Impact of the neurotoxin β-N-methylamino-L-alanine on the diatom Thalassiosira pseudonana using metabolomics

The neurotoxin β-N-methylamino-L-alanine (BMAA) has emerged as an environmental factor related to neurodegenerative diseases. BMAA is produced by various microorganisms including cyanobacteria and diatoms, in diverse ecosystems. In the diatom Phaeodactylum tricornutum, BMAA is known to inhibit growth. The present study investigated the impact of BMAA on the diatom Thalassiosira pseudonana by exposing it to different concentrations of exogenous BMAA. Metabolomics was predominantly employed to investigate the effect of BMAA on T. pseudonana, and MetaboAnalyst (https://www.metabo-analyst.ca/) was used to identify BMAA-associated metabolisms/pathways in T. pseudonana. Furthermore, to explore the unique response, specific metabolites were compared between treatments. When the growth was obstructed by BMAA, 17 metabolisms/pathways including nitrogen and glutathione (i.e. oxidative stress) metabolisms, were influenced in T. pseudonana. This study has further determined that 11 out of 17 metabolisms/pathways could be essentially affected by BMAA, leading to the inhibition of diatom growth.

Temporal dynamics of stress response in Halomonas elongata to NaCl shock: physiological, metabolomic, and transcriptomic insights

BACKGROUND

The halophilic bacterium Halomonas elongata is an industrially important strain for ectoine production, with high value and intense research focus. While existing studies primarily delve into the adaptive mechanisms of this bacterium under fixed salt concentrations, there is a notable dearth of attention regarding its response to fluctuating saline environments. Consequently, the stress response of H. elongata to salt shock remains inadequately understood.

RESULTS

This study investigated the stress response mechanism of H. elongata when exposed to NaCl shock at short- and long-time scales. Results showed that NaCl shock induced two major stresses, namely osmotic stress and oxidative stress. In response to the former, within the cell's tolerable range (1-8% NaCl shock), H. elongata urgently balanced the surging osmotic pressure by uptaking sodium and potassium ions and augmenting intracellular amino acid pools, particularly glutamate and glutamine. However, ectoine content started to increase until 20 min post-shock, rapidly becoming the dominant osmoprotectant, and reaching the maximum productivity (1450 ± 99 mg/L/h). Transcriptomic data also confirmed the delayed response in ectoine biosynthesis, and we speculate that this might be attributed to an intracellular energy crisis caused by NaCl shock. In response to oxidative stress, transcription factor cysB was significantly upregulated, positively regulating the sulfur metabolism and cysteine biosynthesis. Furthermore, the upregulation of the crucial peroxidase gene (HELO_RS18165) and the simultaneous enhancement of peroxidase (POD) and catalase (CAT) activities collectively constitute the antioxidant defense in H. elongata following shock. When exceeding the tolerance threshold of H. elongata (1-13% NaCl shock), the sustained compromised energy status, resulting from the pronounced inhibition of the respiratory chain and ATP synthase, may be a crucial factor leading to the stagnation of both cell growth and ectoine biosynthesis.

CONCLUSIONS

This study conducted a comprehensive analysis of H. elongata's stress response to NaCl shock at multiple scales. It extends the understanding of stress response of halophilic bacteria to NaCl shock and provides promising theoretical insights to guide future improvements in optimizing industrial ectoine production.

Protective effects of ectoine on articular chondrocytes and cartilage in rats for treating osteoarthritis

Osteoarthritis (OA) is a chronic degenerative disease that primarily includes articular cartilage destruction and inflammatory reactions, and effective treatments for this disease are still lacking. The present study aimed to explore the protective effects of ectoine, a compatible solute found in nature, on chondrocytes in rats and its possible application in OA treatment. In the in vitro studies, the morphology of the chondrocytes after trypsin digestion for 2 min and the viability of the chondrocytes at 50°C were observed after ectoine treatment. The reactive oxygen species (ROS) levels in chondrocytes pretreated with ectoine and post-stimulated with H2O2 were detected using an ROS assay. Chondrocytes were pretreated with ectoine before IL-1β stimulation. RT‒qPCR was used to measure the mRNA levels of cyclooxygenase-2 (COX-2), metallomatrix proteinase-3, -9 (MMP-3, -9), and collagen type II alpha 1 (Col2A1). In addition, immunofluorescence was used to assess the expression of type II collagen. The in vivo effect of ectoine was evaluated in a rat OA model induced by the modified Hulth method. The findings revealed that ectoine significantly increased the trypsin tolerance of chondrocytes, maintained the viability of the chondrocytes at 50°C, and improved their resistance to oxidation. Compared with IL-1β treatment alone, ectoine pretreatment significantly reduced COX-2, MMP-3, and MMP-9 expression and maintained type II collagen synthesis in chondrocytes. In vivo, the cartilage of ectoine-treated rats exhibited less degeneration and lower Osteoarthritis Research Society International (OARSI) scores. The results of this study suggest that ectoine exerts protective effects on chondrocytes and cartilage and can, therefore, be used as a potential therapeutic agent in the treatment of OA.

The synthesis of ectoine enhance the assimilation of ammonia nitrogen in hypersaline wastewater by the salt-tolerant assimilation bacteria sludge

In contrast to nitrification-denitrification microorganisms that convert ammonia nitrogen in hypersaline wastewater into nitrogen for discharge, this research utilizes sludge enriched with salt-tolerant assimilation bacteria (STAB) to assimilate organic matter and ammonia nitrogen in hypersaline wastewater into ectoine - a biomass with high economic value and resistance to external osmotic pressure. The study investigates the relationship between the synthesis of ectoine and nitrogen removal efficiency of STAB sludge in three sequencing batch reactors (SBR) operated at different salinities (50, 75, and 100 g/L) and organic matter concentrations. The research reveals that, under low concentration carbon sources (TOC/N = 4, NH4+-N = 60 mg/L), the ammonia nitrogen removal efficiency of SBR reactors increased by 14.51 % and 17.25 % within 5 d and 2 d, respectively, when salinity increased from 50 g/L to 75 g/L and 100 g/L. Under high concentration carbon sources (TOC/N = 8, NH4+-N = 60 mg/L), the ammonia nitrogen removal efficiency of STAB sludge in the three reactors stabilized at 80.20 %, 76.71 %, and 72.87 %, and the total nitrogen removal efficiency was finally stabilized at 80.47 %, 73.15 %, and 65.53 %, respectively. The nitrogen removal performance by ammonium-assimilating of STAB sludge is more sustainable under low salinity, while it is more short-term explosive under high salinity. Moreover, the intracellular ectoine concentration of STAB sludge was found to be related to this behavior. Empirical formulas confirm that STAB sludge synthesizes ectoine from nutrients in wastewater through assimilation, and intracellular ectoine has a threshold defect (150 mg/gVss). The ectoine metabolism pathways of STAB sludge was constructed using the Kyoto Encyclopedia of Genes and Genomes (KEGG). The ammonia nitrogen in sewage is converted into glutamic acid under the action of assimilation genes. It then undergoes a tricarboxylic acid cycle to synthesize the crucial precursor of ectoine - aspartic acid. Subsequently, ectoine is produced through ectoine synthase. The findings suggest that when the synthesis of intracellular ectoine reaches saturation, it inhibits the continuous nitrogen removal performance of STAB sludge under high salinity. STAB sludge does not actively release ectoine through channels under stable external osmotic pressure.

Usage of ectoine as a cryoprotectant for cryopreservation of lactic acid bacteria

Streptococcus thermophilus, the only Streptococcus species considered "Generally Recognized Safe", has been used widely in the food industry. This bacterium is one of the most valuable industrial lactic acid bacterial species. Due to the importance of this bacterium in industrial applications, it should be stored for a long time without losing its metabolic properties. The present study aimed to investigate the cryoprotectant effect of three compatible solutes (ectoine, trehalose, and sucrose) on bacterial cells stored at different temperatures (frozen at -80 °C or freeze-dried and subsequently stored at +4, -20, and -80 °C) for three months. The bacterial cells were tested for cell viability, bile salt tolerance, and lactic acid production before and after processing. The highest cell viability, bile salt tolerance, and lactic acid production were obtained with ectoine and under frozen (storage at -80 °C) conditions. In freeze-dried and subsequently stored at various temperatures, the best preservation was obtained at -80 °C, followed by -20 °C and +4 °C. Moreover, when ectoine's preservation potential was compared to other cryoprotectants, ectoine showed the highest preservation, followed by trehalose and sucrose. Although ectoine has a variety of qualities that have been proven, in the current work, we have shown for the first time that ectoine has cryoprotectant potential in yogurt starter cultures (S. thermophilus).

2-Homoectoine: An Additional Member of the Ectoine Family from Phyto- and Bacterioplankton Involved in Osmoadaptation

Ectoine is a central osmolyte in marine plankton due to its excellent cytoprotective traits and its multifunctional roles supporting the survival of microalgae and bacteria under unfavorable environmental conditions. The protective effect of ectoine toward several kinds of stresses stirred interest in biotechnology, pharmacy, and other fields including cosmetics. Also, its hydroxylated derivative, 5-hydroxyectoine, exhibits functions similar to ectoine. Here we introduce a molecular networking-based approach to expand the family of ectoine derivatives from phyto- and bacterioplankton. A ZIC-HILIC separation protocol coupled with HRMS/MS-based molecular networking allowed us to identify the new ectoine derivative 1,4,5,6-tetrahydro-2-ethyl-4-pyrimidinecarboxylic acid, or 2-homoectoine (1). 1 is found in many algae including dinoflagellates, chlorophytes, and haptophytes. In axenic strains, the content of 1 is substantially lower. In accordance, we found that marine bacteria are prolific producers of the compound as well. This suggests that the microalgae with their associated microbiome have to be considered as sources of the compound. Increasing concentrations of the compound under high salinity suggest a role as a protectant against osmotic stress.

Metabolic engineering of high-salinity-induced biosynthesis of γ-aminobutyric acid improves salt-stress tolerance in a glutamic acid-overproducing mutant of an ectoine-deficient Halomonas elongata

A moderately halophilic eubacterium, Halomonas elongata, has been used as cell factory to produce fine chemical 1,4,5,6-tetrahydro-2-methyl-4-pyrimidinecarboxylic acid (ectoine), which functions as a major osmolyte protecting the cells from high-salinity stress. To explore the possibility of using H. elongata to biosynthesize other valuable osmolytes, an ectoine-deficient salt-sensitive H. elongata deletion mutant strain KA1 (ΔectABC), which only grows well in minimal medium containing up to 3% NaCl, was subjected to an adaptive mutagenesis screening in search of mutants with restored salt tolerance. Consequently, we obtained a mutant, which tolerates 6% NaCl in minimal medium by overproducing L-glutamic acid (Glu). However, this Glu-overproducing (GOP) strain has a lower tolerance level than the wild-type H. elongata, possibly because the acidity of Glu interferes with the pH homeostasis of the cell and hinders its own cellular accumulation. Enzymatic decarboxylation of Glu to γ-aminobutyric acid (GABA) by a Glu decarboxylase (GAD) could restore cellular pH homeostasis; therefore, we introduced an engineered salt-inducible HopgadBmut gene, which encodes a wide pH-range GAD mutant, into the genome of the H. elongata GOP strain. We found that the resulting H. elongata GOP-Gad strain exhibits higher salt tolerance than the GOP strain by accumulating high concentration of GABA as an osmolyte in the cell (176.94 µmol/g cell dry weight in minimal medium containing 7% NaCl). With H. elongata OUT30018 genetic background, H. elongata GOP-Gad strain can utilize biomass-derived carbon and nitrogen compounds as its sole carbon and nitrogen sources, making it a good candidate for the development of GABA-producing cell factories.IMPORTANCEWhile the wild-type moderately halophilic H. elongata can synthesize ectoine as a high-value osmolyte via the aspartic acid metabolic pathway, a mutant H. elongata GOP strain identified in this work opens doors for the biosynthesis of alternative valuable osmolytes via glutamic acid metabolic pathway. Further metabolic engineering to install a GAD system into the H. elongata GOP strain successfully created a H. elongata GOP-Gad strain, which acquired higher tolerance to salt stress by accumulating GABA as a major osmolyte. With the ability to assimilate biomass-derived carbon and nitrogen sources and thrive in high-salinity environment, the H. elongata GOP-Gad strain can be used in the development of sustainable GABA-producing cell factories.

Ectoines production from biogas in pilot bubble column bioreactors and their subsequent extraction via bio-milking

Despite the potential of biogas from waste/wastewater treatment as a renewable energy source, the presence of pollutants and the rapid decrease in the levelized cost of solar and wind power constrain the use of biogas for energy generation. Biogas conversion into ectoine, one of the most valuable bioproducts (1000 €/kg), constitutes a new strategy to promote a competitive biogas market. The potential for a stand-alone 20 L bubble column bioreactor operating at 6% NaCl and two 10 L interconnected bioreactors (at 0 and 6% NaCl, respectively) for ectoine production from biogas was comparatively assessed. The stand-alone reactor supported the best process performance due to its highest robustness and efficiency for ectoine accumulation (20-52 mgectoine/gVSS) and CH4 degradation (up to 84%). The increase in N availability and internal gas recirculation did not enhance ectoine synthesis. However, a 2-fold increase in the internal gas recirculation resulted in an approximately 1.3-fold increase in CH4 removal efficiency. Finally, the recovery of ectoine through bacterial bio-milking resulted in efficiencies of >70% without any negative impact of methanotrophic cell recycling to the bioreactors on CH4 biodegradation or ectoine synthesis.

NhaR, LeuO, and H-NS Are Part of an Expanded Regulatory Network for Ectoine Biosynthesis Expression

Bacteria accumulate compatible solutes to maintain cellular turgor pressure when exposed to high salinity. In the marine halophile Vibrio parahaemolyticus, the compatible solute ectoine is biosynthesized de novo, which is energetically more costly than uptake; therefore, tight regulation is required. To uncover novel regulators of the ectoine biosynthesis ectABC-asp_ect operon, a DNA affinity pulldown of proteins interacting with the ectABC-asp_ect regulatory region was performed. Mass spectrometry analysis identified, among others, 3 regulators: LeuO, NhaR, and the nucleoid associated protein H-NS. In-frame non-polar deletions were made for each gene and PectA-gfp promoter reporter assays were performed in exponential and stationary phase cells. PectA-gfp expression was significantly repressed in the ΔleuO mutant and significantly induced in the ΔnhaR mutant compared to wild type, suggesting positive and negative regulation, respectively. In the Δhns mutant, PectA-gfp showed increased expression in exponential phase cells, but no change compared to wild type in stationary phase cells. To examine whether H-NS interacts with LeuO or NhaR at the ectoine regulatory region, double deletion mutants were created. In a ΔleuO/Δhns mutant, PectA-gfp showed reduced expression, but significantly more than ΔleuO, suggesting H-NS and LeuO interact to regulate ectoine expression. However, ΔnhaR/Δhns had no additional effect compared to ΔnhaR, suggesting NhaR regulation is independent of H-NS. To examine leuO regulation further, a PleuO-gfp reporter analysis was examined that showed significantly increased expression in the ΔleuO, Δhns, and ΔleuO/Δhns mutants compared to wild type, indicating both are repressors. Growth pattern analysis of the mutants in M9G 6%NaCl showed growth defects compared to wild type, indicating that these regulators play an important physiological role in salinity stress tolerance outside of regulating ectoine biosynthesis gene expression. IMPORTANCE Ectoine is a commercially used compatible solute that acts as a biomolecule stabilizer because of its additional role as a chemical chaperone. A better understanding of how the ectoine biosynthetic pathway is regulated in natural bacterial producers can be used to increase efficient industrial production. The de novo biosynthesis of ectoine is essential for bacteria to survive osmotic stress when exogenous compatible solutes are absent. This study identified LeuO as a positive regulator and NhaR as a negative regulator of ectoine biosynthesis and showed that, similar to enteric species, LeuO is an anti-silencer of H-NS. In addition, defects in growth in high salinity among all the mutants suggest that these regulators play a broader role in the osmotic stress response beyond ectoine biosynthesis regulation.

Degradation of β-N-methylamino-l-alanine (BMAA) by UV/peracetic acid system: Influencing factors, degradation mechanism and DBP formation

β-N-methylamino-l-alanine (BMAA) is a cyanobacterial neurotoxin associated with human neurodegenerative diseases, and its removal in drinking water is receiving increasing attention. In this study, the degradation of BMAA in UV/peracetic acid (UV/PAA) system was investigated. BMAA degradation followed the pseudo-first-order kinetic model. The synergistic effect of UV and PAA exhibited a great potential for BMAA degradation, which was attributed to the generation of a large number of reactive radicals, of which R-C^• was the most dominant contributor. We also explored the effects of different factors on BMAA degradation. The results showed that there was a positive correlation between BMAA degradation and PAA dosage, and the optimal effect was achieved at pH 7. Notably, the existence of water matrices such as bicarbonate (HCO₃－), chloride ion (Cl－), humic acid (HA) and algal intracellular organic matter (IOM) all inhibited the degradation of BMAA. Based on the identified intermediates, this study suggested that reactive radicals degraded BMAA mainly by attacking the carbon-nitrogen bonds on BMAA. Besides, comparing the effect of Cl－ on disinfection byproduct (DBP) formation in UV/PAA-post-PAA oxidation and UV/chlorine-post-chlorination systems, it was found that the former was more sensitive to the presence of Cl－.

Biosynthesis of plant hemostatic dencichine in Escherichia coli

Dencichine is a plant-derived nature product that has found various pharmacological applications. Currently, its natural biosynthetic pathway is still elusive, posing challenge to its heterologous biosynthesis. In this work, we design artificial pathways through retro-biosynthesis approaches and achieve de novo production of dencichine. First, biosynthesis of the two direct precursors L-2, 3-diaminopropionate and oxalyl-CoA is achieved by screening and integrating microbial enzymes. Second, the solubility of dencichine synthase, which is the last and only plant-derived pathway enzyme, is significantly improved by introducing 28 synonymous rare codons into the codon-optimized gene to slow down its translation rate. Last, the metabolic network is systematically engineered to direct the carbon flux to dencichine production, and the final titer reaches 1.29 g L-1 with a yield of 0.28 g g-1 glycerol. This work lays the foundation for sustainable production of dencichine and represents an example of how synthetic biology can be harnessed to generate unnatural pathways to produce a desired molecule.

Exploring the Therapeutic Potential of Ectoine in Duchenne Muscular Dystrophy: Comparison with Taurine, a Supplement with Known Beneficial Effects in the mdx Mouse

Duchenne Muscular Dystrophy (DMD) is a debilitating muscle disorder that condemns patients to year-long dependency on glucocorticoids. Chronic glucocorticoid use elicits many unfavourable side-effects without offering satisfying clinical improvement, thus, the search for alternative treatments to alleviate muscle inflammation persists. Taurine, an osmolyte with anti-inflammatory effects, mitigated pathological features in the mdx mouse model for DMD but interfered with murine development. In this study, ectoine is evaluated as an alternative for taurine in vitro in CCL-136 cells and in vivo in the mdx mouse. Pre-treating CCL-136 cells with 0.1 mM taurine and 0.1 mM ectoine prior to exposure with 300 U/mL IFN-γ and 20 ng/mL IL-1β partially attenuated cell death, whilst 100 mM taurine reduced MHC-I protein levels. In vivo, histopathological features of the tibialis anterior in mdx mice were mitigated by ectoine, but not by taurine. Osmolyte treatment significantly reduced mRNA levels of inflammatory disease biomarkers, respectively, CCL2 and SPP1 in ectoine-treated mdx mice, and CCL2, HSPA1A, TNF-α and IL-1β in taurine-treated mdx mice. Functional performance was not improved by osmolyte treatment. Furthermore, ectoine-treated mdx mice exhibited reduced body weight. Our results confirmed beneficial effects of taurine in mdx mice and, for the first time, demonstrated similar and differential effects of ectoine.

Neurotoxin (N-Oxalyl-L-α,β-Diamino Propionic Acid) Content in Different Plant Parts of Grass Pea (Lathyrus sativus L.) Spanning Seedling to Maturity Stage: Does It Increase over Time?

ODAP (N-oxalyl-L-2,3-diaminopropionic acid) is present in the seeds of grass pea. In this study, variation of total ODAP accumulation in leaves throughout the crop growth starting from 40 days after sowing to maturity, and the distribution pattern of ODAP in different plant parts including the seeds at the mature stage was analyzed. Five grass pea accessions were evaluated for two subsequent growing seasons in one location of ICARDA, Aleppo (Syria). The results found that the rate of accumulation of total ODAP varied during plant development. Increased rates of synthesis were noticed in young leaves of grass pea. The highest total ODAP content in leaves was noted in the early growth stage (40-50 days after sowing). Mean total ODAP content in leaves ranged from 0.17 to 0.96 percent during 2010-2011 and from 0.19 to 1.28 percent during 2011-2012. During maturity, the total ODAP content was lowest in the seeds than in leaves, stems, pod cover, seed coat, and cotyledons. The ranges of total ODAP content were 0.13 (seed)-0.34 (stem), 0.20 (seed)-1.01 (leaf), 0.22 (seed)-0.62 (leaf), 0.21 (seed)-0.66 (leaf), and 0.21 (seed)-0.78 (leaf) percent in B387, B222, B390, Bio-520, and B587 accessions, respectively, during maturity. The results indicated that the rate of accumulation and synthesis of total ODAP varied during the plant lifespan. The lowest total ODAP content of leaves was observed after 130 days of sowing. The lower total ODAP content after the early vegetative stage of grass pea plants makes them suitable as a feed.

Role of abscisic acid in modulating drought acclimation, agronomic characteristics and β-N-oxalyl-L-α,β-diaminopropionic acid (β-ODAP) accumulation in grass pea (Lathyrus sativus L.)

BACKGROUND

β-N-oxalyl-l-α,β-diaminopropionic acid (β-ODAP) is a physiological indicator in response to drying soil. However, how abscisic acid (ABA) modulates β-ODAP accumulation and its related agronomic characteristics in drought stressed grass pea (Lathyrus sativus L.) continue to be unclear. The present study aimed to evaluate the effects of ABA addition on drought tolerance, agronomic characteristics and β-ODAP content in grass pea under drought stress.

RESULTS

Exogenous ABA significantly promoted ABA levels by 19.3% and 18.3% under moderate and severe drought stress, respectively, compared to CK (without ABA, used as control check treatment). ABA addition activated earlier trigger of non-hydraulic root-sourced signal at 69.1% field capacity (FC) (65.5% FC in CK) and accordingly prolonged its operation period to 45.6% FC (49.0% FC in CK). This phenomenon was mechanically associated with the physiological mediation of ABA, where its addition significantly promoted the activities of leaf superoxide dismutase, catalase and peroxidase enzymes and the biosynthesis of leaf proline, simultaneously lowering the accumulation of malondialdehyde and hydrogen peroxide under moderate and severe stresses. Interestingly, ABA application significantly increased seed β-ODAP content by 21.7% and 21.3% under moderate and severe drought stress, but did not change leaf β-ODAP content. Furthermore, ABA application produced similar shoot biomass and grain yield as control groups.

CONCLUSION

Exogenous ABA improved the drought adaptability of grass pea and promoted the synthesis of β-ODAP in seeds but not in leaves. Our findings provide novel insights into the agronomic role of ABA in relation to β-ODAP enrichment in grass pea subjected to drought stress. © 2021 Society of Chemical Industry.

Elimination of β-N-methylamino-l-alanine (BMAA) during UV/chlorine process: Influence factors, transformation pathway and DBP formation

As a new cyanobacterial neurotoxin generated by cyanobacteria, BMAA was closely related to amyotrophic lateral sclerosis-parkinsonism dementia complex (ALS/PDC). In this study, the degradation of BMAA by UV/chlorine process was investigated under the impacts of chlorine dosage, NOM dosage, pH and alkalinity. Results showed that only 10% of BMAA was removed by UV irradiation and 46.8% by chlorination in 5 min, however, 98.6% of BMAA was removed by UV/chlorine process in 5 min. The reaction rates were increased under alkaline conditions, but all achieved complete degradation in 5 min. Besides, HCO₃^- had slight inhibition, while NOM had significant inhibition on the degradation of BMAA. Furthermore, based on the detected degradation products of BMAA during UV/chlorine process, the possible degradation pathways were concluded. Overall, outcomes of this study exhibited that the use of the UV/chlorine process for BMAA degradation was appropriate in practical applications.

Elucidating the key environmental parameters during the production of ectoines from biogas by mixed methanotrophic consortia

Anaerobic digestion (AD) is a robust biotechnology for the valorisation of organic waste into biogas. However, the rapid decrease in renewable electricity prices requires alternative uses of biogas. In this context, the engineering of innovative platforms for the bio-production of chemicals from CH₄ has recently emerged. The extremolyte and osmoprotectant ectoine, with a market price of ~1000€/Kg, is the industrial flagship of CH₄-based bio-chemicals. This work aimed at optimizing the accumulation of ectoines using mixed microbial consortia enriched from saline environments (a salt lagoon and a salt river) and activated sludge, and biogas as feedstock. The influence of NaCl (0, 3, 6, 9 and 12 %) and Na₂WO₄ (0, 35 and 70 μg L^-1) concentrations and incubation temperature (15, 25 and 35 °C) on the stoichiometry and kinetics of the methanotrophic consortia was investigated. Consortia enriched from activated sludge at 15 °C accumulated the highest yields of ectoine and hydroxyectoine at 6 % NaCl (105.0 ± 27.2 and 24.2 ± 5.4 mg_extremolyte g_biomass^-1, respectively). The consortia enriched from the salt lagoon accumulated the highest yield of ectoine and hydroxyectoine at 9 % NaCl (56.6 ± 2.5 and 51.0 ± 2.0 mg_extremolyte g_biomass^-1, respectively) at 25 °C. The supplementation of tungsten to the cultivation medium did not impact on the accumulation of ectoines in any of the consortia. A molecular characterization of the enrichments revealed a relative abundance of ectoine-accumulating methanotrophs of 7-16 %, with Methylomicrobium buryatense and Methylomicrobium japanense as the main players in the bioconversion of methane into ectoine.

The diversity of unique 1,4,5,6-Tetrahydro-2-methyl-4-pyrimidinecarboxylic acid coding common genes and Universal stress protein in Ectoine TRAP cluster (UspA) in 32 Halomonas species

OBJECTIVES

To decipher the diversity of unique ectoine-coding housekeeping genes in the genus Halomonas.

RESULTS

In Halomonas, 1,4,5,6-Tetrahydro-2-methyl-4-pyrimidinecarboxylic acid has a crucial role as a stress-tolerant chaperone, a compatible solute, a cell membrane stabilizer, and a reduction in cell damage under stressful conditions. Apart from the current 16S rRNA biomarker, it serves as a blueprint for identifying Halomonas species. Halomonas elongata 1H9 was found to have 11 ectoine-coding genes. The presence of a superfamily of conserved ectoine-coding among members of the genus Halomonas was discovered after genome annotations of 93 Halomonas spp. As a result of the inclusion of 11 single copy ectoine coding genes in 32 Halomonas spp., genome-wide evaluations of ectoine coding genes indicate that 32 Halomonas spp. have a very strong association with H. elongata 1H9, which has been proven evidence-based approach to elucidate phylogenetic relatedness of ectoine-coding child taxa in the genus Halomonas. Total 32 Halomonas species have a single copy number of 11 distinct ectoine-coding genes that help Halomonas spp., produce ectoine under stressful conditions. Furthermore, the existence of the Universal stress protein (UspA) gene suggests that Halomonas species developed directly from primitive bacteria, highlighting its role during the progression of microbial evolution.

New insights into hydroxyectoine synthesis and its transcriptional regulation in the broad-salt growing halophilic bacterium Chromohalobacter salexigens

Elucidating the mechanisms controlling the synthesis of hydroxyectoine is important to design novel genetic engineering strategies for optimizing the production of this biotechnologically relevant compatible solute. The genome of the halophilic bacterium Chromohalobacter salexigens carries two ectoine hydroxylase genes, namely ectD and ectE, whose encoded proteins share the characteristic consensus motif of ectoine hydroxylases but showed only a 51.9% identity between them. In this work, we have shown that ectE encodes a secondary functional ectoine hydroxylase and that the hydroxyectoine synthesis mediated by this enzyme contributes to C.␣salexigens thermoprotection. The evolutionary pattern of EctD and EctE and related proteins suggests that they may have arisen from duplication of an ancestral gene preceding the directional divergence that gave origin to the orders Oceanospirillales and Alteromonadales. Osmoregulated expression of ectD at exponential phase, as well as the thermoregulated expression of ectD at the stationary phase, seemed to be dependent on the general stress factor RpoS. In contrast, expression of ectE was always RpoS-dependent regardless of the growth phase and osmotic or heat stress conditions tested. The data presented here suggest that the AraC-GlxA-like EctZ transcriptional regulator, whose encoding gene lies upstream of ectD, plays a dual function under exponential growth as both a transcriptional activator of osmoregulated ectD expression and a repressor of ectE transcription, privileging the synthesis of the main ectoine hydroxylase EctD. Inactivation of ectZ resulted in a higher amount of the total ectoines pool at the expenses of a higher accumulation of ectoine, with maintenance of the hydroxyectoine levels. In addition to the transcriptional control, our results suggest a strong post-transcriptional regulation of hydroxyectoine synthesis. Data on the accumulation of ectoine and hydroxyectoine in rpoS and ectZ strains pave the way for using these genetic backgrounds for metabolic engineering for hydroxyectoine production.

Observational study investigating Ectoin® Rhinitis Nasal Spray as natural treatment option of acute rhinosinusitis compared to treatment with Xylometazoline

Introduction

Symptomatic relief of acute rhinosinusitis is commonly achieved with nasal decongestants. The current observational study investigated the efficacy and safety of treatment of acute rhinosinusitis with Ectoin^® Rhinitis Spray compared to or in combination with Xylometazoline-containing decongesting nasal spray.

Methods

Patients with acute rhinosinusitis applied either Ectoin^® Rhinitis Spray, Xylometazoline nasal spray or a combination of both products. Rhinosinusitis symptoms were assessed, and nasal oedema and endonasal redness were determined by rhinoscopy. Patient diaries based on the validated SNOT (Sino Nasal Outcome Test) questionnaire evaluated rhinosinusitis parameters over time and influences of the disease on quality of life. Following treatment, investigators and patients judged the efficacy and tolerability.

Results

Ectoin^® Rhinitis Spray diminished common rhinosinusitis symptoms such as nasal obstruction, nasal secretion, facial pain/headache, and smell/taste impairment. Upon treatment over 7 days, rhinosinusitis sum scores decreased statistically significantly (p < 0.001) by − 64.25%, which was comparable to that achieved with Xylometazoline-containing decongesting nasal spray (− 67.60%). No side effects were observed during treatment with Ectoin^® Rhinitis Spray, whereas treatment with Xylometazoline-containing nasal spray resulted in nasal mucosa dryness. Concomitant treatment with both products diminished the development of nasal dryness and required fewer applications of Xylometazoline-containing nasal spray.

Conclusion

Ectoin^® Rhinitis Spray is an effective, natural treatment option for acute rhinosinusitis, which may be used as monotherapy or as add-on treatment with a Xylometazoline-containing nasal spray. The concomitant use of Ectoin^® Rhinitis Spray might reduce the needed dose of decongestant nasal spray and counteract bothersome side effects such as dry nasal mucosa.

Trial registration

The current study was registered in the ClinicalTrials.gov database under the identifier: NCT03693976 (date of registration: Oct 3, 2018).

β-Cyanoalanine Synthase Regulates the Accumulation of β-ODAP via Interaction with Serine Acetyltransferase in Lathyrus sativus

β-N-Oxalyl-l-α,β-diaminopropionic acid (β-ODAP), found in Lathyrus sativus at first, causes a neurological disease, lathyrism, when over ingested in an unbalanced diet. Our previous research suggested that β-ODAP biosynthesis is related to sulfur metabolism. In this study, β-cyanoalanine synthase (β-CAS) was confirmed to be responsible for β-ODAP biosynthesis via in vitro enzymatic analysis. LsCAS was found to be pyridoxal phosphate (PLP)-dependent via spectroscopic analysis and dual functional via enzymatic activity analysis. Generation of a M135T/M235S/S239T triple mutant of LsCAS, which are the key sites to control the ratio of CAS/cysteine synthase (CS) activity, switches reaction chemistry to that of a CS. LsCAS interactions were further screened and verified via Y2H, BiFC and pull-down assay. It was suggested that LsSAT2 interacts and forms a cysteine regulatory complex (CRC) with LsCAS in mitochondria, which improves LsSAT while reduces LsCAS activities to affect β-ODAP content positively. These results provide new insights into the molecular regulation of β-ODAP content in L. sativus.

Food web biomagnification of the neurotoxin β-N-methylamino-L-alanine in a diatom-dominated marine ecosystem in China

The neurotoxin β-N-methylamino-L-alanine (BMAA) reported in some cyanobacteria and eukaryote microalgae is a cause of concern due to its potential risk of human neurodegenerative diseases. Here, BMAA distribution in phytoplankton, zooplankton, and other marine organisms was investigated in Jiaozhou Bay, China, a diatom-dominated marine ecosystem, during four seasons in 2019. Results showed that BMAA was biomagnified in the food web from phytoplankton to higher trophic levels. Trophic magnification factors (TMFs) for zooplankton, bivalve mollusks, carnivorous crustaceans and carnivorous gastropod mollusks were ca. 4.58, 30.1, 42.5, and 74.4, respectively. Putative identification of β-amino-N-methylalanine (BAMA), an isomer of BMAA, was frequently detected in phytoplankton samples. A total of 56 diatom strains of the genera Pseudo-nitzschia, Thalassiosira, Chaetoceros, Planktoniella, and Minidiscus isolated from the Chinese coast were cultured in the laboratory, among which 21 strains contained BMAA mainly in precipitated bound form at toxin concentrations ranging from 0.11 to 3.95 µg/g dry weight. Only 2,4-diaminobutyric acid (DAB) but not BMAA or BAMA was detected in seven species of bacteria isolated from the gut of gastropod Neverita didyma, suggesting that this benthic vector of BMAA may have accumulated this compound via trophic transfer.

[Fingerprinting analysis of non-saponins from water-soluble part and determination of dencichine from Panax notoginseng, P. ginseng and P. quinquefolium based on liquid chromatography coupled with charged aerosol detection]

This work describes the holistic fingerprinting method based on liquid chromatography coupled with charged aerosol detection(CAD) to profile non-saponin from water-soluble parts and determination of dencichine in Panax ginseng(PG), P. quinquefolium(PQ) and P. notoginseng(PNG). Sample extraction was carried out by water with ultra sonication for 30 min, which was eluted by Retain PEP for further analysis. The analysis was performed on a Hypercarb of porous graphitized carbon(3.0 mm×150 mm, 3 μm) column with acetonitrile and 0.1% perfluoropentanoic acid as mobile phase at a flow rate of 0.8 mL·min~(-1). Temperature of evaporator and nitrogen pressure for CAD were set at 50 ℃and 60.1 psi(1 psi≈6.895 kPa), respectively. As a result, dencichine and other polar components had a good performance on resolution and retention. The correlation coefficient(R~2) of dencichine was 0.998 2 in the concentration from 0.019 2 to 0.48 μg·mL~(-1). Limit of quantitation calculated by signal to noise of 10 was 7.4 ng·mL~(-1), and the recovery ranged from 95.52% to 102.7%. Chemical profile of the water-soluble part from PG, PQ and PNG was similar holistically, while the relative content for dencichine and other partial components varied significantly. The proposed method was used for characteristic of chemical profiling for non-saponin from water-soluble part, and determination of dencichine in PG, PQ and PNG.

Production of the neurotoxin beta-N-methylamino-l-alanine may be triggered by agricultural nutrients: An emerging public health issue

Diverse taxa of cyanobacteria, dinoflagellates and diatoms produce β-N-methylamino-l-alanine (BMAA), a non-lipophilic, non-protein amino acid. BMAA is a neurotoxin in mammals. Its ingestion may be linked to human neurodegenerative diseases, namely the Amyotrophic lateral sclerosis/Parkinsonism dementia complex, based on epidemiological evidence from regions where cyanobacterial harmful algal blooms occur frequently. In controlled environments, cyanobacteria produce BMAA in response to ecophysiological cues such as nutrient availability, which may explain the elevated BMAA concentrations in freshwater environments that receive nutrient-rich agricultural runoff. This critical review paper summarizes what is known about how BMAA supports ecophysiological functions like nitrogen metabolism, photosyntheis and provides a competitive advantage to cyanobacteria in controlled and natural environments. We explain how BMAA production affected competitive interactions among the N₂-fixing and non-N₂-fixing populations in a freshwater cyanobacterial bloom that was stimulated by nutrient loading from the surrounding agricultural landscape. Better control of nutrients in agricultural fields is an excellent strategy to avoid the negative environmental consequences and public health concerns related to BMAA production.

A systematic comparison of ectoine production from upgraded biogas using Methylomicrobium alcaliphilum and a mixed haloalkaliphilic consortium

Biogas is the byproduct of anaerobic digestion with the highest valorization potential, however its full exploitation is limited by the lack of tax incentives and the inherent presence of pollutants. The development of technologies for biogas conversion into added-value products is crucial in order to ensure the competitiveness of this bioresource. This study constitutes the first proof of concept of upgraded biogas bioconversion into the high profit margin product ectoine. Ectoine represents the most expensive product synthesized by microorganisms with a retail value of 1000 $ kg^-1 and a yearly increasing demand that currently entails a total market opportunity of 15000 M€. First, the production of ectoine from upgraded biogas was assessed in batch bioreactors. The presence of H₂S did not exert a negative effect on the growth of the haloalkaliphilic ectoine producers, and ectoine yields up to 49 mg g biomass^-1 were obtained. A second experiment conducted in continuous bubble column bioreactors confirmed the feasibility of the process under continuous mode (with ectoine yields of 109 mg g biomass^-1). Finally, this study revealed that the removal of toxic compounds (i.e. medium dilution rate of 0.5 day^-1) and process operation with a consortium composed of methylotrophic/non-methylotrophic ectoine producers enhanced upgraded biogas bioconversion. This research discloses the basis for the application of this innovative technology and could boost the economic performance of anaerobic digestion.

Decomposition of β-N-methylamino-L-alanine (BMAA) and 2,4-diaminobutyric acid (DAB) during chlorination and consequent disinfection byproducts formation

β-N-methylamino-L-alanine (BMAA) and 2,4-diaminobutyric acid (DAB) are two newly identified algal toxins, and they may react with chlorine to undergo decomposition and generate disinfection byproducts (DBPs) during pre-chlorination as well as chlorine disinfection. In this study, the decomposition of BMAA and DAB during chlorination and the consequent DBPs formation were investigated. The BMAA and DAB concentrations in source waters were determined, the decomposition kinetics of BMAA and DAB and the formation of DBPs during chlorination were studied, the formation pathways of DBPs from BMAA and DAB were explored, and the factors which may affect the decomposition and DBPs formation were examined. The results revealed that BMAA and DAB were commonly detected in source waters from Taihu Lake, and the highest level of BMAA reached 230.8 ng/L, while the concentrations of DAB were generally around 2.0 ng/L. The decomposition of BMAA and DAB during chlorination both followed pseudo-first-order decay while the decomposition rate constant of DAB was significantly higher than that of BMAA. Trihalomethanes (THMs), haloacetic acids (HAAs), and haloacetonitriles (HANs) were all generated during the chlorination of BMAA and DAB with relatively high yields. Notably, the THMs, HAAs, and HANs yields of each carbon atom from BMAA and DAB were significantly higher than that from other organic precursors, and the formation of HANs from DAB was significantly higher than that from BMAA. The formation pathways of DBPs from BMAA and DAB were tentatively proposed and verified through theoretical calculations. Of note, the proposed formation pathways of THMs and HAAs from BMAA were similar to that from DAB, while the proposed formation pathways of HANs from BMAA and DAB showed some differences. Chlorine dose, pH and temperature all affected the decomposition of BMAA and DAB and DBPs formation during chlorination.

Ectoine hydroxylase displays selective trans-3-hydroxylation activity towards L-proline

L-Hydroxyproline (Hyp) is a valuable intermediate for the synthesis of pharmaceuticals; consequently, a practical process for its production has been in high demand. To date, industrial processes have been developed by using L-Pro hydroxylases. However, a process for the synthesis of trans-3-Hyp has not yet been established, because of the lack of highly selective enzymes that can convert L-Pro to trans-3-Hyp. The present study was designed to develop a biocatalytic trans-3-Hyp production process. We speculated that ectoine hydroxylase (EctD), which is involved in the hydroxylation of the known compatible solute ectoine, may possess the ability to hydroxylate L-Pro, since the structures of ectoine and 5-hydroxyectoine resemble those of L-Pro and trans-3-Hyp, respectively. Consequently, we discovered that ectoine hydroxylases from Halomonas elongata, as well as some actinobacteria, catalyzed L-Pro hydroxylation to form trans-3-Hyp. Of these, ectoine hydroxylase from Streptomyces cattleya also utilized 3,4-dehydro-L-Pro, 2-methyl-L-Pro, and L-pipecolic acid as substrates. In the whole-cell bioconversion of L-Pro into trans-3-Hyp using Escherichia coli expressing the ectD gene from S. cattleya, only 12.4 mM trans-3-Hyp was produced from 30 mM L-Pro, suggesting a rapid depletion of 2-oxoglutarate, an essential component of enzyme activity as a cosubstrate, in the host. Therefore, the endogenous 2-oxoglutarate dehydrogenase gene was deleted. Using this deletion mutant as the host, trans-3-Hyp production was enhanced up to 26.8 mM from 30 mM L-Pro, with minimal loss of 2-oxoglutarate. This finding is not only beneficial for trans-3-Hyp production, but also for other E. coli bioconversion processes involving 2-oxoglutarate-utilizing enzymes.

Geographical modeling of exposure risk to cyanobacteria for epidemiological purposes

The cyanobacteria-derived neurotoxin β-methylamino-L-alanine (BMAA) represents a plausible environmental trigger for amyotrophic lateral sclerosis (ALS), a debilitating and fatal neuromuscular disease. With the eutrophication of water bodies, cyanobacterial blooms and their toxins are becoming increasingly prevalent in France, especially in the Brittany region. Cyanobacteria are monitored at only a few recreational sites, preventing an estimation of exposure of the human population. By contrast, phosphorus, a limiting nutrient for cyanobacterial growth and thus considered a good proxy for cyanobacteria exposure, is monitored in many but not all surface water bodies. Our goal was to develop a geographic exposure indicator that could be used in epidemiological research. We considered the total phosphorus (TP) concentration (mg/L) of samples collected between October 2007 and September 2012 at 179 monitoring stations distributed throughout the Brittany region. Using readily available spatial data, we computed environmental descriptors at the watershed level with a Geographic Information System. Then, these descriptors were introduced into a backward stepwise linear regression model to predict the median TP concentration in unmonitored surface water bodies. TP concentrations in surface water follow an increasing gradient from West to East and inland to coast. The empirical concentration model included five predictor variables with a fair coefficient of determination (R(2) = 0.51). The specific total runoff and the watershed slope correlated negatively with the TP concentrations (p = 0.01 and p< 10(-9), respectively), whereas positive associations were found for the proportion of built-up area, the upstream presence of sewage treatment plants, and the algae volume as indicated by the Landsat red/green reflectance ratio (p < 0.01, p < 10(-6) and p < 0.01, respectively). Complementing the monitoring networks, this geographical modeling can help estimate TP concentrations at the watershed level, delivering a proxy for cyanobacteria exposure that can be used along with other risk factors in further ALS epidemiologic case-control studies.

β-N-methylamino-l-alanine causes neurological and pathological phenotypes mimicking Amyotrophic Lateral Sclerosis (ALS): the first step towards an experimental model for sporadic ALS

β-N-methylamino-l-alanine (L-BMAA) is a neurotoxic amino acid that has been related to various neurodegenerative diseases. The aim of this work was to analyze the biotoxicity produced by L-BMAA in vivo in rats, trying to elucidate its physiopathological mechanisms and to search for analogies between the found effects and pathologies like Amyotrophic Lateral Sclerosis (ALS). Our data demonstrated that the neurotoxic effects in vivo were dosage-dependent. For evaluating the state of the animals, a neurological evaluation scale was developed as well as a set of functional tests. Ultrastructural cell analysis of spinal motoneurons has revealed alterations both in endoplasmic reticulum and mitochondria. Since GSK3β could play a role in some neuropathological processes, we analyzed the alterations occurring in GSK3β levels in L-BMAA treated rats, we have observed an increase in the active form of GSK3β levels in lumbar spinal cord and motor cerebral cortex. On the other hand, (TAR)-DNA-binding protein 43 (TDP-43) increased in L-BMAA treated animals. Our results indicated that N-acetylaspartate (NAA) declined in animals treated with L-BMAA, and the ratio of N-acetylaspartate/choline (NAA/Cho), N-acetylaspartate/creatine (NAA/Cr) and N-acetylaspartate/choline+creatine (NAA/Cho+Cr) tended to decrease in lumbar spinal cord and motor cortex. This project offers some encouraging results that could help establishing the progress in the development of an animal model of sporadic ALS and L-BMAA could be a useful tool for this purpose.

Alternatives to dimethylsulfoxide for serum-free cryopreservation of human mesenchymal stem cells

Human mesenchymal stem cells (hMSCs) have some favorable characteristics like high plasticity, multilineage differentiation potential, and comparably easy handling in vitro, making them of interest for many clinical and therapeutic approaches including cell therapy. For routine applications, these cells have to be stored over a certain period of time without loss of cell vitality and function. An easy way to preserve cells is to store them at temperatures between -80 degrees C and -196 degrees C (liquid nitrogen). To prevent cells from the damage caused by the cryopreservation process and to achieve high cell recovery and vitality, cryoprotectants are used. Typically dimethylsulfoxide, often in combination with serum, is used as a cryoprotectant. However, for clinical approaches, the use of dimethylsulfoxide and serum in patients is problematic for several reasons. Therefore, the cryopreservation of human mesenchymal stem cells for cell therapeutic applications without dimethylsulfoxide and serum demands investigation. In this work, non-toxic alternatives to dimethylsulfoxide such as glycerol or the compatible solutes, proline and ectoin, were analyzed in a serum-free cryomedium with respect to their cryoprotective properties. Different concentrations of the cryoprotectants (1-10% (w/v) ectoin or proline, respectively, or 5-20% (v/v) glycerol) and certain incubation times (0-60 minutes) were investigated with regard to post-thaw cell vitality and cell growth. Our results showed that, in general, cryopreservation with ectoin led to high post-thaw cell survival of up to 72% whereas after cryopreservation with glycerol and proline, the hMSC cells were completely dead (glycerol) or had only poor cell survival (proline, 22%). Moreover, the morphology of the hMSC cells changed to a large and flat phenotype after cryopreservation with proline. These results indicate that glycerol and proline are not suitable for cryopreservation of hMSC. In contrast, ectoin has the potential to replace dimethylsulfoxide as a cryoprotectant in a serum-free cryomedium.

Creation of novel chiral synthons with enzymes: application to enantioselective synthesis of antibiotics

Retrosynthesis was carried out to generate, from a target molecule, a symmetric diester in the prochiral or meso form. The symmetric diester was subjected to asymmetric hydrolysis with pig liver esterase to create the corresponding chiral half-ester. The chiral half-ester was converted into the target molecule by organic synthesis. Thus, various types of carbapenem antibiotics, negamycin, showdomycin, 6-azapseudouridine, cordycepin, aristeromycin, neplanocin A, and precursors of fortimicin were efficiently synthesized with the desired absolute configuration. The methods for asymmetric synthesis starting from substrates with sigma-symmetry have been extensively developed.

Plastic encapsulation of stabilized Escherichia coli and Pseudomonas putida

Escherichia coli and Pseudomonas putida dried in hydroxyectoine or trehalose are shown to be highly resistant to the organic solvents chloroform and acetone, and consequently, they can be encapsulated in a viable form in solid plastic materials. Bacteria are recovered by rehydration after physical disruption of the plastic. P. putida incorporated into a plastic coating of maize seeds was shown to colonize roots efficiently after germination.

High survival and stability rates of Escherichia coli dried in hydroxyectoine

The tetrahydropyramidine hydroxyectoine acts as an osmolyte in a range of bacterial species, but its use as a desiccation protectant is less well explored. Recently, it was demonstrated that hydroxyectoine provides effective stabilisation of the Gram-negative species Pseudomonas putida, which is only relatively poorly preserved by the better-characterised protectant, trehalose. It is now shown that hydroxyectoine also protects the paradigmatic bacterium, Escherichia coli: osmotically-preconditioned E. coli dried in hydroxyectoine exhibited a high degree of desiccation tolerance, similar to that achieved using trehalose in this species. Hydroxyectoine is apparently accumulated from hypersaline medium in preference to trehalose biosynthesis, but E. coli loaded with hydroxyectoine in this way showed reduced stability in the dry state. This suggests that, although both hydroxyectoine and trehalose perform equally well as extracellular protectants, trehalose is preferred for intracellular protection.

Neurolathyrism: mitochondrial dysfunction in excitotoxicity mediated by L-beta-oxalyl aminoalanine

beta-N-Oxalyl amino-L-alanine (L-BOAA); synonym beta-N-oxalyl-alpha,beta-diaminopropionic acid (beta-ODAP) is a naturally occurring non-protein amino acid present in the chickling pea from the plant Lathyrus sativus grown in drought prone areas. Ingestion of L-BOAA as a staple diet results in a progressive neurodegenerative condition, neurolathyrism, a form of motor neuron disease which affects the upper motor neurons and anterior horn cells of the lumbar spinal cord. L-BOAA is an excitatory acid and acts as an agonist at the AMPA receptor. One of the primary effects of L-BOAA toxicity is the inhibition of mitochondrial complex I selectively in the motor cortex and lumbar spinal cord. Recent evidence has suggested that the mitochondrial dysfunction is a consequence of oxidation protein thiol groups as a result of generation of reactive oxygen species. Mitochondrial complex I is highly to vulnerable to inactivation through oxidation of vital sulfhydryl groups. Thiol antioxidants such as alpha-liopic acid offer a method of protecting mitochondrial function. A common mechanism involving oxidation of protein thiol groups may underlie neurodegeneration occurring through mitochondrial dysfunction induced by excitatory amino acid.

Mutational analysis of the fractalkine chemokine domain. Basic amino acid residues differentially contribute to CX3CR1 binding, signaling, and cell adhesion

Fractalkine (FKN/CX3CL1) is a unique member of the chemokine gene family and contains a chemokine domain (CD), a mucin-like stalk, a single transmembrane region, and a short intracellular C terminus. This structural distinction affords FKN the property of mediating capture and firm adhesion of FKN receptor (CX3CR1)-expressing cells under physiological flow conditions. Shed forms of FKN also exist, and these promote chemotaxis of CX3CR1-expressing leukocytes. The goal of the present study was to identify specific residues within the FKN-CD critical for FKN-CX3CR1 interactions. Two residues were identified in the FKN-CD, namely Lys-7 and Arg-47, that are important determinants in mediating an FKN-CX3CR1 interaction. FKN-K7A and FKN-R47A mutants exhibited 30-60-fold decreases in affinity for CX3CR1 and failed to arrest efficiently CX3CR1-expressing cells under physiological flow conditions. However, these mutants had differential effects on chemotaxis of CX3CR1-expressing cells. The FKN-K7A mutant acted as an equipotent partial agonist, whereas the FKN-R47A mutant had marked decreased potency and efficacy in measures of chemotactic activity. These data identify specific structural features of the FKN-CD that are important in interactions with CX3CR1 including steady state binding, signaling, and firm adhesion of CX3CR1-expressing cells.

Excitotoxicity induces changes in rat brain gangliosides

The patterns of major gangliosides in the rat hippocampi and olfactory bulbs was examined in vivo after microinjections of Ibotenic acid and L-BOAA (NMDA and AMPA receptor agonists, respectively) which were given under free-movement conditions. The excitotoxicity induced by injections of Ibotenic acid promoted transient ganglioside changes in olfactory bulbs and permanent changes in hippocampus. Four days after injections, the amount of gangliosides in the hippocampus increased significantly for GQ1b, GT1b and GD1b and decreased in the olfactory bulb for GQ1b, GT1b, GD1b, GD1a and GM1 compared to normal ganglioside levels. The alterations of gangliosides were minimal 1 day after injections. After 5 weeks, the amounts of GQ1b, GT1b and GD1b dramatically decreased in the hippocampus while in the olfactory bulbs gangliosides recovered to normal levels. The results obtained with L-BOAA 4 days after injections strengthen the results observed in the experiments using Ibotenic acid and corroborate our suggestion that gangliosides have an active role in the compensatory mechanism to maintain the number of glutamate receptors during the excitotoxicity.

Recruitment of a specific amoeboid myosin I isoform to the plasma membrane in chemotactic Dictyostelium cells

The Dictyostelium class I myosins, MyoA, -B, -C, and -D, participate in plasma membrane-based cellular processes such as pseudopod extension and macropinocytosis. Given the existence of a high affinity membrane-binding site in the C-terminal tail domain of these motor proteins and their localized site of action at the cortical membrane-cytoskeleton, it was of interest to determine whether each myosin I was directly associated with the plasma membrane. The membrane association of a myosin I heavy chain kinase that regulates the activity of one of the class I myosins, MyoD was also examined. Cellular fractionation experiments revealed that the majority of the Dicyostelium MyoA, -B, -C and -D heavy chains and the kinase are cytosolic. However, a small, but significant, fraction (appr. 7. -15%) of each myosin I and the kinase was associated with the plasma membrane. The level of plasma membrane-associated MyoB, but neither that of MyoC nor MyoD, increases up to 2-fold in highly motile, streaming cells. These results indicate that Dictyostelium specifically recruits myoB to the plasma membrane during directed cell migration, consistent with its known role in pseudopod formation.

Membrane binding of peptides containing both basic and aromatic residues. Experimental studies with peptides corresponding to the scaffolding region of caveolin and the effector region of MARCKS

We have studied the binding of peptides containing both basic and aromatic residues to phospholipid vesicles. The peptides caveolin(92-101) and MARCKS(151-175) both contain five aromatic residues, but have 3 and 13 positive charges, respectively. Our results show the aromatic residues insert into the bilayer and anchor the peptides weakly to vesicles formed from the zwitterionic lipid phosphatidylcholine (PC). Incorporation of a monovalent acidic lipid (e.g., phosphatidylserine, PS) into the vesicles enhances the binding of both peptides via nonspecific electrostatic interactions. As predicted from application of the Poisson-Boltzmann equation to atomic models of the peptide and membranes, the enhancement is larger (e.g., 10(4)- vs 10-fold for 17% PS) for the more basic MARCKS(151-175). Replacing the five Phe with five Ala residues in MARCKS(151-175) decreases the binding to 10:1 PC/PS vesicles only slightly (6-fold). This result is also consistent with the predictions of our theoretical model: the loss of the attractive hydrophobic energy is partially compensated by a decrease in the repulsive Born/desolvation energy as the peptide moves away from the membrane surface. Incorporating multivalent phosphatidylinositol 4, 5-bisphosphate (PIP(2)) into PC vesicles produces dramatically different effects on the membrane binding of the two peptides: 1% PIP(2) enhances caveolin(92-101) binding only 3-fold, but increases MARCKS(151-175) binding 10(4)-fold. The strong interaction between the effector region of MARCKS and PIP(2) has interesting implications for the cellular function of MARCKS.

SH3 domain recognition of a proline-independent tyrosine-based RKxxYxxY motif in immune cell adaptor SKAP55

Src-homology 3 (SH3) domains recognize PXXP core motif preceded or followed by positively charged residue(s). Whether SH3 domains recognize motifs other than proline-based sequences is unclear. In this study, we report SH3 domain binding to a novel proline-independent motif in immune cell adaptor SKAP55, which is comprised of two N-terminal lysine and arginine residues followed by two tyrosines (i.e. RKxxYxxY). Domains capable of binding to class I proline motifs bound to the motif, while the class II domains failed to bind. Peptide precipitation, alanine scanning and in vivo co-expression studies demonstrated a requirement for the arginine, lysine and tandem tyrosines of the motif. Two-dimensional NMR analysis of the peptide bound FYN-SH3 domain showed overlap with the binding site of a proline-rich peptide on the charged surface of the SH3 domain, while resonance signals for other residues (W119, W120, Y137) were not perturbed by the RKGDYASY based peptide. Expression of the RKGDYASY peptide potently inhibited TcRzeta/CD3-mediated NF-AT transcription in T cells. Our findings extend the repertoire of SH3 domain binding motifs to include a tyrosine-based motif and demonstrate a regulatory role for this motif in receptor signaling.

Differential effect of beta-N-oxalylamino-L-alanine, the Lathyrus sativus neurotoxin, and (+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate on the excitatory amino acid and taurine levels in the brain of freely moving rats

We studied the effect of beta-oxalylamino-L-alanine, a glutamate analog present in Lathyrus sativus seeds and implicated in the etiopathogenesis of neurolathyrism, and (+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate on the extracellular levels of aspartate, glutamate and taurine in the primary motor cortex of freely moving rats. We found that while both neurotoxins increase the level of aspartate and glutamate, only (+/-)-alpha(-amino-3-hydroxy-5-methylisoxazole-4-propionate is able to modulate the level of taurine. GYKI-52466, a non-competitive non-NMDA antagonist, inhibited beta-oxalylamino-L-alanine-induced increase of aspartate, but not that of glutamate. Conversely, this antagonist proved to be very efficient in blocking the stimulating effect of (+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate on all three amino acids. We suggest that beta-oxalylamino-L-alanine increases the level of glutamate in vivo by a mechanism not connected to its effect on the non-NMDA receptors, which might involve the inhibition of glutamate transport. This would allow the excitatory neurotransmitter to reach a concentration sufficient to stimulate the non-NMDA receptors, which in their turn mediate the specific release of aspartate. Although the role of aspartate as a neurotransmitter is still under discussion, it might indeed amplify the excitotoxic cascade through its action on NMDA receptors. We speculate that this sequence of events might represent an important step in the molecular cascade leading to the appearance of the selective motoneuron degeneration in neurolathyrism.

Characterization of a heparin binding site on the heavy chain of factor XI

The glycosaminoglycan heparin enhances several reactions involving coagulation factor XI (FXI) including activation of FXI by factor XIIa, thrombin, and autoactivation; and inactivation of activated FXI (FXIa) by serine protease inhibitors. We examined the effect of heparin on inhibition of FXIa by the inhibitors C1-inhibitor (C1-INH) and antithrombin III (ATIII). Second order rate constants for inhibition in the absence of heparin were 1.57 x 10(3) and 0.91 x 10(3) M-1 s-1 for C1-INH and ATIII, respectively. Therapeutic heparin concentrations (0.1-1.0 units/ml) enhanced inhibition by ATIII 20-55-fold compared with 0.1-7.0-fold for C1-INH. For both inhibitors, the effect of heparin over a wide range of concentrations (10(-1) to 10(5) units/ml) produced bell-shaped curves, demonstrating that inhibition occurs by a template mechanism requiring both inhibitor and protease to bind to heparin. This implies that FXI/XIa contains structural elements that interact with heparin. Human FXI contains a sequence of amino acids (R250-I-K-K-S-K) in the apple 3 domain of the heavy chain that binds heparin (Ho, D., Badellino, K., Baglia, F., and Walsh, P. (1998) J. Biol. Chem. 273, 16382-16390). To determine the importance of this sequence to heparin-mediated reactions, recombinant FXI molecules with alanine substitutions for basic amino acids were expressed in 293 fibroblasts, and tested in heparin-dependent assays. Inhibition of FXIa by ATIII in the presence of heparin was decreased 4-fold by alanine substitution at Lys253 (A253), with smaller effects noted for mutants A255 and A252. FXI undergoes autoactivation to FXIa in the presence of heparin. The rate of autoactivation was decreased substantially for A253 with modest decreases for A255 and A252. Substituting all four charged residues in the sequence resulted in a profound decrease in autoactivation, significantly greater than for any single substitution. Relative affinity for heparin was tested by determining the concentration of NaCl required to elute FXIa from heparin-Sepharose. Wild type FXIa eluted from the column at 320 mM NaCl, whereas FXIa with multiple substitutions (A252-254 or A250-255) eluted at 230 mM NaCl. All proteins with single substitutions in charged amino acids eluted at intermediate NaCl concentrations. The data indicate that FXI/XIa must bind to heparin for optimal inhibition by ATIII and for autoactivation. Lys253 is the most important amino acid involved in binding, and Lys255 and Lys252 also have roles in interactions with heparin.

Leukaemia inhibitory factor (LIF) production in a mouse model of spinal trauma

A model of spinal trauma was developed where spinal neurones of adult mice were exposed to the excitotoxic glutamate analogue beta-N-oxylamino-L-alanine (L-BOAA). After 24 h, the injured neurones received a single dose of [125I]-LIF at the same site of the spinal cord, and 2 h later, tissues were removed to assess the distribution of leukaemia inhibitory factor (LIF). There was a significant increase in LIF binding to the injured region of the spinal cord over saline controls, and this corresponded with a significant increase in LIF mRNA expression in the same region of the cord. There was a change in the expression of ciliary neurotrophic factor, but the expression of cardiotrophin-1 (CT-1) and the common receptor subunit LIF receptor beta (LIFRbeta) did not change after neurotoxin treatment. The results add to the evidence that LIF plays a significant role in the response of adult neuronal tissue to injury.

Apoptosis induced by beta-N-oxalylamino-L-alanine on a motoneuron hybrid cell line

It has been suggested that beta-N-oxalylamino-L-alanine, a non-protein amino acid present in the Lathyrus Sativus seeds, may play a role in the etiopathogenesis of neurolathyrism, a toxic form of motor neuron disease clinically characterized by a severe spastic paraparesis. In order to investigate the mechanisms of beta-N-oxalylamino-L-alanine-mediated cell death, we studied the effect of this neurotoxin as well as other excitatory amino acids agonists on the growth and survival of motoneuron hybrid ventral spinal cord 4.1 cells. beta-N-oxalylamino-L-alanine was toxic to ventral spinal cord 4.1 cells in a concentration-dependent fashion (0.5-10 mM). Among the excitatory amino acids tested, only glutamate (1-10 mM), quisqualate (1 mM) and, with less extent, beta-N-methylamino-L-alanine (10 mM) induced a significant reduction of cell survival. The effect of Lathyrus Sativus neurotoxin was a slow process, becoming apparent only after 24-48 h of incubation. Interestingly, a mathematical analysis applied to the time course and dose curve of beta-N-oxalylamino-L-alanine toxicity suggested that even for very low concentrations of the amino acid it is theoretically possible to predict a time-dependent effect. The cell death was not blocked by antagonists of N-methyl-D-aspartate or non-N-methyl-D-aspartate receptors; aurintricarboxylic acid and alpha-tocopherol gave a partial protection; cysteine (1 mM) prevented the toxic effect of both Lathyrus Sativus neurotoxin and glutamate as well as quisqualate. Morphologically, in the presence of either beta-N-oxalylamino-L-alanine, glutamate or quisqualate, ventral spinal cord 4.1 cells showed apoptotic features also confirmed by ISEL technique and agarose gel electrophoresis of genomic DNA. Thus, our results suggest that in ventral spinal cord 4.1 motoneuron hybrid cells, in the absence of functional synaptic excitatory amino acid receptors, beta-N-oxalylamino-L-alanine induces cell degeneration through an apoptotic mechanism, possibly mediated by a block of cystine/glutamate Xc antiporter.

Action of beta-N-oxalylamino-L-alanine on mouse brain NADH-dehydrogenase activity

beta-N-Oxalylamino-L-alanine (L-BOAA), a non-protein neuroexcitatory amino acid present in the seeds of Lathyrus sativus (chickling or grass pea), is known to produce its neurotoxic effects by overstimulation of non-N-methyl-D-aspartate receptors, especially alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors, at micromolar concentrations. It has recently been reported that L-BOAA selectively inhibits mitochondrial enzyme NADH-dehydrogenase (NADH-DH) in brain slices at subpicomolar concentrations. The present study finds that up to 4 mM concentrations of pure L-BOAA fail to inhibit NADH-DH activity in mouse brain homogenate and isolated brain mitochondria. Two known inhibitors (rotenone and 1-methyl-4-phenylpyridinium ion, MPP+) of this mitochondrial enzyme produced significant inhibition under identical conditions. NADH-DH inhibition was also not observed in the homogenate or mitochondria from the brains of animals systemically treated with convulsive doses of L-BOAA. Some inhibition (20-37%) of NADH-DH activity was observed in mouse brain slices incubated with 100-1,000 microM concentrations of L-BOAA for 1 h at 37 degrees C in an atmosphere of 95% O2 and 5% CO2, but the inhibition was nonselective, because the activity of another mitchondrial enzyme, succinic dehydrogenase, was similarly inhibited by L-BOAA. These results are in contrast with the report that L-BOAA inhibits mitochondrial NADH-DH selectively at subpicomolar concentrations. We suggest the observed nonselective NADH-DH inhibition in mouse brain slices treated with L-BOAA is caused by neuronal damage through an excitotoxic mechanism.

Regional differences in the interaction of the excitotoxins domoate and L-beta-oxalyl-amino-alanine with [3H]kainate binding sites in human hippocampus

The excitotoxic amino acid domoate causes anterograde amnesia and memory deficits while the excitotoxin L-beta-oxalyl-amino-alanine (L-BOAA) is considered the causative agent of the motoneurone disorder, neurolathyrism. Employing quantitative autoradiography we investigated the potency of domoate and L-BOAA to inhibit [3H]kainate binding in human hippocampus. Domoate inhibited binding of [3H]kainate with inhibition constants between 5.8 +/- 2.8 nM (deep layers of gyrus parahippocampalis) and 200.9 +/- 247.8 nM (CA1 region of hippocampus). It was about a thousandfold more potent than L-BOAA with inhibition constants between 2.1 +/- 0.5 microM (superficial layers of gyrus parahippocampalis) and 51.0 +/- 41.9 microM (CA2/3 region of hippocampus). Interestingly, L-BOAA showed lowest affinity to [3H]kainate binding sites in those regions in which domoate showed highest affinity (e.g. CA2/3) and vice versa (e.g. CA1). These data further support the notion that the neurological symptoms observed after domoate intoxication are due to an excitotoxic action at kainate receptors and provide evidence for heterogeneity of kainate receptors in human hippocampus.