Differences in membrane fluidity and fatty acid composition between phenotypic variants of Streptococcus pneumoniae

RNase R Affects the Level of Fatty Acid Biosynthesis Transcripts Leading to Changes in membrane Fluidity

Previous studies on RNase R have highlighted significant effects of this ribonuclease in several processes of Streptococcus pneumoniae biology. In this work we show that elimination of RNase R results in overexpression of most of genes encoding the components of type II fatty acid biosynthesis (FASII) cluster. We demonstrate that RNase R is implicated in the turnover of most of transcripts from this pathway, affecting the outcome of the whole FASII cluster, and ultimately leading to changes in the membrane fatty acid composition. Our results show that the membrane of the deleted strain contains higher proportion of unsaturated and long-chained fatty acids than the membrane of the wild type strain. These alterations render the RNase R mutant more prone to membrane lipid peroxidation and are likely the reason for the increased sensitivity of this strain to detergent lysis and to the action of the bacteriocin nisin. Reprogramming of membrane fluidity is an adaptative cell response crucial for bacterial survival in constantly changing environmental conditions. The data presented here is suggestive of a role for RNase R in the composition of S. pneumoniae membrane, with strong impact on pneumococci adaptation to different stress situations.

Effect of Goji Berry extract on cell viability of Lactiplantibacillus plantarum M5 microcapsules during in vitro gastrointestinal digestion

Lactiplantibacillus plantarum M5 and Goji Berry extract were co-microencapsulated to maintain the activity of cells during gastrointestinal digestion, and the mechanism by which they could maintain high activity was investigated. The results showed that the microcapsules with 3% Goji Berry extract(A-GE-3) had the largest encapsulation efficiency(EE) of 92.41 ± 0.58%. SEM showed that the structure of A-GE-3 microcapsules were smoother and denser. Cell viability in A-GE-3 microcapsules remained at 7.17 log10 CFU/g after gastrointestinal digestion. Meanwhile, during the gastrointestinal digestion with 3% Goji Berry extract, cell membrane damage detected by fluorescent probes propidium iodide(PI) and 1.1-N-phenylnaphthylamine(NPN) was significantly reduced; the contents of arginine, glutamic acid and oleic acid in cell membrane were increased, which helped to maintain the dynamic balance of intracellular pH and regulated cell membrane fluidity in response to gastrointestinal environment. This study demonstrated the potential of Goji Berry extract as a probiotic protector in gastrointestinal digestion.

A combination of proteomics, genetics, and physiology provides insights into the acid-tolerance phenotype of Pseudomonas pergaminensis F77

Acid tolerance is crucial for the effective and persistent mineral weathering by acid-producing bacteria. Here, the molecular basis of the acid tolerance of mineral-weathering Pseudomonas pergaminensis F77 was identified using proteomics analysis of the strain under acid stress. Then, the acid tolerance of strain F77 and its mutants with deletion of the acid tolerance-related genes orf03767, mcp, resR, nueR, yegD, and fxsA, which are involved in the two-component systems, DNA repair, nucleotide binding, and membrane parts, were compared. Finally, the acid tolerance-related physiological mechanisms of strain F77 and its mutants F77ΔnueR and F77ΔresR under acidic conditions were characterized. The significantly upregulated proteins in the acid-adapted and acid-challenged strain F77 included the proteins involved in metabolic pathways associated with ATPase, membrane components, organic acid transmembrane transporters, response to stimulus, nucleotide binding, ABC transporters, and two-component systems. The cell numbers decreased by 24-100% at pH ≤ 4.50, while the membrane fluidity increased by 22-61% at pH ≤ 5.50 for the mutants F77ΔnueR and F77ΔresR, compared with that of strain F77. The intracellular H+-ATPase activities decreased by 29-33% for the mutant F77ΔnueR at pH ≤ 4.50% and 33-79% for the mutant F77ΔresR at all tested pHs (pH ≤ 7.00); meanwhile, the ratios of intracellular NAD+/NADH decreased by 71-91% for the mutant F77ΔresR at all tested pHs (pH ≤ 7.00), compared with that of strain F77. Furthermore, the intracellular putrescine concentrations were reduced by 40-70% for the mutant F77ΔresR at all tested pHs (pH ≤ 7.00) compared with that of strain F77. Our findings suggested that multiple proteins and metabolic pathways were associated with bacterial acid tolerance and revealed that nueR and resR were involved in acid tolerance based on their modulation of multiple acid tolerance-related physiological functions in strain F77.

Different cellular fatty acid pattern and gene expression of planktonic and biofilm state Listeria monocytogenes under nutritional stress

Listeria monocytogenes is a Gram-positive bacterium frequently involved in food-borne disease outbreaks and is widely distributed in the food-processing environment. This work aims to depict the impact of nutrition deficiency on the survival strategy of L. monocytogenes both in planktonic and biofilm states. In the present study, cell characteristics (autoaggression, hydrophobicity and motility), membrane fatty acid composition of MRL300083 (Lm83) in the forms of planktonic and biofilm-associated cells cultured in TSB-YE and 10-fold dilutions of TSB-YE (DTSB-YE) were investigated. Additionally, the relative expression of related genes were also determined by RT-qPCR. It was observed that cell growth in different bacterial life modes under nutritional stress rendered the cells a distinct phenotype. The higher autoaggression (AAG) and motility of the planktonic cells in DTSB-YE is associated with better biofilm formation. An increased proportion of unsaturated fatty acid/saturated fatty acid (USFA/SFA) indicates more fluidic biophysical properties for cell membranes of L. monocytogenes in planktonic and biofilm cells in DTSB-YE. Biofilm cells produced a higher percentage of USFA and straight fatty acids than the corresponding planktonic cells. An appropriate degree of membrane fluidity is crucial for survival, and alteration of membrane lipids is an essential adaptive response. The adaptation of bacteria to stress is a multifactorial cellular process, the expression of flagella-related genes fliG, fliP, flgE and the two-component chemotactic system cheA/Y genes of planktonic cells in DTSB-YE significantly increased compared to that in TSB-YE (p < 0.05). This study provides new information on the role of the physiological adaptation and gene expression of L. monocytogenes for planktonic and biofilm growth under nutritional stress.

Precise control of liposome size using characteristic time depends on solvent type and membrane properties

Controlling the sizes of liposomes is critical in drug delivery systems because it directly influences their cellular uptake, transportation, and accumulation behavior. Although hydrodynamic focusing has frequently been employed when synthesizing nano-sized liposomes, little is known regarding how flow characteristics determine liposome formation. Here, various sizes of homogeneous liposomes (50-400 nm) were prepared according to flow rate ratios in two solvents, ethanol, and isopropyl alcohol (IPA). Relatively small liposomes formed in ethanol due to its low viscosity and high diffusivity, whereas larger, more poly-dispersed liposomes formed when using IPA as a solvent. This difference was investigated via numerical simulations using the characteristic time factor to predict the liposome size; this approach was also used to examine the flow characteristics inside the microfluidic channel. In case of the liposomes, the membrane rigidity also has a critical role in determining their size. The increased viscosity and packing density of the membrane by addition of cholesterol confirmed by fluorescence anisotropy and polarity lead to increase in liposome size (40-530 nm). However, the interposition of short-chain lipids de-aligned the bilayer membrane, leading to its degradation; this decreased the liposome size. Adding short-chain lipids linearly decreased the liposome size (130-230 nm), but at a shallower gradient than that of cholesterol. This analytical study expands the understanding of microfluidic environment in the liposome synthesis by offering design parameters and their relation to the size of liposomes.

Integrative omics identifies conserved and pathogen-specific responses of sepsis-causing bacteria

Even in the setting of optimal resuscitation in high-income countries severe sepsis and septic shock have a mortality of 20-40%, with antibiotic resistance dramatically increasing this mortality risk. To develop a reference dataset enabling the identification of common bacterial targets for therapeutic intervention, we applied a standardized genomic, transcriptomic, proteomic and metabolomic technological framework to multiple clinical isolates of four sepsis-causing pathogens: Escherichia coli, Klebsiella pneumoniae species complex, Staphylococcus aureus and Streptococcus pyogenes. Exposure to human serum generated a sepsis molecular signature containing global increases in fatty acid and lipid biosynthesis and metabolism, consistent with cell envelope remodelling and nutrient adaptation for osmoprotection. In addition, acquisition of cholesterol was identified across the bacterial species. This detailed reference dataset has been established as an open resource to support discovery and translational research.

Bactericidal Activity of Carvacrol against Streptococcus pyogenes Involves Alteration of Membrane Fluidity and Integrity through Interaction with Membrane Phospholipids

Background: Carvacrol, a mono-terpenoid phenol found in herbs, such as oregano and thyme, has excellent antibacterial properties against Streptococcus pyogenes. However, its mechanism of bactericidal activity on S. pyogenes has not been elucidated. Objectives: This study investigated the bactericidal mechanism of carvacrol using three strains of S. pyogenes. Methods: Flow cytometry (FCM) experiments were conducted to determine carvacrol’s membrane permeabilization and cytoplasmic membrane depolarization activities. Protoplasts of S. pyogenes were used to investigate carvacrol’s effects on the membrane, followed by gel electrophoresis. The carvacrol-treated protoplasts were examined by transmission electron microscopy (TEM) to observe ultrastructural morphological changes. The fluidity of the cell membrane was measured by steady-state fluorescence anisotropy. Thin-layer chromatographic (TLC) profiling was conducted to study the affinity of carvacrol for membrane phospholipids. Results: Increased membrane permeability and decreased membrane potential from FCM and electron microscopy observations revealed that carvacrol killed the bacteria primarily by disrupting membrane integrity, leading to whole-cell lysis. Ultra-structural morphological changes in the membrane induced by carvacrol over a short period were confirmed using the S. pyogenes protoplast and membrane isolate models in vitro. In addition, changes in the other biophysical properties of the bacterial membrane, including concentration- and time-dependent increased fluidity, were observed. TLC experiments showed that carvacrol preferentially interacts with membrane phosphatidylglycerol (P.G.), phosphatidylethanolamine (P.E.), and cardiolipins (CL). Conclusions: Carvacrol exhibited rapid bactericidal action against S. pyogenes by disrupting the bacterial membrane and increasing permeability, possibly due to affinity with specific membrane phospholipids, such as P.E., P.G., and CL. Therefore, the bactericidal concentration of carvacrol (250 µg/mL) could be used to develop safe and efficacious natural health products for managing streptococcal pharyngitis or therapeutic applications.

Lipid-mediated antimicrobial resistance: a phantom menace or a new hope?

The proposition of a post-antimicrobial era is all the more realistic with the continued rise of antimicrobial resistance. The development of new antimicrobials is failing to counter the ever-increasing rates of bacterial antimicrobial resistance. This necessitates novel antimicrobials and drug targets. The bacterial cell membrane is an essential and highly conserved cellular component in bacteria and acts as the primary barrier for entry of antimicrobials into the cell. Although previously under-exploited as an antimicrobial target, the bacterial cell membrane is attractive for the development of novel antimicrobials due to its importance in pathogen viability. Bacterial cell membranes are diverse assemblies of macromolecules built around a central lipid bilayer core. This lipid bilayer governs the overall membrane biophysical properties and function of its membrane-embedded proteins. This mini-review will outline the mechanisms by which the bacterial membrane causes and controls resistance, with a focus on alterations in the membrane lipid composition, chemical modification of constituent lipids, and the efflux of antimicrobials by membrane-embedded efflux systems. Thorough insight into the interplay between membrane-active antimicrobials and lipid-mediated resistance is needed to enable the rational development of new antimicrobials. In particular, the union of computational approaches and experimental techniques for the development of innovative and efficacious membrane-active antimicrobials is explored.

Reduction of mussel metamorphosis by inactivation of the bacterial thioesterase gene via alteration of the fatty acid composition

The molecular mechanism underlying modulation of metamorphosis of the bivalve Mytilus coruscus by bacteria remains unclear. Here, the functional role of the thioesterase gene tesA of the bacterium Pseudoalteromonas marina in larval metamorphosis was examined. The aim was to determine whether inactivation of the tesA gene altered the biofilm-inducing capacity, bacterial cell motility, biopolymers, or the intracellular c-di-GMP levels. Complete inactivation of tesA increased the c-di-GMP content in P. marina, accompanied by a reduced fatty acid content, weaker motility, upregulation of bacterial aggregation, and biofilm formation. The metamorphosis rate of mussel larvae on ΔtesA biofilms was reduced by ∼ 80% compared with those settling on wild-type P. marina. Exogenous addition of a mixture of extracted fatty acids from P. marina into the ΔtesA biofilms promoted the biofilm-inducing capacity. This study suggests that the bacterial thioesterase gene tesA altered the fatty acid composition of ΔtesA P. marina biofilms (BF) through regulation of its c-di-GMP, subsequently impacting mussel metamorphosis.

Inactivation of Transcriptional Regulator FabT Influences Colony Phase Variation of Streptococcus pneumoniae

Streptococcus pneumoniae is an opportunistic pathogen that can alter its cell surface phenotype in response to the host environment. We demonstrated that the transcriptional regulator FabT is an indirect regulator of capsular polysaccharide, an important virulence factor of Streptococcus pneumoniae. Transcriptome analysis between the wild-type D39s and D39ΔfabT mutant strains unexpectedly identified a differentially expressed gene encoding a site-specific recombinase, PsrA. PsrA catalyzes the inversion of 3 homologous hsdS genes in a type I restriction-modification (RM) system SpnD39III locus and is responsible for the reversible switch of phase variation. Our study demonstrated that upregulation of PsrA in a D39ΔfabT mutant correlated with an increased ratio of transparent (T) phase variants. Inactivation of the invertase PsrA led to uniform opaque (O) variants. Direct quantification of allelic variants of hsdS derivatives and inversions of inverted repeats indicated that the recombinase PsrA fully catalyzes the inversion mediated by IR1 and IR3, and FabT mediated the recombination of the hsdS alleles in PsrA-dependent and PsrA-independent manners. In addition, compared to D39s, the ΔfabT mutant exhibited reduced nasopharyngeal colonization and was more resistant to phagocytosis and less adhesive to epithelial cells. These results indicated that phase variation in the ΔfabT mutant also affects other cell surface components involved in host interactions.

Temperature and presence of ethanol affect accumulation of intracellular trehalose in Lactobacillus plantarum WCFS1 upon pulsed electric field treatment

Pulsed electric field (PEF) treatment can be used to increase intracellular small molecule concentrations in bacteria, which can lead to enhanced robustness of these cells during further processing. In this study we investigated the effects of the PEF treatment temperature and the presence of 8% (v/v) ethanol in the PEF medium on cell survival, membrane fluidity and intracellular trehalose concentrations of Lactobacillus plantarum WCFS1. A moderate PEF treatment temperature of 21 °C resulted in a high cell survival combined with higher intracellular trehalose concentrations compared to a treatment at 10 and 35 °C. Interestingly, highest intracellular trehalose concentrations were observed upon supplementing the PEF medium with 8% ethanol, which resulted in more than a doubling in intracellular trehalose concentrations, while culture survival was retained. Overall, this study shows that treatment temperature and PEF medium optimization are important directions for improving molecule uptake upon PEF processing.

Lipophilic Arginine Esters: The Gateway to Preservatives without Side Effects

This study hypothesized that long carbon chain cationic arginine (Arg) esters can be considered as toxicologically harmless preservatives. Arg-esters with C₁₈ and C₂₄ carbon chains, namely, arginine-oleate (Arg-OL) and arginine-decyltetradecanoate (Arg-DT), were synthesized. Structures were confirmed by FT-IR, ¹H NMR, and mass spectroscopy. Both Arg-esters were tested regarding hydrophobicity in terms of log P_{octanol/water}, critical micelle concentration (CMC), biodegradability, cytotoxicity, hemolysis, and antimicrobial activity against Escherichiacoli (E. coli), Staphylococcusaureus (S. aureus), Bacillussubtilis (B. subtilis), and Enterococcusfaecalis (E. faecalis). Log P_{octanol/water} of arginine was raised from −1.9 to 0.3 and 0.6 due to the attachment of C₁₈ and C₂₄ carbon chains, respectively. The critical micelle concentration of Arg-OL and Arg-DT was 0.52 and 0.013 mM, respectively. Both Arg-esters were biodegradable by porcine pancreatic lipase. In comparison to the well-established antimicrobials, benzalkonium chloride (BAC) and cetrimide, Arg-esters showed significantly less cytotoxic and hemolytic activity. Both esters exhibited pronounced antimicrobial properties against Gram-positive and Gram-negative bacteria comparable to that of BAC and cetrimide. The minimum inhibitory concentration (MIC) of Arg-esters was <50 μg mL^–1 against all tested microbes. Overall, results showed a high potential of Arg-esters with long carbon chains as toxicologically harmless novel preservatives.

Isolate Specific Cold Response of Yersinia enterocolitica in Transcriptional, Proteomic, and Membrane Physiological Changes

Yersinia enterocolitica, a zoonotic foodborne pathogen, is able to withstand low temperatures. This psychrotrophic ability allows it to multiply in food stored in refrigerators. However, little is known about the Y. enterocolitica cold response. In this study, isolate-specific behavior at 4°C was demonstrated and the cold response was investigated by examining changes in phenotype, gene expression, and the proteome. Altered expression of cold-responsive genes showed that the ability to survive at low temperature depends on the capacity to acclimate and adapt to cold stress. This cold acclimation at the transcriptional level involves the transient induction and effective repression of cold-shock protein (Csp) genes. Moreover, the resumption of expression of genes encoding other non-Csp is essential during prolonged adaptation. Based on proteomic analyses, the predominant functional categories of cold-responsive proteins are associated with protein synthesis, cell membrane structure, and cell motility. In addition, changes in membrane fluidity and motility were shown to be important in the cold response of Y. enterocolitica. Isolate-specific differences in the transcription of membrane fluidity- and motility-related genes provided evidence to classify strains within a spectrum of cold response. The combination of different approaches has permitted the systematic description of the Y. enterocolitica cold response and gives a better understanding of the physiological processes underlying this phenomenon.

Investigation of the conserved reentrant membrane helix in the monotopic phosphoglycosyl transferase superfamily supports key molecular interactions with polyprenol phosphate substrates

Long-chain polyprenol phosphates feature in membrane-associated glycoconjugate biosynthesis pathways across domains of life. These unique amphiphilic molecules are best known as substrates of polytopic membrane proteins, including polyprenol-phosphate phosphoglycosyl and glycosyl transferases, and as components of more complex substrates. The linear polyprenols are constrained by double bond geometry and lend themselves well to interactions with polytopic membrane proteins, in which multiple transmembrane helices form a rich landscape for interactions. Recently, a new superfamily of monotopic phosphoglycosyl transferase enzymes has been identified that interacts with polyprenol phosphate substrates via a single reentrant membrane helix. Intriguingly, despite the dramatic differences in their membrane-interaction domains, both polytopic and monotopic enzymes similarly favor a unique cis/trans geometry in their polyprenol phosphate substrates. Herein, we present a multipronged biochemical and biophysical study of PglC, a monotopic phosphoglycosyl transferase that catalyzes the first membrane-committed step in N-linked glycoprotein biosynthesis in Campylobacter jejuni. We probe the significance of polyprenol phosphate geometry both in mediating substrate binding to PglC and in modulating the local membrane environment. Geometry is found to be important for binding to PglC; a conserved proline residue in the reentrant membrane helix is determined to drive polyprenol phosphate recognition and specificity. Pyrene fluorescence studies show that polyprenol phosphates at physiologically-relevant levels increase the disorder of the local lipid bilayer; however, this effect is confined to polyprenol phosphates with specific isoprene geometries. The molecular insights from this study may shed new light on the interactions of polyprenol phosphates with diverse membrane-associated proteins in glycoconjugate biosynthesis.

Metabolic adaptability shifts of cell membrane fatty acids of Komagataeibacter hansenii HDM1-3 improve acid stress resistance and survival in acidic environments

Komagataeibacter hansenii HDM1-3 (K. hansenii HDM1-3) has been widely applied for producing bacterial cellulose (BC). The yield of BC has been frequently limited by the acidification during sugar metabolism, due to the generation of organic acids such as acetic acid. In this study, the acid resistance mechanism of K. hansenii HDM1-3 has been investigated from the aspect of metabolic adaptability of cell membrane fatty acids. Firstly, we observed that the survival rate of K. hansenii HDM1-3 was decreased with lowered pH values (adjusted with acetic acids), accompanied by increased leakage rate. Secondly, the cell membrane adaptability in response to acid stress was evaluated, including the variations of cell membrane fluidity and fatty acid composition. The proportion of unsaturated fatty acids was increased (especially, C18-1w9c and C19-Cyc), unsaturation degree and chain length of fatty acids were also increased. Thirdly, the potential molecular regulation mechanism was further elucidated. Under acid stress, the fatty acid synthesis pathway was involved in the structure and composition variations of fatty acids, which was proved by the activation of both fatty acid dehydrogenase (des) and cyclopropane fatty acid synthase (cfa) genes, as well as the addition of exogenous fatty acids. The fatty acid synthesis of K. hansenii HDM1-3 may be mediated by the activation of two-component sensor signaling pathways in response to the acid stress. The acid resistance mechanism of K. hansenii HDM1-3 adds to our knowledge of the acid stress adaptation, which may facilitate the development of new strategies for improving the industrial performance of this species under acid stress.

Phase Variation of Streptococcus pneumoniae

Streptococcus pneumoniae undergoes phase variation or spontaneous, reversible phenotypic variation in colony opacity, encapsulation, and pilus expression. The variation in colony opacity appears to occur in all strains, whereas the switches in the production of the capsule and pilus have been observed in several strains. This chapter elaborates on the variation in colony opacity since this phenomenon has been extensively characterized. S. pneumoniae produces opaque and transparent colonies on the translucent agar medium. The different colony phases are fundamentally distinct phenotypes in their metabolism and multiple characteristics, as exemplified by cell surface features and phenotypes in colonization and virulence. Opaque variants, which express more capsular polysaccharides and fewer teichoic acids, are more virulent in animal models of sepsis but colonize the nasopharynx poorly. In contrast, transparent variants, with fewer capsular polysaccharides and more teichoic acid, colonize the nasopharynx in animal models more efficiently but are relatively avirulent. Lastly, pneumococcal opacity variants are generated by differential methylation of the genome DNA variation. The reversible switch in the methylation pattern is caused by DNA inversions in three homologous hsdS genes of the colony opacity determinant ( cod ) or SpnD39III locus, a conserved type I restriction-modification (RM) system. The hsdS gene encodes the sequence recognition subunit of the type I RM DNA methyltransferase. The combination of DNA inversion and differential methylation, a complex mechanism of phase variation, generates a mixed population that may allow for the selection of organisms in vivo with characteristics permissive for either carriage or systemic infection.

Adaptation of bacteria Escherichia coli in presence of quaternary ammonium ionic liquids

This paper presents the adaptation of Escherichia coli Gram-negative bacteria to increased concentrations of ionic liquids. Theophylline-based quaternary ammonium salts were used as an example of an ionic liquid that on the one hand includes an anion of natural origin and on the other hand is characterized by amphiphilic properties due to aliphatic chains in its structure. Theophylline-based ionic liquids can be synthesized relatively cheaply and easily and can exhibit strong antibacterial properties depending on the alkyl chain length. These compounds can also strongly affect bacterial membrane properties, including changes in electrokinetic potential as well as net surface charge. The experiments performed in this study succeeded in obtaining bacterial cultures growing at a tetradecyltrimethylammonium theophyllinate concentration three times higher than the minimum inhibition and bactericidal concentration. The adapted bacteria were characterized by intriguing changes in morphology and grew in the form of almost one-millimeter spheres in a liquid medium. It was shown that cultivation of adapted bacteria with tetradecyltrimethylammonium theophyllinate resulted in changes in the lipid membrane composition and protein patterns of the bacterial lysates, depending on the ionic liquid concentration. This study also revealed that such bacterial adaptation can increase sensitivity to antibiotics by affecting membrane properties like ionophores. These results can be potentially important with regard to synergistic or antagonistic action with other bactericidal compounds like antibiotics and nanoparticles.

Evaluation of membrane fluidity of multidrug-resistant isolates of Escherichia coli and Staphylococcus aureus in presence and absence of antibiotics

In the face of the serious problem of antimicrobial resistance and the global dissemination of multidrug-resistant (MDR) bacteria, it is relevant to deeply study such bacteria both genetically and phenotypically. It is well known that bacteria have the ability to modify the biophysical properties of their cytoplasmic membranes, namely fluidity, in order to survive and thrive in hostile environments. The aim of this study was to assess and compare the membrane fluidity among multidrug-resistant (MDR) isolates of Escherichia coli and Staphylococcus aureus in absence and in presence of antibiotics (ceftazidime or ciprofloxacin). The membrane fluidity was monitored at 24-h intervals up to three days and at the sixth day, by measuring the anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH) and the generalized polarization (GP) of Laurdan (6-dodecanoyl-2-dimethylaminonaphthalene). The anisotropy values as well as the Laurdan excitation GP (GP_exc) values obtained from all three E. coli strains (two MDR isolates and one susceptible reference strain) were quite similar and indicative of a very alike membrane phospholipid composition, regardless harboring or not resistance to multiple antimicrobials. Nonetheless, in the case of S. aureus, the anisotropy values were more increased in methicillin-resistant S. aureus (MRSA) isolates in comparison to the reference strain, meaning they have a less fluid membrane. Equally, GP_exc values were statistically different among the three S. aureus strains and showed that the two MRSA isolates had more rigid membranes than the susceptible strain. The exposition of MDR isolates of S. aureus to subinhibitory concentrations of ciprofloxacin did not affect neither the anisotropy values nor the GP_exc values, therefore, not altering membrane fluidity. Membrane integrity, assessed by the Live/Dead staining, of all strains and conditions studied was maintained over the six days. Thus, these preliminary studies on membrane properties of MDR isolates demonstrate that i) MRSA seem to have a more rigid membrane that susceptible S. aureus and ii) the presence of subinhibitory concentrations of antibiotics does not significantly alter the membrane fluidity of S. aureus, regardless being MDR or susceptible, but slightly affect the membrane fluidity of E. coli.

Membrane fluidity is involved in the regulation of heat stress induced secondary metabolism in Ganoderma lucidum

Ganoderma lucidum has become a potential model system for evaluating how environmental factors regulate the secondary metabolism of basidiomycetes. Heat stress (HS) is one of the most important environmental factors. It was previously reported that HS could induce the biosynthesis of ganoderic acids (GA). In this study, we found that HS increased GA biosynthesis and also significantly increased cell membrane fluidity. Furthermore, our results showed that addition of the membrane rigidifier dimethylsulfoxide (DMSO) could revert the increased GA biosynthesis elicited by HS. These results indicate that an increase in membrane fluidity is associated with HS-induced GA biosynthesis. Further evidence showed that the GA content was decreased in D9des-silenced strains and could be reverted to WT levels by addition of the membrane fluidizer benzyl alcohol (BA). In contrast, GA content was increased in D9des-overexpression strains and could be reverted to WT levels by the addition of DMSO. Furthermore, both membrane fluidity and GA biosynthesis induced by HS could be reverted by DMSO in WT and D9des-silenced strains. To the best of our knowledge, this is the first report demonstrating that membrane fluidity is involved in the regulation of heat stress induced secondary metabolism in filamentous fungi.

Effects of exposure to quaternary-ammonium-based biocides on antimicrobial susceptibility and tolerance to physical stresses in bacteria from organic foods

In the present study, a collection of 76 biocide-sensitive bacterial strains isolated from organically produced food were adapted by repeated exposure to increasing concentrations of the quaternary ammonium compounds (QACs) benzalkonium chloride (BC) and hexadecylpyridinium chloride (HDP). The sensitivity of both wildtype strains and their corresponding QAC-adapted strains to other biocides and to antibiotics was studied. QAC tolerance increased in 88.2% of strains for BC and in 30.3% of strains for HDP, with increases in minimum inhibitory concentrations between 2 and over 100 fold. Adaptive resistance was stable after 20 subcultures in biocide-free medium for 7 and 5 of the BC- and HDP-adapted strains, respectively. Adaptation to BC and HDP also reduced the susceptibility to other biocides, mainly hexachlorophene (CF), didecyldimethylammonium bromide (AB), triclosan (TC) and chlorhexidine (CH). BC-adapted strains showed increased antibiotic resistance to ampicillin (AM) followed by sulfamethoxazol (SXT) and cefotaxime (CTX), and some showed increased sensitivity to ceftazidime (CAZ), CTX, AM and STX. Changes in antibiotic resistance in HDP-adapted strains were more heterogeneous and strain-dependent. Main efflux pump genes detected in QAC-adapted strains were acrB, sugE, norC, qacE and qacH, as well as antibiotic resistance genes aac(6_)-Ie-aph(2_)-Ia, aph(2_)-Ic, ant(4_)-Ia, lsa, mrsA/B, ereA, ermB and cat. Membrane anisotropy experiments revealed that QAC adaptation induced an increase in membrane rigidity in the case of BC, while response to HDP was more heterogeneous and strain-dependent. Growth capacity was significantly higher in some QAC-adapted strains and strain-dependent changes in heat tolerance were also detected in QAC-adapted strains. Gastric acid or bile resistances do not seem to be influenced by QAC adaptation.

Involvement of NADH Oxidase in Biofilm Formation in Streptococcus sanguinis

Biofilms play important roles in microbial communities and are related to infectious diseases. Here, we report direct evidence that a bacterial nox gene encoding NADH oxidase is involved in biofilm formation. A dramatic reduction in biofilm formation was observed in a Streptococcus sanguinis nox mutant under anaerobic conditions without any decrease in growth. The membrane fluidity of the mutant bacterial cells was found to be decreased and the fatty acid composition altered, with increased palmitic acid and decreased stearic acid and vaccenic acid. Extracellular DNA of the mutant was reduced in abundance and bacterial competence was suppressed. Gene expression analysis in the mutant identified two genes with altered expression, gtfP and Idh, which were found to be related to biofilm formation through examination of their deletion mutants. NADH oxidase-related metabolic pathways were analyzed, further clarifying the function of this enzyme in biofilm formation.

Metabolism of Fructooligosaccharides in Lactobacillus plantarum ST-III via Differential Gene Transcription and Alteration of Cell Membrane Fluidity

Although fructooligosaccharides (FOS) can selectively stimulate the growth and activity of probiotics and beneficially modulate the balance of intestinal microbiota, knowledge of the molecular mechanism for FOS metabolism by probiotics is still limited. Here a combined transcriptomic and physiological approach was used to survey the global alterations that occurred during the logarithmic growth of Lactobacillus plantarum ST-III using FOS or glucose as the sole carbon source. A total of 363 genes were differentially transcribed; in particular, two gene clusters were induced by FOS. Gene inactivation revealed that both of the clusters participated in the metabolism of FOS, which were transported across the membrane by two phosphotransferase systems (PTSs) and were subsequently hydrolyzed by a β-fructofuranosidase (SacA) in the cytoplasm. Combining the measurements of the transcriptome- and membrane-related features, we discovered that the genes involved in the biosynthesis of fatty acids (FAs) were repressed in cells grown on FOS; as a result, the FA profiles were altered by shortening of the carbon chains, after which membrane fluidity increased in response to FOS transport and utilization. Furthermore, incremental production of acetate was observed in both the transcriptomic and the metabolic experiments. Our results provided new insights into gene transcription, the production of metabolites, and membrane alterations that could explain FOS metabolism in L. plantarum.

Advances in photocatalytic disinfection of bacteria: Development of photocatalysts and mechanisms

Photocatalysis has attracted worldwide attention due to its potential in solar energy conversion. As a "green" advanced oxidation technology, it has been extensively used for water disinfection and wastewater treatment. This article provides a review of the recent progress in solar energy-induced photocatalytic disinfection of bacteria, focusing on the development of highly efficient photocatalysts and their underlying mechanisms in bacterial inactivation. The photocatalysts are classified into TiO2-based and non-TiO2-based systems, as TiO2 is the most investigated photocatalyst. The synthesis methods, modification strategies, bacterial disinfection activities and mechanisms of different types of photocatalysts are reviewed in detail. Emphasis is given to the modified TiO2, including noble metal deposition, non-metal doping, dye sensitization and composite TiO2, along with typical non-TiO2-based photocatalysts for bacterial disinfection, including metal oxides, sulfides, bismuth metallates, graphene-based photocatalysts, carbon nitride-based photocatalysts and natural photocatalysts. A simple and versatile methodology by using a partition system combined with scavenging study is introduced to study the photocatalytic disinfection mechanisms in different photocatalytic systems. This review summarizes the current state of the work on photocatalytic disinfection of bacteria, and is expected to offer useful insights for the future development in the field.

Arachis hypogaea PGPR isolated from Argentine soil modifies its lipids components in response to temperature and salinity

The aim of this work was to clarify the mechanism related to plant growth promoting of a bacterial strain (L115) isolated from Arachis hypogaea rhizospheres and the effects of high growth temperature and salinity on phospholipids and fatty acids composition. L115 was isolated from peanut rhizospheres and identified according to the sequence analysis of the 16S rRNA gene. Phenotypic, metabolic and plant growth promoting rhizobacteria (PGPR) characteristics of L115 were tested. Inoculation test in plant growth chamber was performed. In addition, L115 was exposed to a 37 °C and 300 mM NaCl and phospholipids and fatty acid composition were evaluated. L115 strain was identified as Ochrobactrum intermedium and was able to increase the peanut shoot and root length as well as dry weight, indicating a PGPR role by being able to produce indole acetic acid and siderophores and present ACC deaminase activity. In addition, L115 showed tolerance to both high growth temperature and 300 mM NaCl. The most striking change was a decreased percentage of 18:1 fatty acid and an increase in 16:0 and 18:0 fatty acids, under high growth temperature or a combination of increased temperature and salinity. The most important change in phospholipid levels was an increase in phosphatidylcholine biosynthesis in all growth conditions. L115 can promote the growth of peanut and can tolerate high growth temperature and salinity modifying the fatty acid unsaturation degree and increasing phosphatidylcholine levels. This work is the first to report the importance of the genus Ochrobactrum as PGPR on peanut growth as well as on the metabolic behaviour against abiotic stresses that occur in soil. This knowledge will be useful for developing strategies to improve the growth of this bacterium under stress and to enhance its bioprocess for the production of inoculants.

The effects of lipids and surfactants on TLR5-proteoliposome functionality for flagellin detection using surface plasmon resonance biosensing

The use of proteoliposomes as affinity elements in conjunction with a surface plasmon resonance sensor is a high-sensitivity alternative for the detection of multiple analytes. However, one of the most important aspects of these conformations is maintaining the functionality of the immobilized protein, which is determined by the choice of lipids and surfactants employed in the reconstitutions. Previously, we demonstrated the functionality of TLR5-proteoliposomes as screening affinity elements of bacterial flagellin. In this new study we change the conditions of immobilization of TLR5 and evaluate how the fluidity of the membrane and the final size of the liposomes affect the functionality of the construct and thus increase their utility as an affinity element for design of new biosensors. In particular, we used reconstructions into preformed liposomes composed of the lipids POPC, POPC-DMPC and POPC-POPE mediated by the use of surfactants OG, Triton X100, and DDM, respectively. The affinity results were evaluated by SPR technology proteoliposomes and were correlated with the anisotropic change in the membrane status; the final sizes of the proteoliposomes were estimated. Our results clearly show the dependence of fluidity and final size of the proteoliposomes with surface plasmon resonance affinity measurements.

Modification of Fatty acids in membranes of bacteria: implication for an adaptive mechanism to the toxicity of carbon nanotubes

We explored whether bacteria could respond adaptively to the presence of carbon nanotubes (CNTs) by investigating the influence of CNTs on the viability, composition of fatty acids, and cytoplasmic membrane fluidity of bacteria in aqueous medium for 24 h exposure. The CNTs included long single-walled carbon nanotubes (L-SWCNTs), short single-walled carbon nanotubes (S-SWCNTs), short carboxyl single-walled carbon nanotubes (S-SWCNT-COOH), and aligned multiwalled carbon nanotubes (A-MWCNTs). The bacteria included three common model bacteria, Staphyloccocus aureus (Gram-positive), Bacillus subtilis (Gram-positive), and Escherichia coli (Gram-negative), and one polybrominated diphenyl ether degrading strain, Ochrobactrum sp. (Gram-negative). Generally, L-SWCNTs were the most toxic to bacteria, whereas S-SWCNT-COOH showed the mildest bacterial toxicity. Ochrobactrum sp. was more susceptible to the toxic effect of CNTs than E. coli. Compared to the control in the absence of CNTs, the viability of Ochrobactrum sp. decreased from 71.6-81.4% to 41.8-70.2%, and E. coli from 93.7-104.0% to 67.7-91.0% when CNT concentration increased from 10 to 50 mg L(-1). The cytoplasmic membrane fluidity of bacteria increased with CNT concentration, and a significant negative correlation existed between the bacterial viabilities and membrane fluidity for E. coli and Ochrobactrum sp. (p < 0.05), indicating that the increase in membrane fluidity induced by CNTs was an important factor causing the inactivation of bacteria. In the presence of CNTs, E. coli and Ochrobactrum sp. showed elevation in the level of saturated fatty acids accompanied with reduction in unsaturated fatty acids, compensating for the fluidizing effect of CNTs. This demonstrated that bacteria could modify their composition of fatty acids to adapt to the toxicity of CNTs. In contrast, S. aureus and B. subtilis exposed to CNTs increased the proportion of branched-chain fatty acids and decreased the level of straight-chain fatty acids, which was also favorable to counteract the toxic effect of CNTs. This study suggests that the bacterial tolerances to CNTs are associated with both the adaptive modification of fatty acids in the membrane and the physicochemical properties of CNTs. This is the first report about the physiologically adaptive response of bacteria to CNTs, and may help to further understand the ecotoxicological effects of CNTs.

Cellular membrane fluidity in amyloid precursor protein processing

The senile plaque is a pathologic hallmark of Alzheimer's disease (AD). Amyloid-β peptide (Aβ), the main constituent of senile plaques, is neurotoxic especially in its oligomeric form. Aβ is derived from the sequential cleavage of amyloid precursor protein (APP) by β- and γ-secretases in the amyloidogenic pathway. Alternatively, APP can be cleaved by α-secretases within the Aβ domain to produce neurotrophic and neuroprotective α-secretase-cleaved soluble APP (sAPPα) in the nonamyloidogenic pathway. Since APP and α-, β-, and γ-secretases are membrane proteins, APP processing should be highly dependent on the membrane composition and the biophysical properties of cellular membrane. In this review, we discuss the role of the biophysical properties of cellular membrane in APP processing, especially the effects of phospholipases A(2) (PLA(2)s), fatty acids, cholesterol, and Aβ on membrane fluidity in relation to their effects on APP processing.

Influence of nanoparticle-membrane electrostatic interactions on membrane fluidity and bending elasticity

The aim of this work is to investigate the effect of electrostatic interactions between the nanoparticles and the membrane lipids on altering the physical properties of the liposomal membrane such as fluidity and bending elasticity. For this purpose, we have used nanoparticles and lipids with different surface charges. Positively charged iron oxide (γ-Fe2O3) nanoparticles, neutral and negatively charged cobalt ferrite (CoFe2O4) nanoparticles were encapsulated in neutral lipid 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine and negatively charged 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-L-serine lipid mixture. Membrane fluidity was assessed through the anisotropy measurements using the fluorescent probe 1,6-diphenyl-1,3,5-hexatriene. Though the interaction of both the types of nanoparticles reduced the membrane fluidity, the results were more pronounced in the negatively charged liposomes encapsulated with positively charged iron oxide nanoparticles due to strong electrostatic attractions. X-ray photoelectron spectroscopy results also confirmed the presence of significant quantity of positively charged iron oxide nanoparticles in negatively charged liposomes. Through thermally induced shape fluctuation measurements of the giant liposomes, a considerable reduction in the bending elasticity modulus was observed for cobalt ferrite nanoparticles. The experimental results were supported by the simulation studies using modified Langevin-Poisson-Boltzmann model.

Interaction between dipolar lipid headgroups and charged nanoparticles mediated by water dipoles and ions

In this work, a theoretical model describing the interaction between a positively or negatively charged nanoparticle and neutral zwitterionic lipid bilayers is presented. It is shown that in the close vicinity of the positively charged nanoparticle, the zwitterionic lipid headgroups are less extended in the direction perpendicular to the membrane surface, while in the vicinity of the negatively charged nanoparticle, the headgroups are more extended. This result coincides with the calculated increase in the osmotic pressure between the zwitterionic lipid surface and positively charged nanoparticle and the decrease of osmotic pressure between the zwitterionic lipid surface and the negatively charged nanoparticle. Our theoretical predictions agree well with the experimentally determined fluidity of a lipid bilayer membrane in contact with positively or negatively charged nanoparticles. The prospective significance of the present work is mainly to contribute to better understanding of the interactions of charged nanoparticles with a zwitterionic lipid bilayer, which may be important in the efficient design of the lipid/nanoparticle nanostructures (like liposomes with encapsulated nanoparticles), which have diverse biomedical applications, including targeted therapy (drug delivery) and imaging of cancer cells.

Structural and functional characterisation of TesA - a novel lysophospholipase A from Pseudomonas aeruginosa

TesA from Pseudomonas aeruginosa belongs to the GDSL hydrolase family of serine esterases and lipases that possess a broad substrate- and regiospecificity. It shows high sequence homology to TAP, a multifunctional enzyme from Escherichia coli exhibiting thioesterase, lysophospholipase A, protease and arylesterase activities. Recently, we demonstrated high arylesterase activity for TesA, but only minor thioesterase and no protease activity. Here, we present a comparative analysis of TesA and TAP at the structural, biochemical and physiological levels. The crystal structure of TesA was determined at 1.9 Å and structural differences were identified, providing a possible explanation for the differences in substrate specificities. The comparison of TesA with other GDSL-hydrolase structures revealed that the flexibility of active-site loops significantly affects their substrate specificity. This assumption was tested using a rational approach: we have engineered the putative coenzyme A thioester binding site of E. coli TAP into TesA of P. aeruginosa by introducing mutations D17S and L162R. This TesA variant showed increased thioesterase activity comparable to that of TAP. TesA is the first lysophospholipase A described for the opportunistic human pathogen P. aeruginosa. The enzyme is localized in the periplasm and may exert important functions in the homeostasis of phospholipids or detoxification of lysophospholipids.

A pyrene- and phosphonate-containing fluorescent probe as guest molecule in a host polymer matrix

New host-guest materials have been prepared by incorporation of a home-made organic probe displaying a pyrene motif and a phosphonate function into a regular amphiphilic copolymer. Using powder X-Ray diffraction, photoluminescence and FT-IR spectroscopy, we have been able to study the non-covalent interactions between the host matrix and the guest molecule in the solid state. Interestingly, we have shown that the matrix directs the guest spatial localization and alters its properties. Thanks to the comparison of pyrene vs. N-pyrenylmaleimide derivatives, the influence of the chemical nature of the guest molecules on the non-covalent interactions with the host have been studied. In addition, using polyethylene glycol as a reference host, we have been able to evidence a true matrix effect within our new insertion materials. The phosphonated guest molecule appears to be a novel probe targeting the hydrophilic domain of the host copolymer.

Lactobacillus casei combats acid stress by maintaining cell membrane functionality

Lactobacillus casei strains have traditionally been recognized as probiotics and frequently used as adjunct culture in fermented dairy products where lactic acid stress is a frequently encountered environmental condition. We have investigated the effect of lactic acid stress on the cell membrane of L. casei Zhang [wild type (WT)] and its acid-resistant mutant Lbz-2. Both strains were grown under glucose-limiting conditions in chemostats; following challenge by low pH, the cell membrane stress responses were investigated. In response to acid stress, cell membrane fluidity decreased and its fatty acid composition changed to reduce the damage caused by lactic acid. Compared with the WT, the acid-resistant mutant exhibited numerous survival advantages, such as higher membrane fluidity, higher proportions of unsaturated fatty acids, and higher mean chain length. In addition, cell integrity analysis showed that the mutant maintained a more intact cellular structure and lower membrane permeability after environmental acidification. These results indicate that alteration in membrane fluidity, fatty acid distribution, and cell integrity are common mechanisms utilized by L. casei to withstand severe acidification and to reduce the deleterious effect of lactic acid on the cell membrane. This detailed comparison of cell membrane responses between the WT and mutant add to our knowledge of the acid stress adaptation and thus enable new strategies to be developed aimed at improving the industrial performance of this species under acid stress.

Phytosphingosine-1-phosphate is a signaling molecule involved in miconazole resistance in sessile Candida albicans cells

Previous research has shown that 1% to 10% of sessile Candida albicans cells survive treatment with high doses of miconazole (a fungicidal imidazole). In the present study, we investigated the involvement of sphingolipid biosynthetic intermediates in this survival. We observed that the LCB4 gene, coding for the enzyme that catalyzes the phosphorylation of dihydrosphingosine and phytosphingosine, is important in governing the miconazole resistance of sessile Saccharomyces cerevisiae and C. albicans cells. The addition of 10 nM phytosphingosine-1-phosphate (PHS-1-P) drastically reduced the intracellular miconazole concentration and significantly increased the miconazole resistance of a hypersusceptible C. albicans heterozygous LCB4/lcb4 mutant, indicating a protective effect of PHS-1-P against miconazole-induced cell death in sessile cells. At this concentration of PHS-1-P, we did not observe any effect on the fluidity of the cytoplasmic membrane. The protective effect of PHS-1-P was not observed when the efflux pumps were inhibited or when tested in a mutant without functional efflux systems. Also, the addition of PHS-1-P during miconazole treatment increased the expression levels of genes coding for efflux pumps, leading to the hypothesis that PHS-1-P acts as a signaling molecule and enhances the efflux of miconazole in sessile C. albicans cells.

Structural elucidation of diglycosyl diacylglycerol and monoglycosyl diacylglycerol from Streptococcus pneumoniae by multiple-stage linear ion-trap mass spectrometry with electrospray ionization

The cell wall of the pathogenic bacterium Streptococcus pneumoniae contains glucopyranosyl diacylglycerol (GlcDAG) and galactoglucopyranosyldiacylglycerol (GalGlcDAG). The specific GlcDAG consisting of vaccenic acid substituent at sn-2 was recently identified as another glycolipid antigen family recognized by invariant natural killer T-cells. Here, we describe a linear ion-trap multiple-stage (MS(n) ) mass spectrometric approach towards structural analysis of GalGlcDAG and GlcDAG. Structural information derived from MS(n) (n = 2, 3) on the [M + Li](+) adduct ions desorbed by electrospray ionization affords identification of the fatty acid substituents, assignment of the fatty acyl groups on the glycerol backbone, as well as the location of double bond along the fatty acyl chain. The identification of the fatty acyl groups and determination of their regio-specificity were confirmed by MS(n) (n = 2, 3) on the [M + NH(4) ](+) ions. We establish the structures of GalGlcDAG and GlcDAG isolated from S. pneumoniae, in which the major species consists of a 16:1- or 18:1-fatty acid substituent mainly at sn-2, and the double bond of the fatty acid is located at ω-7 (n-7). More than one isomers were found for each mass in the family. This mass spectrometric approach provides a simple method to achieve structure identification of this important lipid family that would be very difficult to define using the traditional method.

The Staphylococcus aureus two-component regulatory system, GraRS, senses and confers resistance to selected cationic antimicrobial peptides

The two-component regulatory system, GraRS, appears to be involved in staphylococcal responses to cationic antimicrobial peptides (CAPs). However, the mechanism(s) by which GraRS is induced, regulated, and modulated remain undefined. In this study, we used two well-characterized MRSA strains (Mu50 and COL) and their respective mutants of graR and vraG (encoding the ABC transporter-dependent efflux pump immediately downstream of graRS), and show that (i) the expression of two key determinants of net positive surface charge (mprF and dlt) is dependent on the cotranscription of both graR and vraG, (ii) reduced expression of mprF and dlt in graR mutants was phenotypically associated with reduced surface-positive charge, (iii) this net reduction in surface-positive charge in graR and vraG mutants, in turn, correlated with enhanced killing by a range of CAPs of diverse structure and origin, including those from mammalian platelets (tPMPs) and neutrophils (hNP-1) and from bacteria (polymyxin B), and (iv) the synthesis and translocation of membrane lysyl-phosphatidylglycerol (an mprF-dependent function) was substantially lower in graR and vraG mutants than in parental strains. Importantly, the inducibility of mprF and dlt transcription via the graRS-vraFG pathway was selective, with induction by sublethal exposure to the CAPs, RP-1 (platelets), and polymyxin B, but not by other cationic molecules (hNP-1, vancomycin, gentamicin, or calcium-daptomycin). Although graR regulates expression of vraG, the expression of graR was codependent on an intact downstream vraG locus. Collectively, these data support an important role of the graRS and vraFG loci in the sensing of and response to specific CAPs involved in innate host defenses.

Modification of the technical properties of Lactobacillus johnsonii NCC 533 by supplementing the growth medium with unsaturated fatty acids

The aim of this study was to investigate the influence of supplementing growth medium with unsaturated fatty acids on the technical properties of the probiotic strain Lactobacillus johnsonii NCC 533, such as heat and acid tolerance, and inhibition of Salmonella enterica serovar Typhimurium infection. Our results showed that the membrane composition and morphology of L. johnsonii NCC 533 were significantly changed by supplementing a minimal Lactobacillus medium with oleic, linoleic, and linolenic acids. The ratio of saturated to unsaturated plus cyclic fatty acids in the bacterial membrane decreased by almost 2-fold when minimal medium was supplemented with unsaturated fatty acids (10 μg/ml). The subsequent acid and heat tolerance of L. johnsonii decreased by 6- and 20-fold when the strain was grown in the presence of linoleic and linolenic acids, respectively, compared with growth in oleic acid (all at 10 μg/ml). Following acid exposure, significantly higher (P < 0.05) oleic acid content was detected in the membrane when growth medium was supplemented with linoleic or linolenic acid, indicating that saturation of the membrane fatty acids occurred during acid stress. Cell integrity was determined in real time during stressed conditions using a fluorescent viability kit in combination with flow cytometric analysis. Following heat shock (at 62.5°C for 5 min), L. johnsonii was unable to form colonies; however, 60% of the bacteria showed no cell integrity loss, which could indicate that the elevated heat inactivated vital processes within the cell, rendering it incapable of replication. Furthermore, L. johnsonii grown in fatty acid-enriched minimal medium had different adhesion properties and caused a 2-fold decrease in S. enterica serovar Typhimurium UK1-lux invasion of HT-29 epithelial cells compared with bacteria grown in minimal medium alone. This could be related to changes in the hydrophobicity and fluidity of the membrane. Our study shows that technical properties underlying probiotic survivability can be affected by nutrient composition of the growth medium.

Antioxidant micronutrient supplementation increases erythrocyte membrane fluidity in adults from a rural Chinese community

The objective of the present study was to investigate age-related differences in erythrocyte membrane fluidity (EMF) and changes in antioxidant capacity following supplementation. A total of seventy-four children were randomly divided into two groups: group A1 was the placebo-controlled group and group A2 was supplemented daily with 600 μg retinol, 1·0 mg β-carotene, 100 mg tocopherol, 300 mg ascorbic acid and 200 μg Se. A total of ninety young people were randomly divided into B1 and B2 groups, and ninety-one elderly subjects were divided into C1 and C2 groups. Groups B1 and C1 were placebo-controlled groups, and groups B2 and C2 were daily supplemented with 900 μg retinol, 1·5 mg β-carotene, 200 mg tocopherol, 500 mg ascorbic acid and 400 μg Se. Results showed that plasma malondialdehyde (MDA) was 5·35 μmol/l in children, which was lower than in young and elderly people. The MDA levels of the young and elderly individuals in the treated groups were significantly lower compared with the control groups, but the supplementation did not alter MDA levels in children. At baseline, there was a lower value of polarisation (ρ) and microviscosity (η) in children, indicating a higher EMF, than in both the young and elderly subjects. After the 2-month trial, the ρ and η values of young and elderly subjects in the treated groups decreased significantly in comparison with the placebo groups, indicating an increase in EMF. In conclusion, there was a background of higher MDA levels and lower EMF in young and elderly people than in children, which could be improved by antioxidant supplementation.