Maintaining Membrane Integrity Research Articles

Identification of Novel phoP-phoQ Regulated Genes that Contribute to Polymyxin B Tolerance in Pseudomonas aeruginosa

Polymyxin B and E (colistin) are the last resorts to treat multidrug-resistant Gram-negative pathogens. Pseudomonas aeruginosa is intrinsically resistant to a variety of antibiotics. The PhoP-PhoQ two-component regulatory system contributes to the resistance to polymyxins by regulating an arnBCADTEF-pmrE operon that encodes lipopolysaccharide modification enzymes. To identify additional PhoP-regulated genes that contribute to the tolerance to polymyxin B, we performed a chromatin immunoprecipitation sequencing (ChIP-Seq) assay and found novel PhoP binding sites on the chromosome. We further verified that PhoP directly controls the expression of PA14_46900, PA14_50740 and PA14_52340, and the operons of PA14_11970-PA14_11960 and PA14_52350-PA14_52370. Our results demonstrated that mutation of PA14_46900 increased the bacterial binding and susceptibility to polymyxin B. Meanwhile, mutation of PA14_11960 (papP), PA14_11970 (mpl), PA14_50740 (slyB), PA14_52350 (ppgS), and PA14_52370 (ppgH) reduced the bacterial survival rates and increased ethidium bromide influx under polymyxin B or Sodium dodecyl sulfate (SDS) treatment, indicating roles of these genes in maintaining membrane integrity in response to the stresses. By 1-N-phenylnaphthylamine (NPN) and propidium iodide (PI) staining assay, we found that papP and slyB are involved in maintaining outer membrane integrity, and mpl and ppgS-ppgH are involved in maintaining inner membrane integrity. Overall, our results reveal novel PhoP-PhoQ regulated genes that contribute to polymyxin B tolerance.

Salicylic acid retards senescence and makes flowers last longer in Nicotiana plumbaginifolia (Viv)

Salicylic acid (SA) is known to be a plant signalling molecule that plays an important role in growth, development and defence response in plants. During the present study the effect of exogenous application of SA on the senescence of cut Nicotiana plumbaginifolia flowers was investigated. The buds were subjected to different concentrations (0.05, 0.1, 0.15, 0.20 and 0.25 mM) of SA. A separate set of flowers kept in distilled water designated the control. The flowers treated with various concentrations of SA resulted in improved flower longevity besides maintaining higher membrane stability index, soluble proteins and sugar fractions. SA treatment decreased the α-amino acid, total phenol content, lipid peroxidase and lipoxygenase activity. The flowers treated with SA showed a significant increase in activity of antioxidant enzymes like superoxide dismutase, catalase and ascorbate peroxidase. Among various concentrations used, 0.05 mM SA was found to be most effective in enhancing the flower longevity. Thus, exogenous SA could maintain membrane integrity by increasing antioxidant system activity, thereby retarding the senescence of cut N. plumbaginifolia flowers.

The lipoprotein NlpD in Cronobacter sakazakii responds to acid stress and regulates macrophage resistance and virulence by maintaining membrane integrity

ABSTRACT Cronobacter sakazakii, an emerging opportunistic pathogen, is implicated in severe foodborne outbreak infections in premature and full-term infants. Generally, acid tolerance is vital for the pathogenesis of foodborne pathogens; however, its role in C. sakazakii virulence remains largely unknown. To screen out acid-tolerance determinants from transposon mutants, anovel counterselection method using gentamicin and acid was developed. Using the counterselection method and growth assay, we screened several acid-sensitive mutants and found that nlpD encodes an acid-resistance factor in C. sakazakii. Compared to the wild-type strain, the nlpD mutant exhibited attenuated virulence in a rat model. Using macrophage THP-1 cells and a pH probe, we verified that nlpD enables bacteria to resist macrophages by resisting acidification. Finally, we confirmed that nlpD maintains C. sakazakii membrane integrity in acid using propidium iodide permeabilization assays via flow cytometry. Our results confirm that nlpD is a novel virulence factor that permits C. sakazakii to survive under acid stress conditions. Considering that NlpD is a conserved lipoprotein located in the bacterial outer membrane, NlpD could be used as a target for drug development.

The Glyoxylate-Serine Pathway Enables Conversion of <i>Saccharomyces cerevisiae</i> to a Synthetic Methylotroph

Methanol represents a promising one-carbon substrate for high-value biochemicals and biofuels production. However, reprogramming a non-methylotrophic industrial host, such as Saccharomyces cerevisiae, to grow in minimal medium with methanol as sole carbon source is challenging. Here, a thermodynamic-based module-circuits (TMC) strategy followed by an adaptive laboratory evolution was adopted to engineer S. cerevisiae to efficiently utilize methanol in minimal medium. Through genome sequencing and reverse engineering, we found that the protein Shm2, involved in the glyoxylate-based serine (gSerine) pathway, plays a crucial role by reducing cytoplasmic accumulation of formaldehyde/formic acid. Through transcriptome and experimental validation, we identified that the ergosterol biosynthesis pathway was upregulated and the metabolites squalene and ergosterol were improved in our evolved strain, which were assumed to rescue cell in methanol medium by maintaining membrane integrity. Our results demonstrate that S. cerevisiae can be exploited as a promising one-carbon (C1) platform for biochemicals or biofuels production.

Water Stress Response in Different <i>Jatropha curcas</i> Accessions from Different Geographical Zones of Botswana: Biochemical & Physiological Perceptive

Jatropha curcas L. is one climate smart drought-resistant multipurpose plant with a variety of properties that have conjured interest all over the world due to its potential to produce biofuel. In this study, Jatropha curcas accessions were collected from three different climate zones of Botswana; Northern region (Maun), Central region (Mmadinare) and Southern region (Thamaga). These accessions were subjected to water stress to study their biochemical and physiological responses. Results showed that water stress increased malondialdehyde (MDA) content, electrolyte leakage as well as proline content in all the accessions. It is worth-noting that Maun accession exhibited highest proline content, when subjected to water stress. Maun accession also displayed less MAD and electrolyte leakage than the other two accessions, an indication of less perturbation to membranes under water stress. This could be attributed in part, to its higher catalase and superoxide dismutase contents, which presumably prevented lipid peroxidation by mopping up reactive oxygen species. The slightly higher dry weights exhibited by Mmadinare and Maun accessions could be ascribed to their ability to maintain membrane integrity under water stress conditions. It can therefore be concluded that Maun and Mmadinare accessions can be grown under drought conditions commonly experienced in Botswana.

Enzymatic Analysis of Yeast Cell Wall-Resident GAPDH and Its Secretion.

In yeast, many proteins are found in both the cytoplasmic and extracellular compartments, and consequently it can be difficult to distinguish nonconventional secretion from cellular leakage. Therefore, we monitored the extracellular glyceraldehyde-3-phosphate dehydrogenase (GAPDH) activity of intact cells as a specific marker for nonconventional secretion. Extracellular GAPDH activity was proportional to the number of cells assayed, increased with incubation time, and was dependent on added substrates. Preincubation of intact cells with 100 μM dithiothreitol increased the reaction rate, consistent with increased access of the enzyme after reduction of cell wall disulfide cross-links. Such treatment did not increase cell permeability to propidium iodide, in contrast to effects of higher concentrations of reducing agents. An amine-specific membrane-impermeant biotinylation reagent specifically inactivated extracellular GAPDH. The enzyme was secreted again after a 30- to 60-min lag following the inactivation, and there was no concomitant increase in propidium iodide staining. There were about 4 × 104 active GAPDH molecules per cell at steady state, and secretion studies showed replenishment to that level 1 h after inactivation. These results establish conditions for specific quantitative assays of cell wall proteins in the absence of cytoplasmic leakage and for subsequent quantification of secretion rates in intact cells.IMPORTANCE Eukaryotic cells secrete many proteins, including many proteins that do not follow the classical secretion pathway. Among these, the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is unexpectedly found in the walls of yeasts and other fungi and in extracellular space in mammalian cell cultures. It is difficult to quantify extracellular GAPDH, because leakage of just a little of the very large amount of cytoplasmic enzyme can invalidate the determinations. We used enzymatic assays of intact cells while also maintaining membrane integrity. The results lead to estimates of the amount of extracellular enzyme and its rate of secretion to the wall in intact cells. Therefore, enzyme assays under controlled conditions can be used to investigate nonconventional secretion more generally.

Phenylalanine Alleviates Postharvest Chilling Injury of Plum Fruit by Modulating Antioxidant System and Enhancing the Accumulation of Phenolic Compound

SUMMARYResearch backgroundLow temperature storage causes chilling injury in plum (Prunus domestica L.) fruits. Consequently, any treatments with beneficial effects against these symptoms would achieve attention. For this purpose, phenylalanine treatments were applied on ‘Stanley’ plum fruits. The main purpose of the present study is to investigate the influence of the exogenous application of phenylalanine on fruit quality, chilling tolerance, and antioxidant capacity of ‘Stanley’ plums during cold storage.Experimental approachPhenylalanine at different concentrations was applied on ‘Stanley’ plums. Following phenylalanine application, plums were cold stored. Chilling injury, antioxidant capacity, electrolyte leakage, malondialdehyde, proline and internal contents of anthocyanin, flavonoids, phenols, ascorbic acid and some antioxidant enzymes were assessed.Results and conclusionsPhenylalanine treatment significantly alleviated chilling injury in plum fruits by enhancing antioxidant capacity and increasing the activity of phenylalanine ammonia lyase enzyme (PAL). Phenylalanine-treated fruits had higher mass fractions of ascorbic acid, anthocyanins, flavonoids and phenols, as well as a higher total antioxidant activity than the control fruits during low temperature storage. Phenylalanine at 7.5 mM was the most effective treatment in enhancing the activity of PAL, the accumulation of phenolic compounds and in reducing the severity of chilling injury. Treatments delayed mass loss and maintained fruit firmness. In addition, the application of 7.5 mM phenylalanine improved the activities of antioxidant enzymes (superoxide dismutase, catalase and ascorbate peroxidase), decreased the accumulation of hydrogen peroxide, and increased the endogenous content of proline. Moreover, phenylalanine maintained membrane integrity, manifested by a reduced electrolyte leakage and malondialdehyde accumulation.Novelty and scientific contributionIn the current study, chilling injury had a positive correlation with the activities of PAL and antioxidant enzymes. However, negative correlations were observed between the chilling injury and ascorbic acid mass fraction, and antioxidant capacity. Considering the results, phenylalanine treatment could be an encouraging approach to alleviate the severity of chilling injury and thus preserve nutritional quality of plums during low temperature storage.

Regulation of ROS Metabolism in Plants under Environmental Stress: A Review of Recent Experimental Evidence.

Various environmental stresses singly or in combination generate excess amounts of reactive oxygen species (ROS), leading to oxidative stress and impaired redox homeostasis. Generation of ROS is the obvious outcome of abiotic stresses and is gaining importance not only for their ubiquitous generation and subsequent damaging effects in plants but also for their diversified roles in signaling cascade, affecting other biomolecules, hormones concerning growth, development, or regulation of stress tolerance. Therefore, a good balance between ROS generation and the antioxidant defense system protects photosynthetic machinery, maintains membrane integrity, and prevents damage to nucleic acids and proteins. Notably, the antioxidant defense system not only scavenges ROS but also regulates the ROS titer for signaling. A glut of studies have been executed over the last few decades to discover the pattern of ROS generation and ROS scavenging. Reports suggested a sharp threshold level of ROS for being beneficial or toxic, depending on the plant species, their growth stages, types of abiotic stresses, stress intensity, and duration. Approaches towards enhancing the antioxidant defense in plants is one of the vital areas of research for plant biologists. Therefore, in this review, we accumulated and discussed the physicochemical basis of ROS production, cellular compartment-specific ROS generation pathways, and their possible distressing effects. Moreover, the function of the antioxidant defense system for detoxification and homeostasis of ROS for maximizing defense is also discussed in light of the latest research endeavors and experimental evidence.

Stringent Response Regulates Stress Resistance in Cyanobacterium Microcystis aeruginosa.

Cyanobacterial blooms are serious environmental issues in global freshwater ecosystems. Nitrogen limitation is one of the most important strategies to control cyanobacterial blooms. However, recent researches showed that N limitation does not effectively control the bloom; oppositely, N limitation induces N-fixing cyanobacterial blooms. The mechanism underlying this ecological event is elusive. In this study, we found that N limitation enhances stress tolerance of Microcystis aeruginosa by triggering stringent response (SR), one of the most important bacterial adaptive responses to environmental stresses. Initiation of SR exerted protective effects on the cells against salt and oxidative stresses by promoting colony formation, maintaining membrane integrity, increasing photosynthetic performance, reducing ROS production, upregulating stress-related genes, etc. These protections possibly help M. aeruginosa maintain their population number during seasonal N limitation. As SR has been proven to be involved in nitrogen fixing under N limitation conditions, the potential role of SR in driving the shift and succession of cyanobacterial blooms was discussed. Our findings provide cellular evidence and possible mechanisms that reducing N input is ineffective for bloom control.

An OsNAM gene plays important role in root rhizobacteria interaction in transgenic Arabidopsis through abiotic stress and phytohormone crosstalk.

Overexpression of Bacillus amyloliquefaciens SN13-responsive OsNAM gene in Arabidopsis reveals its important role in beneficial plant and plant growth promoting rhizobacteria interaction by conferring stress tolerance and phytohormone modulation. Salinity is one of the major constraints that affect crop development and yield. Plants respond and adapt to salt stress via complex mechanisms that involve morpho-physiological, biochemical, and molecular changes. The expression of numerous genes is known to alter during various abiotic stresses and impart stress tolerance. Recently, some known rhizospheric microbes have also been used to mitigate the effects of abiotic stresses; however, the molecular basis of such interactions remains elusive. Therefore, the present investigation was aimed to elucidate the plant growth-promoting rhizobacteria (PGPR; Bacillus amyloliquefaciens-SN13) -induced crosstalk among salinity and phytohormones in OsNAM-overexpressed Arabidopsis plants. Transgenic plants showed increased germination percentage compared to wild-type (WT) seeds under 100mM of NaCl. Phenotypic data showed increased root length, rosette diameter, leaf size, and biomass in transgenics than WT plants. Transgenic plants can also better maintain membrane integrity and osmolyte concentration under salinity as compared to WT. Further, gene expression analysis of AP2/ERF, GST, ERD4, and ARF2 genes showed differential expression and their positive modulation in transgenic Arabidopsis exposed to salt stress in the presence of SN13 as compared to uninoculated WT. Modulation in IAA, ABA, and GA content in inoculated plants showed the more pronounced positive effects of SN13 on transgenic plants that supported our findings on Arabidopsis-SN13 interaction. Overall, the study concludes that SN13 positively modulated expression of stress-responsive genes under salinity and alter phytohormones levels in OsNAM-overexpressed plants suggesting its extensive role in cross-talk among salinity and phytohormones in response to PGPR.

Preparation and Characterization of Dog Erythrocytic Membrane Antigen

Dog erythrocytic membrane antigen plays a major role for determining blood group. Structural and molecular characterization of erythrocytic membrane antigen improves the production of blood typing antisera, to study the auto antibody production in canine autoimmune haemolyticanemia. The proteins in the lipid domain arranged from the inside of the erythrocyte to the outside. The integral membrane proteins include membrane protein 3 visible in coomassie Brilliant blue-stained polyacrylamide gels. The erythrocyte cytoskeleton consists of spectrin, ankyrin, actin, and protein 4.1 form a filamentous network under the lipid bilayer of erythroctic membrane. The cytoskeletal proteins interact with integral proteins and lipids of the bilayer forms network for maintaining membrane integrity. The external clustering of membrane protein 3 creates a recognition site for auto antibodies. The auto antibodies from the erythrocytes of dogs with acute immune haemolytic anemia have similar electrophoretic mobility to the human erythrocyte Rh related proteins and glycoproteins and able to immunoprecipitate membrane proteins that on SDS-PAGE and western blotting. The DEA 1 blood group system consists of antigens 1.1, 1.2, 1.3 which are most significant in terms of transfusion reactions and alloantibodies produced against DEA 3, 5 and 7 are not much clinical significance. Blood samples collected from registered donor dogs and RBC membrane were isolated by hypotonic freeze thaw method. The ghost membrane and cytoplasmic marker were identified in western blot.

Lysosome Fusion Maintains Phagosome Integrity during Fungal Infection

Phagosomes must maintain membrane integrity to exert their microbicidal function. Some microorganisms, however, survive and grow within phagosomes. In such instances, phagosomes must expand to avoid rupture and microbial escape. We studied whether phagosomes regulate their size to preserve integrity during infection with the fungal pathogen Candida albicans. Phagosomes release calcium as C. albicans hyphae elongate, inducing lysosome recruitment and insertion, thereby increasing the phagosomal surface area. As hyphae grow, the expanding phagosome consumes the majority of free lysosomes. Simultaneously, lysosome biosynthesis is stimulated by activation of TFEB, a transcriptional regulator of lysosomal biogenesis. Preventing lysosomal insertion causes phagosomal rupture, NLRP3 inflammasome activation, IL-1β secretion and host-cell death. Whole-genome transcriptomic analysis demonstrate that stress responses elicited in C. albicans upon engulfment are reversed if phagosome expansion is prevented. Our findings reveal a mechanism whereby phagosomes maintain integrity while expanding, ensuring that growing pathogens remain entrapped within this microbicidal compartment.

Root system architecture, physiological analysis and dynamic transcriptomics unravel the drought-responsive traits in rice genotypes

Drought is the major abiotic factors that limit crop productivity worldwide. To withstand stress conditions, plants alter numerous mechanisms for adaption and tolerance. Therefore, in the present study, 106 rice varieties were screened for drought tolerance phenotype via exposing different concentrations of polyethylene glycol 6000 (PEG) in the hydroponic nutrient medium at the time interval of 1, 3, and 7 days to evaluate the changes in their root system architecture. Further, based on root phenotype obtained after PEG-induced drought, two contrasting varieties drought-tolerant Heena and -sensitive Kiran were selected to study transcriptional and physiological alterations at the same stress durations. Physiological parameters (photosynthesis rate, stomatal conductance, transpiration), and non-enzymatic antioxidants (carotenoids, anthocyanins, total phenol content) production indicated better performance of Heena than Kiran. Comparatively higher accumulation of carotenoid and anthocyanin content and the increased photosynthetic rate was also observed in Heena. Root morphology (length, numbers of root hairs, seminal roots and adventitious roots) and anatomical data (lignin deposition, xylem area) enable tolerant variety Heena to better maintain membrane integrity and relative water content, which also contribute to comparatively higher biomass accumulation in Heena under drought. In transcriptome profiling, significant drought stress-associated differentially expressed genes (DEGs) were identified in both the varieties. A total of 1033 and 936 uniquely upregulated DEGs were found in Heena and Kiran respectively. The significant modulation of DEGs that were mainly associated with phytohormone signaling, stress-responsive genes (LEA, DREB), transcription factors (TFs) (AP2/ERF, MYB, WRKY, bHLH), and genes involved in photosynthesis and antioxidative mechanisms indicate better adaptive nature of Heena in stress tolerance. Additionally, the QTL-mapping analysis showed a very high number of DEGs associated with drought stress at AQHP069 QTL in Heena in comparison to Kiran which further distinguishes the drought-responsive traits at the chromosomal level in both the contrasting varieties. Overall, results support the higher capability of Heena over Kiran variety to induce numerous genes along with the development of better root architecture to endure drought stress.

Free-Radical-Mediated Formation of Trans-Cardiolipin Isomers, Analytical Approaches for Lipidomics and Consequences of the Structural Organization of Membranes.

Free-radical-mediated processes, such as peroxidation, isomerization and hydrogenation affecting fatty acid integrity and biological functions, have a trans-disciplinary relevance. Cardiolipins (CL, (1,3-diphosphatidyl-sn-glycerol)) and tetra-linoleoyl-CL are complex phospholipids, exclusively present in the Inner Mitochondrial Membrane (IMM) lipids, where they maintain membrane integrity and regulate enzyme functionalities. Peroxidation pathways and fatty acid remodeling are known causes of mitochondrial disfunctions and pathologies, including cancer. Free-radical-mediated isomerization with the change of the cis CL into geometrical trans isomers is an unknown process with possible consequences on the supramolecular membrane lipid organization. Here, the formation of mono-trans CL (MT-CL) and other trans CL isomers (T-CL) is reported using CL from bovine heart mitochondria and thiyl radicals generated by UV-photolysis from 2-mercaptoethanol. Analytical approaches for CL isomer separation and identification via 1H/13C NMR are provided, together with the chemical study of CL derivatization to fatty acid methyl esters (FAME), useful for lipidomics and metabolomics research. Kinetics information of the radical chain isomerization process was obtained using γ-irradiation conditions. The CL isomerization affected the structural organization of membranes, as tested by the reduction in unilamellar liposome diameter, and accompanied the well-known process of oxidative consumption induced by Fenton reagents. These results highlight a potential new molecular modification pathway of mitochondrial lipids with wide applications to membrane functions and biological consequences.

Postharvest application of L‐cysteine to prevent enzymatic browning of “Stanley” plum fruit during cold storage

Low temperature (1°C) storage causes internal browning (IB) in plum (Prunus domestica L.) fruit. Consequently, any treatment with beneficial effect on decreasing these symptoms would achieve promising attention. For this purpose, L-cysteine (0.1, 0.2, and 0.5%) treatments were applied on “Stanley” plum, and investigated IB, antioxidant capacity, electrolyte leakage (EL), malondialdehyde (MDA), internal content of anthocyanin, flavonoids, phenols, and ascorbic acid and some antioxidant enzymes. The results showed that L-cysteine at 0.5% concentration could significantly alleviate IB in plum fruit by enhancing antioxidant capacity and inhibiting polyphenol oxidase activities. In addition, 0.2 and 0.5% L-cysteine improved the activity of antioxidant enzymes (i.e., superoxide dismutase, catalase, and ascorbate peroxidase) and decreased hydrogen peroxide content. Moreover, L-cysteine maintained membrane integrity as manifested by reduced EL and MDA accumulation. L-cysteine-treated fruit showed higher ascorbic acid, anthocyanin, flavonoids, and phenol contents, and total antioxidant activity higher than the control fruit during low temperature storage. In conclusion, L-cysteine postharvest treatment could act as promising and safe method for preserving nutritional quality of plum during low temperature storage. Practical applications Low temperature storage is considered as an effective way to slow down respiration and senescence processes and then extending the postharvest life of plum. However, low temperature storage results in chilling injury (e.g., IB) and causes requisite of complementary treatment(s) to reduce the injury. Considering the present results, L-cysteine treatment could be spotted as an encouraging approach to reduce browning and preserve nutritional quality of plum during low temperature storage.

TOR complex 2 (TORC2) signaling and the ESCRT machinery cooperate in the protection of plasma membrane integrity in yeast

The endosomal sorting complexes required for transport (ESCRT) mediate evolutionarily conserved membrane remodeling processes. Here, we used budding yeast (Saccharomyces cerevisiae) to explore how the ESCRT machinery contributes to plasma membrane (PM) homeostasis. We found that in response to reduced membrane tension and inhibition of TOR complex 2 (TORC2), ESCRT-III/Vps4 assemblies form at the PM and help maintain membrane integrity. In turn, the growth of ESCRT mutants strongly depended on TORC2-mediated homeostatic regulation of sphingolipid (SL) metabolism. This was caused by calcineurin-dependent dephosphorylation of Orm2, a repressor of SL biosynthesis. Calcineurin activity impaired Orm2 export from the endoplasmic reticulum (ER) and thereby hampered its subsequent endosome and Golgi-associated degradation (EGAD). The ensuing accumulation of Orm2 at the ER in ESCRT mutants necessitated TORC2 signaling through its downstream kinase Ypk1, which repressed Orm2 and prevented a detrimental imbalance of SL metabolism. Our findings reveal compensatory cross-talk between the ESCRT machinery, calcineurin/TORC2 signaling, and the EGAD pathway important for the regulation of SL biosynthesis and the maintenance of PM homeostasis.

The plant dehydrin Lti30 stabilizes lipid lamellar structures in varying hydration conditions

A major challenge to plant growth and survival are changes in temperature and diminishing water supply. During acute temperature and water stress, plants often express stress proteins, such as dehydrins, which are intrinsically disordered hydrophilic proteins. In this article, we investigated how the dehydrin Lti30 from Arabidopsis thaliana stabilizes membrane systems that are exposed to large changes in hydration. We also compared the effects of Lti30 on membranes with those of the simple osmolytes urea and trimethylamine N-oxide. Using X-ray diffraction and solid-state NMR, we studied lipid-protein self-assembly at varying hydration levels. We made the following observations: 1) the association of Lti30 with anionic membranes relies on electrostatic attraction, and the protein is located in the bilayer interfacial membrane region; 2) Lti30 can stabilize the lamellar multilayer structure, making it insensitive to variations in water content; 3) in lipid systems with a composition similar to those present in some seeds and plants, dehydrin can prevent the formation of nonlamellar phases upon drying, which may be crucial for maintaining membrane integrity; and 4) Lti30 stabilizes bilayer structures both at high and low water contents, whereas the small osmolyte molecules mainly prevent dehydration-induced transitions. These results corroborate the idea that dehydrins are part of a sensitive and multifaceted regulatory mechanism that protects plant cells against stress.

Effects of steam pretreatment on fouled membrane in chemical cleaning for flux recovery in drinking water treatment.

This paper shows the possibility of using steam pretreatment to improve the efficiency of membrane recovery chemical cleaning. Before applying chemicals to clean a fouled membrane, steam pretreatment was employed to loosen the structure of the foulant layer and weaken the attachment of those foulants on the membrane. Although longer steam contact times would lead to even better cleaning efficiency, the steam pretreatment duration was limited to less than 2min to maintain membrane integrity. When cleaning fouled membranes with 1mol/L HCl, the cleaning efficiency without steam pretreatment went from 83.3 to 90.2% as cleaning time increased from 30 to 180min. As for 90-s steam pretreatment, the cleaning efficiency showed high values of more than 93% regardless of cleaning time. When the concentration of HCl was decreased to 0.2mol/L, the cleaning efficiencies with a 90-s steam pretreatment was 78.6% and 92.6% for relatively short cleaning times of 30 and 60min, respectively; this is much higher than the 62.2% and 76.7% achieved when cleaning without steam pretreatment. In addition, when using alkaline solution as the cleaning chemical, similar results were obtained. This implies that the application of steam before chemical cleaning is effective in improving cleaning efficiency, and so, this technique has the potential to reduce the amount of cleaning chemical required for membrane recovery cleaning.

Membrane‐Associated Nucleobase‐Functionalized β‐Peptides (β‐PNAs) Affecting Membrane Support and Lipid Composition

Protein‐membrane interactions are essential to maintain membrane integrity and control membrane morphology and composition. Cytoskeletal proteins in particular are known to interact to a high degree with lipid bilayers and to line the cytoplasmic side of the plasma membrane with an extensive network structure. In order to gain a better mechanistical understanding of the protein–membrane interplay and possible membrane signaling, we started to develop a model system based on β‐peptide nucleic acids (β‐PNAs). These β‐peptides are known to form stable hydrogen‐bonded aggregates due to their helical secondary structure, which serve to pre‐organize the attached nucleobases. After optimization of the β‐PNA solid‐phase peptide synthesis and validation of helix formation, the ability of the novel β‐PNAs to dimerize and interact with lipid bilayers was investigated by both fluorescence and circular dichroism spectroscopy. It was shown that duplex formation occurs rapidly and with high specificity and could also be detected on the surfaces of the lipid bilayers. Hereby, the potential of a β‐PNA‐based peptide system to mimic membrane‐associated protein networks could be demonstrated.

Isolation, characterization and cytoprotective effects against UV radiation of exopolysaccharide produced from Paenibacillus polymyxa PYQ1

A novel exopolysaccharide (EPS) from Paenibacillus polymyxa PYQ1 was extracted, well purified and characterized. This EPS was homogeneous glucomannan-type polysaccharide with the average molecular weight of 4.38× 106Da. Structural characterization indicated that the monosaccharides of EPS were pyranoses connected by β-glycosidic linkages. Furthermore, our results showed the protective benefits of EPS against UVC induced cytotoxicity in HaCaT cells through scavenging excessive reactive oxygen species, mitigating the decrease of mitochondrial membrane potential, improving catalase activity and maintaining membrane integrity. Taken together, this study qualified EPS from P.polymyxa PYQ1 was a promising natural polymer which worth further investigation as a skin-care agent.