The multifunctional role of ectoine as a natural cell protectant

Draft Genome Sequence of the Endophyte Paenibacillus sp. Strain GM2FR Isolated from Festuca rubra

Here, we report the 7.4-Mb draft genome sequence of Paenibacillus sp. strain GM2FR, an endophytic bacterium isolated from aerial plant tissues of Festuca rubra L. Genome analysis revealed 6,652 coding gene sequences and several gene clusters involved in plant growth promotion, such as that for the siderophore bacillibactin.

Production and characterization of ectoine using a moderately halophilic strain Halomonas salina BCRC17875

This study attempted to utilize Halomonas salina BCRC17875 to produce ectoine by optimizing the agitation speed and medium composition. In addition, the chemical structure of ectoine produced by H. salina BCRC17875 was determined. The results indicate that ectoine production reached 3.65 g/L at 38 h of cultivation when the agitation rate and NaCl concentration were fixed at 200 rpm and 2.0 M, respectively. It reached 9.20 g/L at 44 h of cultivation when the major medium components were yeast extract (56 g/L), glutamate (74.40 g/L), and ammonium sulfate (14 g/L). After the nitrogen concentration had been evaluated, evaluation of the nitrogen concentration revealed that the ectoine production reached 11.80 g/L at 44 h of cultivation when 56 g/L of yeast extract and 28 g/L of ammonium sulfate were used. Ectoine production reached 13.96 g/L at 44 h of cultivation when the carbon/nitrogen ratio was fixed at 3/1 using 84 g/L of yeast extract and 28 g/L of ammonium sulfate. Furthermore, the identification of ectoine were identified and characterized by fast atom bombardment mass spectrometry (FAB-MS) and ¹H NMR. The results demonstrated a fermentation strategy was successful in increasing ectoine production, and that the fermentation medium of ectoine had commercialization potential.

Tinkering with Osmotically Controlled Transcription Allows Enhanced Production and Excretion of Ectoine and Hydroxyectoine from a Microbial Cell Factory

Ectoine and hydroxyectoine are widely synthesized by members of the Bacteria and a few members of the Archaea as potent osmostress protectants. We have studied the salient features of the osmostress-responsive promoter directing the transcription of the ectoine/hydroxyectoine biosynthetic gene cluster from the plant-root-associated bacterium Pseudomonas stutzeri by transferring it into Escherichia coli, an enterobacterium that does not produce ectoines naturally. Using ect-lacZ reporter fusions, we found that the heterologous ect promoter reacted with exquisite sensitivity in its transcriptional profile to graded increases in sustained high salinity, responded to a true osmotic signal, and required the buildup of an osmotically effective gradient across the cytoplasmic membrane for its induction. The involvement of the -10, -35, and spacer regions of the sigma-70-type ect promoter in setting promoter strength and response to osmotic stress was assessed through site-directed mutagenesis. Moderate changes in the ect promoter sequence that increase its resemblance to housekeeping sigma-70-type promoters of E. coli afforded substantially enhanced expression, both in the absence and in the presence of osmotic stress. Building on this set of ect promoter mutants, we engineered an E. coli chassis strain for the heterologous production of ectoines. This synthetic cell factory lacks the genes for the osmostress-responsive synthesis of trehalose and the compatible solute importers ProP and ProU, and it continuously excretes ectoines into the growth medium. By combining appropriate host strains and different plasmid variants, excretion of ectoine, hydroxyectoine, or a mixture of both compounds was achieved under mild osmotic stress conditions.IMPORTANCE Ectoines are compatible solutes, organic osmolytes that are used by microorganisms to fend off the negative consequences of high environmental osmolarity on cellular physiology. An understanding of the salient features of osmostress-responsive promoters directing the expression of the ectoine/hydroxyectoine biosynthetic gene clusters is lacking. We exploited the ect promoter from an ectoine/hydroxyectoine-producing soil bacterium for such a study by transferring it into a surrogate bacterial host. Despite the fact that E. coli does not synthesize ectoines naturally, the ect promoter retained its exquisitely sensitive osmotic control, indicating that osmoregulation of ect transcription is an inherent feature of the promoter and its flanking sequences. These sequences were narrowed to a 116-bp DNA fragment. Ectoines have interesting commercial applications. Building on data from a site-directed mutagenesis study of the ect promoter, we designed a synthetic cell factory that secretes ectoine, hydroxyectoine, or a mixture of both compounds into the growth medium.

Hydration in aqueous solutions of ectoine and hydroxyectoine

We explore the influence of the two osmolytes ectoine and hydroxyectoine on the structure of pure water and aqueous NaCl solutions using non-resonant X-ray Raman scattering spectroscopy at the oxygen K-edge.

Poly(ectoine) Hydrogels Resist Nonspecific Protein Adsorption

The development of nonfouling zwitterionic materials has a wide range of biomedical and engineering applications. This work delineates the design and synthesis of a new zwitterionic material based on a naturally occurring compatible solute, ectoine, which is known to possess additional protective properties that stabilize even whole cells against ultraviolet radiation or cytotoxins. These properties and applications of ectoine inspire us to design a functional monomer containing the natural zwitterion moiety of ectoine imparting nonfouling properties and the methacrylate moiety for polymerization. The synthesis route designed for the ectoine methacrylate monomer is simple with a high yield, which is characterized by nuclear magnetic resonance spectroscopy and mass spectrometry. After monomer synthesis, we have prepared a poly(ectoine) hydrogel via thermal polymerization. The equilibrium water content, degree of cross-linking, mechanical strength, and nonfouling properties are determined for polyectoine hydrogels with different cross-linking conditions. Poly(ectoine) hydrogels are shown to have highly hydrated and excellent nonfouling properties and can be considered to be a promising biomaterial.

Design, Optimization and Application of Small Molecule Biosensor in Metabolic Engineering

The development of synthetic biology and metabolic engineering has painted a great future for the bio-based economy, including fuels, chemicals, and drugs produced from renewable feedstocks. With the rapid advance of genome-scale modeling, pathway assembling and genome engineering/editing, our ability to design and generate microbial cell factories with various phenotype becomes almost limitless. However, our lack of ability to measure and exert precise control over metabolite concentration related phenotypes becomes a bottleneck in metabolic engineering. Genetically encoded small molecule biosensors, which provide the means to couple metabolite concentration to measurable or actionable outputs, are highly promising solutions to the bottleneck. Here we review recent advances in the design, optimization and application of small molecule biosensor in metabolic engineering, with particular focus on optimization strategies for transcription factor (TF) based biosensors.

Applications for Marine Resources in Cosmetics

Marine resources represent an interesting source of active ingredients for the cosmetics industry. Algae (macro and micro) are rich in proteins, amino acids, carbohydrates, vitamins (A, B, and C) and oligo-elements such as copper, iron and zinc. All those active principles play roles in hydration, firming, slimming, shine and protection. Marine organisms inhabit a wide spectrum of habitats. Photo-protective compounds can be obtained from organisms subjected to strong light radiation, such as in tropical systems or in shallow water. In the same way, molecules with antioxidant potential can be obtained from microorganisms inhabiting extreme systems such as hydrothermal vents. For example, marine bacteria collected around deep-sea hydrothermal vents produce complex and innovative polysaccharides in the laboratory which are useful in cosmetics. There are many properties that will be put forward by the cosmetic industries.

Complete genome sequence of Microbulbifer sp. CCB-MM1, a halophile isolated from Matang Mangrove Forest, Malaysia

Microbulbifer sp. CCB-MM1 is a halophile isolated from estuarine sediment of Matang Mangrove Forest, Malaysia. Based on 16S rRNA gene sequence analysis, strain CCB-MM1 is a potentially new species of genus Microbulbifer. Here we describe its features and present its complete genome sequence with annotation. The genome sequence is 3.86 Mb in size with GC content of 58.85%, harbouring 3313 protein coding genes and 92 RNA genes. A total of 71 genes associated with carbohydrate active enzymes were found using dbCAN. Ectoine biosynthetic genes, ectABC operon and ask_ect were detected using antiSMASH 3.0. Cell shape determination genes, mreBCD operon, rodA and rodZ were annotated, congruent with the rod-coccus cell cycle of the strain CCB-MM1. In addition, putative mreBCD operon regulatory gene, bolA was detected, which might be associated with the regulation of rod-coccus cell cycle observed from the strain.

Bio-inspired solute enables preservation of human oocytes using minimum volume vitrification

The ability to cryopreserve human oocytes has significant potential for fertility preservation. Current cryopreservation methods still suffer from the use of conventional cryoprotectants, such as dimethyl sulphoxide (DMSO), causing loss of viability and function. Such injuries result from the toxicity and high concentration of cryoprotectants, as well as mechanical damage of cells due to ice crystal formation during the cooling and rewarming processes. Here we report the preservation of human oocytes following vitrification using an innovative bio-inspired cryoprotectant integrated with a minimum volume vitrification approach. The results demonstrate that the recovered human oocytes maintained viability following vitrification and rewarming. Moreover, when this approach was used to vitrify mouse oocytes, the recovered oocytes preserved their viability and function following vitrification and rewarming. This bio-inspired approach substitutes DMSO, a well-known toxic cryoprotectant, with ectoine, a non-toxic naturally occurring solute. The bio-inspired vitrification approach has the potential to improve fertility preservation for women undergoing cancer treatment and endangered mammal species.

Calling all hosts: Bacterial communication in situ

Bacteria are cosmopolitan organisms that in recent years have demonstrated many roles in maintaining host equilibrium. In this review, we discuss three roles bacteria can occupy in a host: pathogenic, symbiotic, and transient, with a specific focus on how bacterial small molecules contribute to homeostasis or dysbiosis. First, we will dissect how small molecules produced by pathogenic bacteria can be used as a source for communication during colonization and as protection against host immune responses. The ability to achieve a higher level of organization through small molecule communication gives pathogenic bacteria an opportunity for increased virulence and fitness. Conversely, in symbiotic relationships with hosts, small molecules are used in the initial acquisition, colonization, and maintenance of this beneficial population. Chemical signals can come from both the host and symbiont, and it is often observed that these interKingdom symbioses result in coevolution of both species involved. Furthermore, the transition from transient to commensal or opportunistic likely relies on molecular mechanisms. The small molecules utilized and produced by transient bacteria are desirable for both the immune and nutritional benefits they provide to the host. Finally, the advantages and disadvantages of modern analytical techniques that are available to researchers in order to study small molecules in situ is an important aspect of this review. It is our opinion that small molecules produced by bacteria are central to many biological processes and a larger focus on uncovering the function and identity of these small molecules is required to gain a deeper understanding of host-microbe associations.

-Genomic data mining of the marine actinobacteria Streptomyces sp. H-KF8 unveils insights into multi-stress related genes and metabolic pathways involved in antimicrobial synthesis

Streptomyces sp. H-KF8 is an actinobacterial strain isolated from marine sediments of a Chilean Patagonian fjord. Morphological characterization together with antibacterial activity was assessed in various culture media, revealing a carbon-source dependent activity mainly against Gram-positive bacteria (S. aureus and L. monocytogenes). Genome mining of this antibacterial-producing bacterium revealed the presence of 26 biosynthetic gene clusters (BGCs) for secondary metabolites, where among them, 81% have low similarities with known BGCs. In addition, a genomic search in Streptomyces sp. H-KF8 unveiled the presence of a wide variety of genetic determinants related to heavy metal resistance (49 genes), oxidative stress (69 genes) and antibiotic resistance (97 genes). This study revealed that the marine-derived Streptomyces sp. H-KF8 bacterium has the capability to tolerate a diverse set of heavy metals such as copper, cobalt, mercury, chromate and nickel; as well as the highly toxic tellurite, a feature first time described for Streptomyces. In addition, Streptomyces sp. H-KF8 possesses a major resistance towards oxidative stress, in comparison to the soil reference strain Streptomyces violaceoruber A3(2). Moreover, Streptomyces sp. H-KF8 showed resistance to 88% of the antibiotics tested, indicating overall, a strong response to several abiotic stressors. The combination of these biological traits confirms the metabolic versatility of Streptomyces sp. H-KF8, a genetically well-prepared microorganism with the ability to confront the dynamics of the fjord-unique marine environment.

Biotechnological Applications of Marine Enzymes From Algae, Bacteria, Fungi, and Sponges

Diversity is the hallmark of all life forms that inhabit the soil, air, water, and land. All these habitats pose their unique inherent challenges so as to breed the "fittest" creatures. Similarly, the biodiversity from the marine ecosystem has evolved unique properties due to challenging environment. These challenges include permafrost regions to hydrothermal vents, oceanic trenches to abyssal plains, fluctuating saline conditions, pH, temperature, light, atmospheric pressure, and the availability of nutrients. Oceans occupy 75% of the earth's surface and harbor most ancient and diverse forms of organisms (algae, bacteria, fungi, sponges, etc.), serving as an excellent source of natural bioactive molecules, novel therapeutic compounds, and enzymes. In this chapter, we introduce enzyme technology, its current state of the art, unique enzyme properties, and the biocatalytic potential of marine algal, bacterial, fungal, and sponge enzymes that have indeed boosted the Marine Biotechnology Industry. Researchers began exploring marine enzymes, and today they are preferred over the chemical catalysts for biotechnological applications and functions, encompassing various sectors, namely, domestic, industrial, commercial, and healthcare. Next, we summarize the plausible pros and cons: the challenges encountered in the process of discovery of the potent compounds and bioactive metabolites such as biocatalysts/enzymes of biomedical, therapeutic, biotechnological, and industrial significance. The field of Marine Enzyme Technology has recently assumed importance, and if it receives further boost, it could successfully substitute other chemical sources of enzymes useful for industrial and commercial purposes and may prove as a beneficial and ecofriendly option. With appropriate directions and encouragement, marine enzyme technology can sustain the rising demand for enzyme production while maintaining the ecological balance, provided any undesired exploitation of the marine ecosystem is avoided.

Neutrons describe ectoine effects on water H-bonding and hydration around a soluble protein and a cell membrane

Understanding adaptation to extreme environments remains a challenge of high biotechnological potential for fundamental molecular biology. The cytosol of many microorganisms, isolated from saline environments, reversibly accumulates molar concentrations of the osmolyte ectoine to counterbalance fluctuating external salt concentrations. Although they have been studied extensively by thermodynamic and spectroscopic methods, direct experimental structural data have, so far, been lacking on ectoine-water-protein interactions. In this paper, in vivo deuterium labeling, small angle neutron scattering, neutron membrane diffraction and inelastic scattering are combined with neutron liquids diffraction to characterize the extreme ectoine-containing solvent and its effects on purple membrane of H. salinarum and E. coli maltose binding protein. The data reveal that ectoine is excluded from the hydration layer at the membrane surface and does not affect membrane molecular dynamics, and prove a previous hypothesis that ectoine is excluded from a monolayer of dense hydration water around the soluble protein. Neutron liquids diffraction to atomic resolution shows how ectoine enhances the remarkable properties of H-bonds in water—properties that are essential for the proper organization, stabilization and dynamics of biological structures.

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.

EctD-mediated biotransformation of the chemical chaperone ectoine into hydroxyectoine and its mechanosensitive channel-independent excretion

Background

Ectoine and its derivative 5-hydroxyectoine are cytoprotectants widely synthesized by microorganisms as a defense against the detrimental effects of high osmolarity on cellular physiology and growth. Both ectoines possess the ability to preserve the functionality of proteins, macromolecular complexes, and even entire cells, attributes that led to their description as chemical chaperones. As a consequence, there is growing interest in using ectoines for biotechnological purposes, in skin care, and in medical applications. 5-Hydroxyectoine is synthesized from ectoine through a region- and stereo-specific hydroxylation reaction mediated by the EctD enzyme, a member of the non-heme-containing iron(II) and 2-oxoglutarate-dependent dioxygenases. This chemical modification endows the newly formed 5-hydroxyectoine with either superior or different stress- protecting and stabilizing properties. Microorganisms producing 5-hydroxyectoine typically contain a mixture of both ectoines. We aimed to establish a recombinant microbial cell factory where 5-hydroxyectoine is (i) produced in highly purified form, and (ii) secreted into the growth medium.

Results

We used an Escherichia coli strain (FF4169) defective in the synthesis of the osmostress protectant trehalose as the chassis for our recombinant cell factory. We expressed in this strain a plasmid-encoded ectD gene from Pseudomonas stutzeri A1501 under the control of the anhydrotetracycline-inducible tet promoter. We chose the ectoine hydroxylase from P. stutzeri A1501 for our cell factory after a careful comparison of the in vivo performance of seven different EctD proteins. In the final set-up of the cell factory, ectoine was provided to salt-stressed cultures of strain FF4169 (pMP41; ectD⁺). Ectoine was imported into the cells via the osmotically inducible ProP and ProU transport systems, intracellularly converted to 5-hydroxyectoine, which was then almost quantitatively secreted into the growth medium. Experiments with an E. coli mutant lacking all currently known mechanosensitive channels (MscL, MscS, MscK, MscM) revealed that the release of 5-hydroxyectoine under osmotic steady-state conditions occurred independently of these microbial safety valves. In shake-flask experiments, 2.13 g l⁻¹ ectoine (15 mM) was completely converted into 5-hydroxyectoine within 24 h.

Conclusions

We describe here a recombinant E. coli cell factory for the production and secretion of the chemical chaperone 5-hydroxyectoine free from contaminating ectoine.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-016-0525-4) contains supplementary material, which is available to authorized users.

Biochemistry and Crystal Structure of Ectoine Synthase: A Metal-Containing Member of the Cupin Superfamily

Ectoine is a compatible solute and chemical chaperone widely used by members of the Bacteria and a few Archaea to fend-off the detrimental effects of high external osmolarity on cellular physiology and growth. Ectoine synthase (EctC) catalyzes the last step in ectoine production and mediates the ring closure of the substrate N-gamma-acetyl-L-2,4-diaminobutyric acid through a water elimination reaction. However, the crystal structure of ectoine synthase is not known and a clear understanding of how its fold contributes to enzyme activity is thus lacking. Using the ectoine synthase from the cold-adapted marine bacterium Sphingopyxis alaskensis (Sa), we report here both a detailed biochemical characterization of the EctC enzyme and the high-resolution crystal structure of its apo-form. Structural analysis classified the (Sa)EctC protein as a member of the cupin superfamily. EctC forms a dimer with a head-to-tail arrangement, both in solution and in the crystal structure. The interface of the dimer assembly is shaped through backbone-contacts and weak hydrophobic interactions mediated by two beta-sheets within each monomer. We show for the first time that ectoine synthase harbors a catalytically important metal co-factor; metal depletion and reconstitution experiments suggest that EctC is probably an iron-dependent enzyme. We found that EctC not only effectively converts its natural substrate N-gamma-acetyl-L-2,4-diaminobutyric acid into ectoine through a cyclocondensation reaction, but that it can also use the isomer N-alpha-acetyl-L-2,4-diaminobutyric acid as its substrate, albeit with substantially reduced catalytic efficiency. Structure-guided site-directed mutagenesis experiments targeting amino acid residues that are evolutionarily highly conserved among the extended EctC protein family, including those forming the presumptive iron-binding site, were conducted to functionally analyze the properties of the resulting EctC variants. An assessment of enzyme activity and iron content of these mutants give important clues for understanding the architecture of the active site positioned within the core of the EctC cupin barrel.

Ectoine alleviates behavioural, physiological and biochemical changes in Daphnia magna subjected to formaldehyde

Ectoine (ECT) is produced by halophilic microorganisms in response to various stressful factors. Its protective properties in bacteria and some populations of isolated cells are known; however, no data are available on its protective influence on aquatic invertebrates subjected to a common pollutant, formaldehyde (FA). The purpose of this study was to determine the effects of FA alone (at 20 and 60 mg/L) and in the combination with various concentrations of ECT (5, 10 and 25 mg/L) at various times of exposure on behavioural, physiological and biochemical parameters of Daphnia magna. Specifically, mortality, heart rate, thoracic limb movement, reduced glutathione (GSH)/oxidised glutathione (GSSG) ratio, catalase (CAT) activity and nitric oxide (NOx) levels were determined. The results showed that both concentrations of FA when administered alone induced significant alterations of the determined parameters. On the other hand, animals treated with the combinations of FA + ECT showed decreased mortalities, attenuated inhibition of heart rates and thoracic limb activities, less decreased GSH/GSSG ratios, lower stimulation of CAT activities and NOx levels when compared to the crustaceans subjected to FA alone. The most distinct attenuation of toxic effects was observed in the combinations in which the highest concentrations of ECT were used. The results suggest that oxidative stress induced by FA in daphnids is likely to be alleviated by the antioxidative action of ECT.

Metabolomic Analysis of Blood Plasma after Oral Administration of N-acetyl-d-Glucosamine in Dogs

N-acetyl-d-glucosamine (GlcNAc) is a monosaccharide that polymerizes linearly through (1,4)-β-linkages. GlcNAc is the monomeric unit of the polymer chitin. GlcNAc is a basic component of hyaluronic acid and keratin sulfate found on the cell surface. The aim of this study was to examine amino acid metabolism after oral GlcNAc administration in dogs. Results showed that plasma levels of ectoine were significantly higher after oral administration of GlcNAc than prior to administration (p < 0.001). To our knowledge, there have been no reports of increased ectoine concentrations in the plasma. The mechanism by which GlcNAc administration leads to increased ectoine plasma concentration remains unclear; future studies are required to clarify this mechanism.

Overproduction, crystallization and X-ray diffraction data analysis of ectoine synthase from the cold-adapted marine bacterium Sphingopyxis alaskensis

Ectoine biosynthetic genes (ectABC) are widely distributed in bacteria. Microorganisms that carry them make copious amounts of ectoine as a cell protectant in response to high-osmolarity challenges. Ectoine synthase (EctC; EC 4.2.1.108) is the key enzyme for the production of this compatible solute and mediates the last step of ectoine biosynthesis. It catalyzes the ring closure of the cyclic ectoine molecule. A codon-optimized version of ectC from Sphingopyxis alaskensis (Sa) was used for overproduction of SaEctC protein carrying a Strep-tag II peptide at its carboxy-terminus. The recombinant SaEctC-Strep-tag II protein was purified to near-homogeneity from Escherichia coli cell extracts by affinity chromatography. Size-exclusion chromatography revealed that it is a dimer in solution. The SaEctC-Strep-tag II protein was crystallized using the sitting-drop vapour-diffusion method and crystals that diffracted to 1.0 Å resolution were obtained.

GlnR-Mediated Regulation of ectABCD Transcription Expands the Role of the GlnR Regulon to Osmotic Stress Management

Ectoine and hydroxyectoine are excellent compatible solutes for bacteria to deal with environmental osmotic stress and temperature damages. The biosynthesis cluster of ectoine and hydroxyectoine is widespread among microorganisms, and its expression is activated by high salinity and temperature changes. So far, little is known about the mechanism of the regulation of the transcription of ect genes and only two MarR family regulators (EctR1 in methylobacteria and the EctR1-related regulator CosR in Vibrio cholerae) have been found to negatively regulate the expression of ect genes. Here, we characterize GlnR, the global regulator for nitrogen metabolism in actinomycetes, as a negative regulator for the transcription of ectoine/hydroxyectoine biosynthetic genes (ect operon) in Streptomyces coelicolor. The physiological role of this transcriptional repression by GlnR is proposed to protect the intracellular glutamate pool, which acts as a key nitrogen donor for both the nitrogen metabolism and the ectoine/hydroxyectoine biosynthesis.

IMPORTANCE

High salinity is deleterious, and cells must evolve sophisticated mechanisms to cope with this osmotic stress. Although production of ectoine and hydroxyectoine is one of the most frequently adopted strategies, the in-depth mechanism of regulation of their biosynthesis is less understood. So far, only two MarR family negative regulators, EctR1 and CosR, have been identified in methylobacteria and Vibrio, respectively. Here, our work demonstrates that GlnR, the global regulator for nitrogen metabolism, is a negative transcriptional regulator for ect genes in Streptomyces coelicolor. Moreover, a close relationship is found between nitrogen metabolism and osmotic resistance, and GlnR-mediated regulation of ect transcription is proposed to protect the intracellular glutamate pool. Meanwhile, the work reveals the multiple roles of GlnR in bacterial physiology.

Design of an ectoine-responsive AraC mutant and its application in metabolic engineering of ectoine biosynthesis

Advanced high-throughput screening methods for small molecules may have important applications in the metabolic engineering of the biosynthetic pathways of these molecules. Ectoine is an excellent osmoprotectant that has been widely used in cosmetics. In this study, the Escherichia coli regulatory protein AraC was engineered to recognize ectoine as its non-natural effector and to activate transcription upon ectoine binding. As an endogenous reporter of ectoine, the mutated AraC protein was successfully incorporated into high-throughput screening of ectoine hyper-producing strains. The ectoine biosynthetic cluster from Halomonas elongata was cloned into E. coli. By engineering the rate-limiting enzyme L-2,4-diaminobutyric acid (DABA) aminotransferase (EctB), ectoine production and the specific activity of the EctB mutant were increased. Thus, these results demonstrated the effectiveness of engineering regulatory proteins into sensitive and rapid screening tools for small molecules and highlighted the importance and efficacy of directed evolution strategies applied to the engineering of genetic components for yield improvement in the biosynthesis of small molecules.

Protective effects of bacterial osmoprotectant ectoine on bovine erythrocytes subjected to staphylococcal alpha-haemolysin

Ectoine (ECT) is a bacterial compatible solute with documented protective action however no data are available on its effects on various cells against bacterial toxins. Therefore, we determined the in vitro influence of ECT on bovine erythrocytes subjected to staphylococcal α-haemolysin (HlyA). The cells exposed to HlyA alone showed a distinct haemolysis and reduced glutathione (GSH)/oxidised glutathione (GSSG) level, however the toxic effects were attenuated in the combinations of HlyA + ECT suggesting ECT-induced protection of erythrocytes from HlyA.

High production of ectoine from aspartate and glycerol by use of whole-cell biocatalysis in recombinant Escherichia coli

Background

Recently, the compatible solute 1, 4, 5, 6-tetrahydro-2-methyl-4-pyrimidinecarboxylic acid (ectoine) has attracted considerable interest due to its great potential as a protecting agent. To overcome the drawbacks of high salinity in the traditional bioprocess of ectoine using halophilic bacteria, various attempts have been made to engineer ectoine biosynthesis in nonhalophilic bacteria. Unfortunately, the yields of ectoine in these producers are still low and hardly meet the demands of large scale production. In this paper, the whole-cell biocatalytic process using aspartate and glycerol as substrates was tried for high production of ectoine in nonhalophilic bacteria.

Results

The ectoine genes ectABC from the halophilic bacterium Halomonas elongata were successfully introduced into Escherichia coli K-12 strain BW25113 under the arabinose-inducible promoter. To our delight, a large amount of ectoine was synthesized and excreted into the medium during the course of whole-cell biocatalysis, when using aspartate and glycerol as the direct substrates. At the low cell density of 5 OD/mL in flask, under the optimal conditions (100 mM sodium phosphate buffer (pH 7.0), 100 mM sodium aspartate, 100 mM KCl and 100 mM glycerol), the concentration of extracellular ectoine was increased to 2.67 mg/mL. At the high cell density of 20 OD/mL in fermentor, a maximum titre of 25.1 g/L ectoine was achieved in 24 h. Meanwhile, the biomass productivity of ectoine is as high as 4048 mg per gram dry cell weight (g DCW)⁻¹, which is the highest value ever reported. Furthermore, it was demonstrated that the same batch of cells could be used for at least three rounds. Finally, a total yield of 63.4 g ectoine was obtained using one litre cells.

Conclusion

Using aspartate and glycerol as the direct substrates, high production of ectoine was achieved by the whole-cell biocatalysis in recombinant E. coli. Multiple rounds of whole-cell biocatalysis were established to further improve the production of ectoine. Our study herein provided a feasible biosynthesis process of ectoine with potential applications in large-scale industrial production.

Characteristics of Meningitis Due to Methylobacterium mesophilicum: A Rare Case

Methylobacterium mesophilicum is a gram-negative bacillus most often isolated in medical establishments. In humans, M. mesophilicum is considered a conditionally pathogenic flora. Infections in humans generally occur in immunodeficient individuals. This article describes a rare case of M. mesophilicum infection that developed into acute meningitis in a 26-year-old patient. Decreased neutrophil bactericidal activity was also detected. To our knowledge, there have been no previous reports of meningitis due to M. mesophilicum.

Effects of ectoine on behavioural, physiological and biochemical parameters of Daphnia magna

Ectoine (ECT) is a compatible solute produced by soil, marine and freshwater bacteria in response to stressful factors. The purpose of our study was to determine the possible toxic influence of ECT on Daphnia magna. We determined the following endpoints: survival rate during exposure and recovery, swimming performance, heart rate, thoracic limb movement determined by image analysis, haemoglobin level by ELISA assay, catalase and nitric oxide species (NOx) by spectrophotometric methods. The results showed 80% survival of daphnids exposed to 50mg/L of ECT after 24h and 10% after 90h, however lower concentrations of ECT were well tolerated. A concentration-dependent reduction of swimming velocity was noted at 24 and 48h of the exposure. ECT (at 2.5 and 4mg/L) induced an increase of heart rate and thoracic limb movement (at 2.5, 4 and 20mg/L) after 24h. After 10h of the exposure to ECT daphnids showed a concentration-dependent increase of haemoglobin level synthesized and accumulated in the epipodite epithelia. After 24h we noted a concentration-dependent decrease of haemoglobin level and its lowest value was found after 48h of the exposure. ECT at a concentration of 20 and 25mg/L slightly stimulated catalase activity after 24h. NOx level was also increased after 10h of the exposure to 20 and 25mg/L of ECT reaching maximal activity after 24h. Our results suggest that ECT possesses some modulatory potential on the behaviour, physiology and biochemical parameters in daphnids.

Crystal structure of the ectoine hydroxylase, a snapshot of the active site

Ectoine and its derivative 5-hydroxyectoine are compatible solutes that are widely synthesized by bacteria to cope physiologically with osmotic stress. They also serve as chemical chaperones and maintain the functionality of macromolecules. 5-Hydroxyectoine is produced from ectoine through a stereo-specific hydroxylation, an enzymatic reaction catalyzed by the ectoine hydroxylase (EctD). The EctD protein is a member of the non-heme-containing iron(II) and 2-oxoglutarate-dependent dioxygenase superfamily and is evolutionarily well conserved. We studied the ectoine hydroxylase from the cold-adapted marine ultra-microbacterium Sphingopyxis alaskensis (Sa) and found that the purified SaEctD protein is a homodimer in solution. We determined the SaEctD crystal structure in its apo-form, complexed with the iron catalyst, and in a form that contained iron, the co-substrate 2-oxoglutarate, and the reaction product of EctD, 5-hydroxyectoine. The iron and 2-oxoglutarate ligands are bound within the EctD active site in a fashion similar to that found in other members of the dioxygenase superfamily. 5-Hydroxyectoine, however, is coordinated by EctD in manner different from that found in high affinity solute receptor proteins operating in conjunction with microbial import systems for ectoines. Our crystallographic analysis provides a detailed view into the active site of the ectoine hydroxylase and exposes an intricate network of interactions between the enzyme and its ligands that collectively ensure the hydroxylation of the ectoine substrate in a position- and stereo-specific manner.

Noninterventional open-label trial investigating the efficacy and safety of ectoine containing nasal spray in comparison with beclomethasone nasal spray in patients with allergic rhinitis

Objectives. The current study aimed to compare the efficacy and safety of a classical anti-inflammatory beclomethasone nasal spray in comparison to a physic-chemical stabilizing ectoine containing nasal spray in the treatment of allergic rhinitis. Design and Methods. This was a noninterventional, open-label, observational trial investigating the effects of beclomethasone or ectoine nasal spray on nasal symptoms and quality of life. Over a period of 14 days, patients were asked to daily document their symptoms. Efficacy and tolerability were assessed by both physicians and patients. Results. Both treatments resulted in a significant decrease of TNSS values. An equivalence test could not confirm the noninferiority of ectoine treatment in comparison with beclomethasone treatment. Although clear symptom reduction was achieved with the ectoine products, the efficacy judgment showed possible advantages for the beclomethasone group. Importantly, tolerability results were comparably good in both groups, and a very low number of adverse events supported this observation. Both treatments resulted in a clear improvement in the quality of life as assessed by a questionnaire answered at the beginning and at the end of the trial. Conclusion. Taken together, it was shown that allergic rhinitis can be safely and successfully treated with beclomethasone and also efficacy and safety were shown for ectoine nasal spray.

Treatment of rhinitis sicca anterior with ectoine containing nasal spray

Objectives. The safety and efficacy of ectoine nasal spray and ectoine nasal spray with dexpanthenol in the treatment of rhinitis sicca were evaluated in two studies. Design and Methods. Two noninterventional observational studies were performed to evaluate the efficacy and safety of a nasal spray containing ectoine (study 1) and ectoine/dexpanthenol (study 2) over a period of two weeks including comparable numbers of patients suffering from rhinitis sicca anterior. Patients and physicians were asked to rate the efficacy in reducing symptoms and the tolerability over the treatment phase. Results. The treatment in both studies resulted in a clinical and statistical significant reduction of the main diagnosis parameters, nasal airway obstruction, and crust formation. There was also a significant reduction in the secondary diagnosis parameters in both studies. Importantly, the tolerability was very good. During the whole observational study, neither patients nor doctors stopped the medication due to unwanted effects. Conclusion. Rhinitis sicca could be successfully treated with a nasal spray containing ectoine and a nasal spray combining ectoine with dexpanthenol. The combination of both substances led to slight advantages.

Biochemical properties of ectoine hydroxylases from extremophiles and their wider taxonomic distribution among microorganisms

Ectoine and hydroxyectoine are well-recognized members of the compatible solutes and are widely employed by microorganisms as osmostress protectants. The EctABC enzymes catalyze the synthesis of ectoine from the precursor L-aspartate-β-semialdehyde. A subgroup of the ectoine producers can convert ectoine into 5-hydroxyectoine through a region-selective and stereospecific hydroxylation reaction. This compatible solute possesses stress-protective and function-preserving properties different from those of ectoine. Hydroxylation of ectoine is carried out by the EctD protein, a member of the non-heme-containing iron (II) and 2-oxoglutarate-dependent dioxygenase superfamily. We used the signature enzymes for ectoine (EctC) and hydroxyectoine (EctD) synthesis in database searches to assess the taxonomic distribution of potential ectoine and hydroxyectoine producers. Among 6428 microbial genomes inspected, 440 species are predicted to produce ectoine and of these, 272 are predicted to synthesize hydroxyectoine as well. Ectoine and hydroxyectoine genes are found almost exclusively in Bacteria. The genome context of the ect genes was explored to identify proteins that are functionally associated with the synthesis of ectoines; the specialized aspartokinase Ask_Ect and the regulatory protein EctR. This comprehensive in silico analysis was coupled with the biochemical characterization of ectoine hydroxylases from microorganisms that can colonize habitats with extremes in salinity (Halomonas elongata), pH (Alkalilimnicola ehrlichii, Acidiphilium cryptum), or temperature (Sphingopyxis alaskensis, Paenibacillus lautus) or that produce hydroxyectoine very efficiently over ectoine (Pseudomonas stutzeri). These six ectoine hydroxylases all possess similar kinetic parameters for their substrates but exhibit different temperature stabilities and differ in their tolerance to salts. We also report the crystal structure of the Virgibacillus salexigens EctD protein in its apo-form, thereby revealing that the iron-free structure exists already in a pre-set configuration to incorporate the iron catalyst. Collectively, our work defines the taxonomic distribution and salient biochemical properties of the ectoine hydroxylase protein family and contributes to the understanding of its structure.

Glass-forming property of hydroxyectoine is the cause of its superior function as a desiccation protectant

We were able to demonstrate that hydroxyectoine, in contrast to ectoine, is a good glass-forming compound. Fourier transform infrared and spin label electron spin resonance studies of dry ectoine and hydroxyectoine have shown that the superior glass-forming properties of hydroxyectoine result from stronger intermolecular H-bonds with the OH group of hydroxyectoine. Spin probe experiments have also shown that better molecular immobilization in dry hydroxyectoine provides better redox stability of the molecules embedded in this dry matrix. With a glass transition temperature of 87°C (vs. 47°C for ectoine) hydroxyectoine displays remarkable desiccation protection properties, on a par with sucrose and trehalose. This explains its accumulation in response to increased salinity and elevated temperature by halophiles such as Halomonas elongata and its successful application in ``anhydrobiotic engineering'' of both enzymes and whole cells.

Overexpression, crystallization and preliminary X-ray crystallographic analysis of the ectoine hydroxylase from Sphingopyxis alaskensis

The ectoine hydroxylase (EctD) is a member of the non-haem-containing iron(II)- and 2-oxoglutarate-dependent dioxygenase superfamily. Its mononuclear iron centre is a prerequisite for the activity of this enzyme and promotes the O2-dependent oxidative decarboxylation of 2-oxoglutarate, which is coupled to a two-electron oxidation of the substrate ectoine to yield 5-hydroxyectoine. An expression and purification protocol for the EctD enzyme from Sphingopyxis alaskensis was developed and the protein was crystallized using the sitting-drop vapour-diffusion method. This resulted in two different crystal forms, representing the apo and iron-bound forms of the enzyme.

Diversity of the ectoines biosynthesis genes in the salt tolerant Streptomyces and evidence for inductive effect of ectoines on their accumulation

Streptomyces commonly produce ectoines as compatible solutes to prevent osmotic stresses. Fine structure of the genes producing ectoine (ectC) and hydroxyectoine (ectD) enzymes in Streptomyces rimosus C-2012 as a slightly halophilic bacterium is reported in this study. Deduced amino acid sequences of ectC and ectD genes from strain C-2012 and some other related species were compared and 72-90% and 13-81% identities were detected for ectC and ectD, respectively. High similarity of ectC between closely or distantly related Streptomyces to the strain C-2012 may indicate horizontal transfer of this gene. However, phylogenetic relationships of ectD were correlated with phylogenetic affiliation of the strains. It suggests that the ability of Streptomyces to produce hydroxyectoine has been the result of a vertical transfer event. HPLC analysis showed that strain C-2012 was able to produce ectoine and hydroxyectoine both in the presence and absence of external salinity (up to 0.45 M NaCl). Accordingly, reverse transcription quantitative PCR (RT-qPCR) showed that ectABCD operon in this strain is positively affected by salt. Also, inductive effect of the salt was increased when it was applied with 1 mM of ectoines. Transcription level of ectC was increased 2.7- and 2.9-fold in the medium supplied with salt and ectoine and salt and hydroxyectoine, respectively. The effect of salinity with or without ectoines was more on ectD transcription level than that of ectC. In S. rimosus under salt stress, ectoine and hydroxyectoine biosynthesis primarily depends on the stimulation of ectABCD operon transcription. However, drastic accumulation of ectoine and hydroxyectoine without increase in ectC and ectD transcripts was observed in the medium supplied with salt and ectoines and that suggest there might be additional posttranscriptional level of control. Increases in ratio of some intracellular free amino acids in salt stressed to unstressed conditions were observed in cells grown with ectoines. Our results suggest the possibility of a supplementary role of ectoines to improve structure and function of the cells in stressful environments as well as their important role as osmoprotectants.

Systems metabolic engineering of Corynebacterium glutamicum for production of the chemical chaperone ectoine

Background

The stabilizing and function-preserving effects of ectoines have attracted considerable biotechnological interest up to industrial scale processes for their production. These rely on the release of ectoines from high-salinity-cultivated microbial producer cells upon an osmotic down-shock in rather complex processor configurations. There is growing interest in uncoupling the production of ectoines from the typical conditions required for their synthesis, and instead design strains that naturally release ectoines into the medium without the need for osmotic changes, since the use of high-salinity media in the fermentation process imposes notable constraints on the costs, design, and durability of fermenter systems.

Results

Here, we used a Corynebacterium glutamicum strain as a cellular chassis to establish a microbial cell factory for the biotechnological production of ectoines. The implementation of a mutant aspartokinase enzyme ensured efficient supply of L-aspartate-beta-semialdehyde, the precursor for ectoine biosynthesis. We further engineered the genome of the basic C. glutamicum strain by integrating a codon-optimized synthetic ectABCD gene cluster under expressional control of the strong and constitutive C. glutamicum tuf promoter. The resulting recombinant strain produced ectoine and excreted it into the medium; however, lysine was still found as a by-product. Subsequent inactivation of the L-lysine exporter prevented the undesired excretion of lysine while ectoine was still exported. Using the streamlined cell factory, a fed-batch process was established that allowed the production of ectoine with an overall productivity of 6.7 g L^-1 day^-1 under growth conditions that did not rely on the use of high-salinity media.

Conclusions

The present study describes the construction of a stable microbial cell factory for recombinant production of ectoine. We successfully applied metabolic engineering strategies to optimize its synthetic production in the industrial workhorse C. glutamicum and thereby paved the way for further improvements in ectoine yield and biotechnological process optimization.

Molecular dynamics simulations and structure-guided mutagenesis provide insight into the architecture of the catalytic core of the ectoine hydroxylase

Many bacteria amass compatible solutes to fend-off the detrimental effects of high osmolarity on cellular physiology and water content. These solutes also function as stabilizers of macromolecules, a property for which they are referred to as chemical chaperones. The tetrahydropyrimidine ectoine is such a compatible solute and is widely synthesized by members of the Bacteria. Many ectoine producers also synthesize the stress protectant 5-hydroxyectoine from the precursor ectoine, a process that is catalyzed by the ectoine hydroxylase (EctD). The EctD enzyme is a member of the non-heme-containing iron(II) and 2-oxoglutarate-dependent dioxygenase superfamily. A crystal structure of the EctD protein from the moderate halophile Virgibacillus salexigens has previously been reported and revealed the coordination of the iron catalyst, but it lacked the substrate ectoine and the co-substrate 2-oxoglutarate. Here we used this crystal structure as a template to assess the likely positioning of the ectoine and 2-oxoglutarate ligands within the active site by structural comparison, molecular dynamics simulations, and site-directed mutagenesis. Collectively, these approaches suggest the positioning of the iron, ectoine, and 2-oxoglutarate ligands in close proximity to each other and with a spatial orientation that will allow the region-selective and stereo-specific hydroxylation of (4S)-ectoine to (4S,5S)-5-hydroxyectoine. Our study thus provides a view into the catalytic core of the ectoine hydroxylase and suggests an intricate network of interactions between the three ligands and evolutionarily highly conserved residues in members of the EctD protein family.

Ectoine-containing cream in the treatment of mild to moderate atopic dermatitis: a randomised, comparator-controlled, intra-individual double-blind, multi-center trial

INTRODUCTION

The natural cyclic tetrahydropyrimidine, ectoine, is a low-molecular, water-binding, organic osmolyte. Previously, topical application of ectoine to healthy human skin was shown to improve skin hydration as well as skin barrier function.

OBJECTIVES

We therefore speculated that topical application of ectoine would be beneficial for patients with atopic dermatitis (AD), in which a genetically defined defect in skin barrier function is of major pathogenetic relevance. We assessed the efficacy of an ectoine-containing cream (EHK02-01) in the management of 65 patients with mild to moderate AD in a randomized, intra-individual, double-blind, multi-center trial, in which the efficacy of ectoine was compared to a nonsteroidal anti-inflammatory cream previously found to primarily act on skin barrier function and therefore with a comparable mode of action.

METHODS

Sixty-five patients with mild to moderate AD aged 18-65 years were enrolled. The patients applied EHK02-01 and the control cream on two symmetrical lesions twice daily for 28 days. At the beginning, after 7 and after 28 days, treated skin areas were assessed by modified, objective local SCORAD (Scoring Atopic Dermatitis) and IGA (Investigator's Global Assessment) as well as the patients' judgment of efficacy and their assessment of pruritus.

RESULTS

EHK02-01 was found to be very well tolerated. Even more important, efficacy of EHK02-01 treatment was equivalent to that achieved with the reference product.

CONCLUSION

These results indicate that topical treatment with EHK02-01 may represent a novel option for the treatment of patients with AD.

A prospective, controlled study of SNS01 (ectoine nasal spray) compared to BNO-101 (phytotherapeutic dragées) in patients with acute rhinosinusitis

OBJECTIVES

In this observational study, data on the efficacy, effects on quality of life and tolerability of the topical formulation SNS01 (Ectoin Rhinitis nasal spray) were compared to those of BNO-101 (Sinupret forte dragées) in patients with acute rhinosinusitis in the ear, nose, and throat (ENT) clinical setting.

DESIGN AND METHODS

Patients with the diagnosis of acute rhinosinusitis were included in this non-interventional study with a treatment duration of 14-16 days. They received either a herbal phytotherapeutic dragée (control) or an ectoine-based nasal spray (investigational product), each to be taken according to the instructions for use (IFU) and summary of product characteristics (SPC). At each visit, the physician performed a nasal endoscopy, recorded the Sinusitis Symptom Score and checked for adverse events. During the entire treatment period, patients recorded the Sinusitis Symptom Score in patient diaries. In addition, patients receiving the nasal spray filled out a questionnaire to assess the tolerability of the treatment. To investigate effects on quality of life patients were asked to fill out the German version of a sinusitis-specific HRQL (health related quality of life) questionnaire.

CLINICAL TRIAL REGISTRATION

NCT01684540.

RESULTS

Patient diary entries, the assessment of the Sinusitis Symptom Score and the HRQL questionnaire demonstrated that the ectoine nasal spray was as effective as the phytotherapeutic dragées in treating acute rhinosinusitis. After two weeks of treatment, the assessments of both the patients' diaries and physicians' record forms indicated statistically significant improvement (p ≤ 0.001) in the symptom scores of the two groups (57.8% improvement for ectoine and 49.3% improvement for the phytotherapeutic dragées compared to baseline). Also, overall scores of 80 in the sensory questionnaire confirmed the good tolerability of the nasal spray. Correspondingly, HRQL improved significantly over the course of the treatment in both groups.

CONCLUSION

SNS01 and BNO-101 demonstrated comparable effects in the treatment of acute rhinosinusitis.

LIMITATIONS

Following German regulations, this trial was set up as an observational 'non-interventional' study, which does not allow for a placebo group or randomization of patients. Although the grade of evidence delivered by the study data is thus reduced from Ib to IIa, it does, however, reflect a realistic view of the most common clinical practice.