of these eight conserved residues and allow us to propose a sequential, base-catalysed mechanism universal for CDP-APs, in which the fourth aspartate (D4) acts as the catalytic base.

Mannosylglycerate and di-myo-inositol phosphate have interchangeable roles during adaptation of Pyrococcus furiosus to heat stress

Marine hyperthermophiles accumulate small organic compounds, known as compatible solutes, in response to supraoptimal temperatures or salinities. Pyrococcus furiosus is a hyperthermophilic archaeon that grows optimally at temperatures near 100°C. This organism accumulates mannosylglycerate (MG) and di-myo-inositol phosphate (DIP) in response to osmotic and heat stress, respectively. It has been assumed that MG and DIP are involved in cell protection; however, firm evidence for the roles of these solutes in stress adaptation is still missing, largely due to the lack of genetic tools to produce suitable mutants of hyperthermophiles. Recently, such tools were developed for P. furiosus, making this organism an ideal target for that purpose. In this work, genes coding for the synthases in the biosynthetic pathways of MG and DIP were deleted by double-crossover homologous recombination. The growth profiles and solute patterns of the two mutants and the parent strain were investigated under optimal growth conditions and also at supraoptimal temperatures and NaCl concentrations. DIP was a suitable replacement for MG during heat stress, but substitution of MG for DIP and aspartate led to less efficient growth under conditions of osmotic stress. The results suggest that the cascade of molecular events leading to MG synthesis is tuned for osmotic adjustment, while the machinery for induction of DIP synthesis responds to either stress agent. MG protects cells against heat as effectively as DIP, despite the finding that the amount of DIP consistently increases in response to heat stress in the nine (hyper)thermophiles examined thus far.

Proteomic analysis of cross protection provided between cold and osmotic stress in Listeria monocytogenes

Listeria monocytogenes is a Gram-positive, foodborne pathogen responsible for approximately 28% of all food-related deaths each year in the United States. L. monocytogenes infections are linked to the consumption of minimally processed ready-to-eat (RTE) products such as cheese, deli meats, and cold-smoked finfish products. L. monocytogenes is resistant to stresses commonly encountered in the food-processing environment, including low pH, high salinity, oxygen content, and various temperatures. The purpose of this study was to determine if cells habituated at low temperatures would result in cross-protective effects against osmotic stress. We found that cells exposed to refrigerated temperatures prior to a mild salt stress treatment had increased survival in NaCl concentrations of 3%. Additionally, the longer the cells were pre-exposed to cold temperatures, the greater the increase in survival in 3% NaCl. A proteomics analysis was performed in triplicate in order to elucidate mechanisms involved in cold-stress induced cross protection against osmotic stress. Proteins involved in maintenance of the cell wall and cellular processes, such as penicillin binding proteins and osmolyte transporters, and processes involving amino acid metabolism, such as osmolyte synthesis, transport, and lipid biosynthesis, had the greatest increase in expression when cells were exposed to cold temperatures prior to salt. By gaining a better understanding of how this pathogen adapts physiologically to various environmental conditions, improvements can be made in detection and mitigation strategies.

Mannitol, a compatible solute synthesized by Acinetobacter baylyi in a two-step pathway including a salt-induced and salt-dependent mannitol-1-phosphate dehydrogenase

The nutritionally versatile and naturally competent soil bacterium Acinetobacter baylyi copes with salt stress by the accumulation of compatible solutes. NMR analyses revealed that cells amassed glutamate and the rather unusual sugar alcohol mannitol upon an increase of the external NaCl concentration. To unravel the path of mannitol biosynthesis, the genome was inspected for genes potentially involved in its biosynthesis. A gene encoding a potential mannitol-1-phosphate dehydrogenase (mtlD) was identified in the genome of A. baylyi. Expression of mtlD was highly induced at high salinity. mtlD was overexpressed and the purified protein indeed produced mannitol-1-phosphate from fructose-6-phosphate. The enzyme preferred NADPH over NADH and the specific activity of fructose-6-phosphate reduction with NADPH was 130 U mg(-1) . Enzymatic activity was strictly salt-dependent. Deletion of mtlD resulted in a complete loss of salt-dependent mannitol biosynthesis. We provide clear evidence that osmo-induced synthesis of the compatible solute mannitol is by a two-step pathway and that the mannitol-1-phosphate dehydrogenase mediating the first step of this pathway is regulated by salinity on the transcriptional as well as on the activity level.

Metabolic fingerprinting of the responses to salinity in the invasive ground beetle Merizodus soledadinus at the Kerguelen Islands

Salinity is an abiotic factor that may impact survival and fitness of terrestrial insects in coastal environments. Meanwhile, some terrestrial arthropods can survive in hypersaline environments, and counterbalance osmotic stress by intra- and extracellular buildups of organic osmolytes. The ground beetle Merizodus soledadinus originates from South America and it is distributed in forests and riparian zones, where salinity levels are considerably low. This species has been introduced at the Kerguelen Islands a century ago, where it colonized coastal areas (tide drift lines), and must thus withstand salinity variations due to tide, spray, and organic matter deposited therein. In the present study, we addressed the physiological plasticity of M. soledadinus to saline conditions, by monitoring body water content and survival in adults experimentally subjected to different salinities. We also investigated possible metabolic adjustments involved at three contrasted salinity levels (0‰, 35‰, 70‰) at 4 and 8°C. We hypothesized that this invasive ground beetle can withstand a broad range of salinity conditions thanks to the plastic accumulation of compatible solutes. The study revealed a progressive drop in body water content in individuals exposed to 35‰ and 70‰, as opposed to the controls. Metabolic fingerprints showed compatible solute (erythritol, alanine, glycine and proline) accumulation at medium and high salinity conditions (35‰ and 70‰). We concluded that the osmo-induced accumulation of amino acids and polyols was likely to modulate the ground beetles' body water balance on medium saline substrates, thus enhancing their survival ability.

Role of Mn2+ and compatible solutes in the radiation resistance of thermophilic bacteria and archaea

Radiation-resistant bacteria have garnered a great deal of attention from scientists seeking to expose the mechanisms underlying their incredible survival abilities. Recent analyses showed that the resistance to ionizing radiation (IR) in the archaeon Halobacterium salinarum is dependent upon Mn-antioxidant complexes responsible for the scavenging of reactive oxygen species (ROS) generated by radiation. Here we examined the role of the compatible solutes trehalose, mannosylglycerate, and di-myo-inositol phosphate in the radiation resistance of aerobic and anaerobic thermophiles. We found that the IR resistance of the thermophilic bacteria Rubrobacter xylanophilus and Rubrobacter radiotolerans was highly correlated to the accumulation of high intracellular concentration of trehalose in association with Mn, supporting the model of Mn²⁺-dependent ROS scavenging in the aerobes. In contrast, the hyperthermophilic archaea Thermococcus gammatolerans and Pyrococcus furiosus did not contain significant amounts of intracellular Mn, and we found no significant antioxidant activity from mannosylglycerate and di-myo-inositol phosphate in vitro. We therefore propose that the low levels of IR-generated ROS under anaerobic conditions combined with highly constitutively expressed detoxification systems in these anaerobes are key to their radiation resistance and circumvent the need for the accumulation of Mn-antioxidant complexes in the cell.

Salt adaptation in Acinetobacter baylyi: identification and characterization of a secondary glycine betaine transporter

Members of the genus Acinetobacter are well known for their metabolic versatility that allows them to adapt to different ecological niches. Here, we have addressed how the model strain Acinetobacter baylyi copes with different salinities and low water activities. A. baylyi tolerates up to 900 mM sodium salts and even higher concentrations of potassium chloride. Growth at high salinities was better in complex than in mineral medium and addition of glycine betaine stimulated growth at high salinities in mineral medium. Cells grown at high salinities took up glycine betaine from the medium. Uptake of glycine betaine was energy dependent and dependent on a salinity gradient across the membrane. Inspection of the genome sequence revealed two potential candidates for glycine betaine transport, both encoding potential secondary transporters, one of the major facilitator superfamily (MFS) class (ACIAD2280) and one of the betaine/choline/carnitine transporter (BCCT) family (ACIAD3460). The latter is essential for glycine betaine transport in A. baylyi. The broad distribution of ACIAD3460 homologues indicates the essential role of secondary transporters in the adaptation of Acinetobacter species to osmotic stress.

Gluconeotrehalose is the principal organic solute in the psychrotolerant bacterium Carnobacterium strain 17-4

A high proportion of microorganisms that colonise cold environments originate from marine sites; hence, they must combine adaptation to low temperature with osmoregulation. However, little or nothing is known about the nature of compatible solutes used by cold-adapted organisms to balance the osmotic pressure of the external medium. We studied the intracellular accumulation of small organic solutes in the Arctic isolate Carnobacterium strain 17-4 as a function of the growth temperature and the NaCl concentration in the medium. Data on 16S rDNA sequence and DNA-DNA hybridisation tests corroborate the assignment of this isolate as a new species of the bacterial genus Carnobacterium. The growth profiles displayed maximal specific growth rate at 30°C in medium without NaCl, and maximal values of final biomass at growth temperatures between 10 and 20°C. Therefore, Carnobacterium strain 17-4 exhibits halotolerant and psychrotolerant behaviours. The solute pool contained glycine-betaine, the main solute used for osmoregulation, and an unknown compound whose structure was identified as α-glucopyranosyl-(1-3)-β-glucopyranosyl-(1-1)-α-glucopyranose (abbreviated as gluconeotrehalose), using nuclear magnetic resonance and mass spectrometry. This unusual solute consistently accumulated to high levels (0.35 ± 0.05 mg/mg cell protein) regardless of the growth temperature or salinity. The efficiency of gluconeotrehalose in the stabilisation of four model enzymes against heat damage was also assessed, and the effects were highly protein dependent. The lack of variation in the gluconeotrehalose content observed under heat stress, osmotic stress, and starvation provides no clue for the physiological role of this rare solute.

Diversity, biological roles and biosynthetic pathways for sugar-glycerate containing compatible solutes in bacteria and archaea

A decade ago the compatible solutes mannosylglycerate (MG) and glucosylglycerate (GG) were considered to be rare in nature. Apart from two species of thermophilic bacteria, Thermus thermophilus and Rhodothermus marinus, and a restricted group of hyperthermophilic archaea, the Thermococcales, MG had only been identified in a few red algae. Glucosylglycerate was considered to be even rarer and had only been detected as an insignificant solute in two halophilic microorganisms, a cyanobacterium, as a component of a polysaccharide and of a glycolipid in two actinobacteria. Unlike the hyper/thermophilic MG-accumulating microorganisms, branching close to the root of the Tree of Life, those harbouring GG shared a mesophilic lifestyle. Exceptionally, the thermophilic bacterium Persephonella marina was reported to accumulate GG. However, and especially owing to the identification of the key-genes for MG and GG synthesis and to the escalating numbers of genomes available, a plethora of new organisms with the resources to synthesize these solutes has been recognized. The accumulation of GG as an 'emergency' compatible solute under combined salt stress and nitrogen-deficient conditions now seems to be a disseminated survival strategy from enterobacteria to marine cyanobacteria. In contrast, the thermophilic and extremely radiation-resistant bacterium Rubrobacter xylanophilus is the only actinobacterium known to accumulate MG, and under all growth conditions tested. This review addresses the environmental factors underlying the accumulation of MG, GG and derivatives in bacteria and archaea and their roles during stress adaptation or as precursors for more elaborated macromolecules. The diversity of pathways for MG and GG synthesis as well as those for some of their derivatives is also discussed. The importance of glycerate-derived organic solutes in the microbial world is only now being recognized. Their stress-dependent accumulation and the molecular aspects of their interactions with biomolecules have already fuelled several emerging applications in biotechnology and biomedicine.

Are compatible solutes compatible with biological treatment of saline wastewater? Batch and continuous studies using submerged anaerobic membrane bioreactors (SAMBRs)

This study investigated fundamental mechanisms that anaerobic biomass employ to cope with salinity, and applied these findings to a continuous SAMBR. When anaerobic biomass was exposed to 20 and 40 g NaCl/L for 96 h, the main solute generated de novo by biomass was trehalose. When we separately introduced trehalose, N-acetyl-β-lysine and potassium into a batch culture a slight decrease in sodium inhibition was observed. In contrast, the addition of 0.1 mM and 1 mM of glycine betaine dramatically improved the adaptation of anaerobic biomass to 35 g NaCl/L, and it continued to enhance the adaptation of biomass to the salt for the next three batch feedings without further addition. No shift in archaeal microbial diversity was found when anaerobic biomass was exposed in batch mode to 35 g NaCl/L for 360 h, and no changes were found when glycine betaine was added. The dominant species identified under these conditions were Methanosarcina mazeii and Methanosaeta sp. The addition of 5 mM glycine betaine to a continuous SAMBR at 12 h hydraulic retention time (HRT), and operation in batch mode for 2 days can significantly enhance saline (35 g NaCl/L) synthetic sewage degradation. In addition, the injection of 1 mM of glycine betaine into a SAMBR for five subsequent days also significantly enhanced dissolved organic carbon (DOC) removal from sewage under these conditions. The main compatible solutes generated by anaerobic biomass after 44 days exposure to 35 g NaCl/L in a SAMBR were N-acetyl-β-lysine and glycine betaine. Finally, the addition of 1 mM glycine betaine to the medium was beneficial for anaerobic biomass in batch mode at 20 °C under saline and non saline conditions.

Organic solutes in hyperthermophilic archaea

We examined the accumulation of organic solutes under optimum growth conditions in 12 species of thermophilic and hyperthermophilic Archaea belonging to the Crenarchaeota and Euryarchaeota. Pyrobaculum aerophilum, Thermoproteus tenax, Thermoplasma acidophilum, and members of the order Sulfolobales accumulated trehalose. Pyrococcus furiosus accumulated di-myo-inositol-1,1(prm1)(3,3(prm1))-phosphate and (beta)-mannosylglycerate, Methanothermus fervidus accumulated cyclic-2,3-bisphosphoglycerate and (beta)-mannosylglycerate, while the only solute detected in Pyrodictium occultum was di-myo-inositol-1,1(prm1)(3,3(prm1))-phosphate. Methanopyrus kandleri accumulated large concentrations of cyclic-2,3-bisphosphoglycerate. On the other hand, Archaeoglobus fulgidus accumulated three phosphorylated solutes; prominent among them was a compound identified as di-glycerol-phosphate. This solute increased in concentration as the salinity of the medium and the growth temperature were raised, suggesting that this compound serves as a general stress solute. Di-myo-inositol-1,1(prm1)(3,3(prm1))-phosphate accumulated at supraoptimal temperature only. The relationship between the accumulation of unusual solutes and high temperatures is also discussed.

Characterization of Di-myo-Inositol-1,1(prm1)-Phosphate in the Hyperthermophilic Bacterium Thermotoga maritima

Di-myo-inositol-1,1(prm1)-phosphate (DIP) is present at a significant concentration ((symbl)160 nmol/mg of protein) in the cytoplasm of the hyperthermophilic bacterium Thermotoga maritima. The concentration of DIP was independent of the pH of the growth medium or the cell growth phase but increased with increasing concentrations of NaCl in the growth medium, reaching a maximum ((symbl)450 nmol/mg of protein) at 0.4 to 0.6 M NaCl. A large-scale purification procedure for DIP which yields approximately 18 g of DIP per kg of cells (wet weight) is described. Purified DIP was stable at 90(deg)C for at least 5 h. The presence of DIP (50 mM) did not increase the stability at 90(deg)C of pure forms of the hydrogenase or pyruvate ferredoxin oxidoreductase of T. maritima, suggesting that DIP is not a general thermoprotectant.

Acquired Thermotolerance and Stressed-Phase Growth of the Extremely Thermoacidophilic Archaeon Metallosphaera sedula in Continuous Culture

The response of an extremely thermoacidophilic archaeon, Metallosphaera sedula (growth temperature range, 50 to 79(deg)C; optimum temperature, 74(deg)C; optimum pH, 2.0), to thermal stress was investigated by using a 10-liter continuous cultivation system. M. sedula, growing at 74(deg)C, pH 2.0, and a dilution rate of 0.04 hr(sup-1), was subjected to both abrupt and gradual temperature shifts in continuous culture to determine the responses of cell density levels and protein synthesis patterns. An abrupt temperature shift from 74 to 79(deg)C resulted in little, if any, changes in cell density and a small increase in total protein per cell. When the culture temperature was shifted further to 80.5(deg)C, cell density dropped to below 5 x 10(sup6) cells/ml from 10(sup8) cells/ml, leading to washout of the culture. Operation at this temperature and slightly higher temperatures, however, could be achieved by exposing the culture to thermal stress more gradually (0.5(deg)C increments). As a result, stable operation could be maintained at temperatures of up to 81(deg)C, and the washout temperature could be increased to 82.5(deg)C. Continuous culture operation at 81(deg)C for 100 h (stressed phase) led to an approximately sevenfold lower steady-state cell density than that observed for operation at or below 79(deg)C. However, sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis (both one and two dimensional) revealed significantly higher levels (sixfold increase) of a 66-kDa stress response protein (MseHSP60), immunologically related to Thermophilic Factor 55 from Sulfolobus shibatae (J. D. Trent, J. Osipiuk, and T. Pinkau, J. Bacteriol. 172:1478-1484, 1990). If the acclimated culture was returned to a lower temperature (i.e., 74(deg)C), the amount of MseHSP60 returned to levels observed prior to thermal acclimation. Furthermore, when the previously acclimated culture (at 81(deg)C) was shifted back from 74 to 81(deg)C, without going through gradual acclimation steps, the result was the immediate onset of washout, suggesting no residual thermotolerance. This study shows that gradual thermal acclimation of M. sedula could only extend the temperature range of stable growth for this organism by 2(deg)C above its maximal growth temperature, albeit at reduced cell densities. Also, this investigation illustrates the utility of continuous culture for characterizing heat shock response and assessing maximum growth temperatures for extremely thermophilic microorganisms.

Molybdenum incorporation in tungsten aldehyde oxidoreductase enzymes from Pyrococcus furiosus

The hyperthermophilic archaeon Pyrococcus furiosus expresses five aldehyde oxidoreductase (AOR) enzymes, all containing a tungsto-bispterin cofactor. The growth of this organism is fully dependent on the presence of tungsten in the growth medium. Previous studies have suggested that molybdenum is not incorporated in the active site of these enzymes. Application of the radioisotope (99)Mo in metal isotope native radioautography in gel electrophoresis (MIRAGE) technology to P. furiosus shows that molybdenum can in fact be incorporated in all five AOR enzymes. Mo(V) signals characteristic for molybdopterin were observed in formaldehyde oxidoreductase (FOR) in electron paramagnetic resonance (EPR)-monitored redox titrations. Our finding that the aldehyde oxidation activity of FOR and WOR5 (W-containing oxidoreductase 5) correlates only with the residual tungsten content suggests that the Mo-containing AORs are most likely inactive. An observed W/Mo antagonism is indicative of tungstate-dependent negative feedback of the expression of the tungstate/molybdate ABC transporter. An intracellular selection mechanism for tungstate and molybdate processing has to be present, since tungsten was found to be preferentially incorporated into the AORs even under conditions with comparable intracellular concentrations of tungstate and molybdate. Under the employed growth conditions of starch as the main carbon source in a rich medium, no tungsten- and/or molybdenum-associated proteins are detected in P. furiosus other than the high-affinity transporter, the proteins of the metallopterin insertion machinery, and the five W-AORs.

Thermococcus kodakarensis mutants deficient in di-myo-inositol phosphate use aspartate to cope with heat stress

Many of the marine microorganisms which are adapted to grow at temperatures above 80 degrees C accumulate di-myo-inositol phosphate (DIP) in response to heat stress. This led to the hypothesis that the solute plays a role in thermoprotection, but there is a lack of definitive experimental evidence. Mutant strains of Thermococcus kodakarensis (formerly Thermococcus kodakaraensis), manipulated in their ability to synthesize DIP, were constructed and used to investigate the involvement of DIP in thermoadaptation of this archaeon. The solute pool of the parental strain comprised DIP, aspartate, and alpha-glutamate. Under heat stress the level of DIP increased 20-fold compared to optimal conditions, whereas the pool of aspartate increased 4.3-fold in response to osmotic stress. Deleting the gene encoding the key enzyme in DIP synthesis, CTP:inositol-1-phosphate cytidylyltransferase/CDP-inositol:inositol-1-phosphate transferase, abolished DIP synthesis. Conversely, overexpression of the same gene resulted in a mutant with restored ability to synthesize DIP. Despite the absence of DIP in the deletion mutant, this strain exhibited growth parameters similar to those of the parental strain, both at optimal (85 degrees C) and supraoptimal (93.7 degrees C) temperatures for growth. Analysis of the respective solute pools showed that DIP was replaced by aspartate. We conclude that DIP is part of the strategy used by T. kodakarensis to cope with heat stress, and aspartate can be used as an alternative solute of similar efficacy. This is the first study using mutants to demonstrate the involvement of compatible solutes in the thermoadaptation of (hyper)thermophilic organisms.

A unique beta-1,2-mannosyltransferase of Thermotoga maritima that uses di-myo-inositol phosphate as the mannosyl acceptor

In addition to di-myo-inositol-1,3'-phosphate (DIP), a compatible solute widespread in hyperthermophiles, the organic solute pool of Thermotoga maritima comprises 2-(O-beta-D-mannosyl)-di-myo-inositol-1,3'-phosphate (MDIP) and 2-(O-beta-D-mannosyl-1,2-O-beta-D-mannosyl)-di-myo-inositol-1,3'-phosphate (MMDIP), two newly identified beta-1,2-mannosides. In cells grown under heat stress, MDIP was the major solute, accounting for 43% of the total pool; MMDIP and DIP accumulated to similar levels, each corresponding to 11.5% of the total pool. The synthesis of MDIP involved the transfer of the mannosyl group from GDP-mannose to DIP in a single-step reaction catalyzed by MDIP synthase. This enzyme used MDIP as an acceptor of a second mannose residue, yielding the di-mannosylated compound. Minor amounts of the tri-mannosylated form were also detected. With a genomic approach, putative genes for MDIP synthase were identified in the genome of T. maritima, and the assignment was confirmed by functional expression in Escherichia coli. Genes with significant sequence identity were found only in the genomes of Thermotoga spp., Aquifex aeolicus, and Archaeoglobus profundus. MDIP synthase of T. maritima had maximal activity at 95 degrees C and apparent K(m) values of 16 mM and 0.7 mM for DIP and GDP-mannose, respectively. The stereochemistry of MDIP was characterized by isotopic labeling and nuclear magnetic resonance (NMR): DIP selectively labeled with carbon 13 at position C1 of the l-inositol moiety was synthesized and used as a substrate for MDIP synthase. This beta-1,2-mannosyltransferase is unrelated to known glycosyltransferases, and within the domain Bacteria, it is restricted to members of the two deepest lineages, i.e., the Thermotogales and the Aquificales. To our knowledge, this is the first beta-1,2-mannosyltransferase characterized thus far.

Asymmetric Syntheses of L,L- and L,D-di-myo-inositol-1,1'-phosphate and their behavior as stabilizers of enzyme activity at extreme temperatures

The big "DIP"per: The preparation of both l,l-DIP and l,d-DIP (see structures) involves a complex case of double asymmetric induction in the key step of the synthesis. The differential ability of each isomer to contribute to thermoprotection in the context of a key enzyme has been assessed and both isomers of DIP are shown to possess biological activity.

Design of new enzyme stabilizers inspired by glycosides of hyperthermophilic microorganisms

In response to stressful conditions like supra-optimal salinity in the growth medium or temperature, many microorganisms accumulate low-molecular-mass organic compounds known as compatible solutes. In contrast with mesophiles that accumulate neutral or zwitterionic compounds, the solutes of hyperthermophiles are typically negatively charged. (2R)-2-(alpha-D-Mannopyranosyl)glycerate (herein abbreviated as mannosylglycerate) is one of the most widespread solutes among thermophilic and hyperthermophilic prokaryotes. In this work, several molecules chemically related to mannosylglycerate were synthesized, namely (2S)-2-(1-O-alpha-D-mannopyranosyl)propionate, 2-(1-O-alpha-D-mannopyranosyl)acetate, (2R)-2-(1-O-alpha-D-glucopyranosyl)glycerate and 1-O-(2-glyceryl)-alpha-D-mannopyranoside. The effectiveness of the newly synthesized compounds for the protection of model enzymes against heat-induced denaturation, aggregation and inactivation was evaluated, using differential scanning calorimetry, light scattering and measurements of residual activity. For comparison, the protection induced by natural compatible solutes, either neutral (e.g., trehalose, glycerol, ectoine) or negatively charged (di-myo-inositol-1,3'-phosphate and diglycerol phosphate), was assessed. Phosphate, sulfate, acetate and KCl were also included in the assays to rank the solutes and new compounds in the Hofmeister series. The data demonstrate the superiority of charged organic solutes as thermo-stabilizers of enzymes and strongly support the view that the extent of protein stabilization rendered by those solutes depends clearly on the specific solute/enzyme examined. The relevance of these findings to our knowledge on the mode of action of charged solutes is discussed.

A novel trehalose synthesizing pathway in the hyperthermophilic Crenarchaeon Thermoproteus tenax: the unidirectional TreT pathway

In the genome of the hyperthermophilic archaeon Thermoproteus tenax a gene (treS/P) encoding a protein with similarity to annotated trehalose phosphorylase (TreP), trehalose synthase (TreS) and more recently characterized trehalose glycosyltransferring synthase (TreT) was identified. The treS/P gene as well as an upstream located ORF of unknown function (orfY) were cloned, heterologously expressed in E. coli and purified. The enzymatic characterization of the putative TreS/P revealed TreT activity. However, contrary to the previously characterized reversible TreT from Thermococcus litoralis and Pyrococcus horikoshii, the T. tenax enzyme is unidirectional and catalyzes only the formation of trehalose from UDP (ADP)-glucose and glucose. The T. tenax enzyme differs from the reversible TreT of T. litoralis by its preference for UDP-glucose as co-substrate. Phylogenetic and comparative gene context analyses reveal a conserved organization of the unidirectional TreT and OrfY gene cluster that is present in many Archaea and a few Bacteria. In contrast, the reversible TreT pathway seems to be restricted to only a few archaeal (e.g. Thermococcales) and bacterial (Thermotogales) members. Here we present a new pathway exclusively involved in trehalose synthesis--the unidirectional TreT pathway--and discuss its physiological role as well as its phylogenetic distribution.

Di-myo-inositol phosphate and novel UDP-sugars accumulate in the extreme hyperthermophile Pyrolobus fumarii

The archaeon Pyrolobus fumarii, one of the most extreme members of hyperthermophiles known thus far, is able to grow at temperatures up to 113 degrees C. Over a decade after the description of this organism our knowledge about the structures and strategies underlying its remarkable thermal resistance remains incipient. The accumulation of a restricted number of charged organic solutes is a common response to heat stress in hyperthermophilic organisms and accordingly their role in thermoprotection has been often postulated. In this work, the organic solute pool of P. fumarii was characterized using 1H, 13C, and 31P NMR. Di-myo-inositol phosphate was the major solute (0.21 micromol/mg protein), reinforcing the correlation between the occurrence of this solute and hyperthermophily; in addition, UDP-sugars (total concentration 0.11 micromol/mg protein) were present. The structures of the two major UDP-sugars were identified as UDP-alpha-GlcNAc3NAc and UDP-alpha-GlcNAc3NAc-(4<--1)-beta-GlcpNAc3NAc. Interestingly, the latter compound appears to be derived from the first one by addition of a 2,3-N-acetylglucoronic acid unit, suggesting that these UDP-sugars are intermediates of an N-linked glycosylation pathway. To our knowledge the UDP-disaccharide has not been reported elsewhere. The physiological roles of these organic solutes are discussed.

Small stress molecules inhibit aggregation and neurotoxicity of prion peptide 106-126

In prion diseases, the posttranslational modification of host-encoded prion protein PrP(c) yields a high beta-sheet content modified protein PrP(sc), which further polymerizes into amyloid fibrils. PrP106-126 initiates the conformational changes leading to the conversion of PrP(c) to PrP(sc). Molecules that can defunctionalize such peptides can serve as a potential tool in combating prion diseases. In microorganisms during stressed conditions, small stress molecules (SSMs) are formed to prevent protein denaturation and maintain protein stability and function. The effect of such SSMs on PrP106-126 amyloid formation is explored in the present study using turbidity, atomic force microscopy (AFM), and cellular toxicity assay. Turbidity and AFM studies clearly depict that the SSMs-ectoine and mannosylglyceramide (MGA) inhibit the PrP106-126 aggregation. Our study also connotes that ectoine and MGA offer strong resistance to prion peptide-induced toxicity in human neuroblastoma cells, concluding that such molecules can be potential inhibitors of prion aggregation and toxicity.

Bifunctional CTP:inositol-1-phosphate cytidylyltransferase/CDP-inositol:inositol-1-phosphate transferase, the key enzyme for di-myo-inositol-phosphate synthesis in several (hyper)thermophiles

The pathway for the synthesis of di-myo-inositol-phosphate (DIP) was recently elucidated on the basis of the detection of the relevant activities in cell extracts of Archaeoglobus fulgidus and structural characterization of products by nuclear magnetic resonance (NMR) (N. Borges, L. G. Gonçalves, M. V. Rodrigues, F. Siopa, R. Ventura, C. Maycock, P. Lamosa, and H. Santos, J. Bacteriol. 188:8128-8135, 2006). Here, a genomic approach was used to identify the genes involved in the synthesis of DIP. Cloning and expression in Escherichia coli of the putative genes for CTP:l-myo-inositol-1-phosphate cytidylyltransferase and DIPP (di-myo-inositol-1,3'-phosphate-1'-phosphate, a phosphorylated form of DIP) synthase from several (hyper)thermophiles (A. fulgidus, Pyrococcus furiosus, Thermococcus kodakaraensis, Aquifex aeolicus, and Rubrobacter xylanophilus) confirmed the presence of those activities in the gene products. The DIPP synthase activity was part of a bifunctional enzyme that catalyzed the condensation of CTP and l-myo-inositol-1-phosphate into CDP-l-myo-inositol, as well as the synthesis of DIPP from CDP-l-myo-inositol and l-myo-inositol-1-phosphate. The cytidylyltransferase was absolutely specific for CTP and l-myo-inositol-1-P; the DIPP synthase domain used only l-myo-inositol-1-phosphate as an alcohol acceptor, but CDP-glycerol, as well as CDP-l-myo-inositol and CDP-d-myo-inositol, were recognized as alcohol donors. Genome analysis showed homologous genes in all organisms known to accumulate DIP and for which genome sequences were available. In most cases, the two activities (l-myo-inositol-1-P cytidylyltransferase and DIPP synthase) were fused in a single gene product, but separate genes were predicted in Aeropyrum pernix, Thermotoga maritima, and Hyperthermus butylicus. Additionally, using l-myo-inositol-1-phosphate labeled on C-1 with carbon 13, the stereochemical configuration of all the metabolites involved in DIP synthesis was established by NMR analysis. The two inositol moieties in DIP had different stereochemical configurations, in contradiction of previous reports. The use of the designation di-myo-inositol-1,3'-phosphate is recommended to facilitate tracing individual carbon atoms through metabolic pathways.