In vivo study of the state of order of the membranes of gram-negative bacteria by Fourier-transform infrared spectroscopy (FT-IR)

Carotenogenesis of Staphylococcus aureus: New insights and impact on membrane biophysical properties

Staphyloxanthin (STX) is a saccharolipid derived from a carotenoid in Staphylococcus aureus involved in oxidative-stress tolerance and antimicrobial peptide resistance. STX influences the biophysical properties of the bacterial membrane and has been associated to the formation of lipid domains in the regulation of methicillin-resistance. In this work, a targeted metabolomics and biophysical characterization study was carried out to investigate the biosynthetic pathways of carotenoids, and their impact on the membrane biophysical properties. Five different S. aureus strains were investigated, including three wild-type strains containing the crtM gene related to STX biosynthesis, a crtM-deletion mutant, and a crtMN plasmid-complemented variant. LC-DAD-MS/MS analysis of extracts allowed the identification of 34 metabolites related to carotenogenesis in S. aureus at different growth phases (8, 24 and 48 h), showing the progression of these metabolites as the bacteria advances into the stationary phase. For the first time, 22 members of a large family of carotenoids were identified, including STX and STX-homologues, as well as Dehydro-STX and Dehydro-STX-homologues. Moreover, thermotropic behavior of the CH2 stretch of lipid acyl chains in live cells by FTIR, show that the presence of STX increases acyl chain order at the bacterial growth temperature. Indeed, the cooperative melting event of the bacterial membrane, which occurs around 15 °C in the native strains, shifts with increased carotenoid content. These results show the diversity biosynthetic of carotenoids in S. aureus, and their influence on membrane biophysical properties.

Discrimination of heavy metal acclimated environmental strains by chemometric analysis of FTIR spectra

Heavy metal acclimated bacteria are profoundly the preferred choice for bioremediation studies. Bacteria get acclimated to toxic concentrations of heavy metals by induction of specific enzymes and genetic selection favoring new metabolic abilities leading to activation of one or several of resistance mechanisms creating bacterial populations with differences in resistance profile and/or level. Therefore, to use in bioremediation processes, it is important to discriminate acclimated bacterial populations and choose a more resistant strain. In this study, we discriminated heavy metal acclimated bacteria by using Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy and multivariate analysis methods namely Hierarchical Cluster Analysis (HCA), Principal Component Analysis (PCA) and Soft Independent Modeling of Class Analogy (SIMCA). Two acclimation methods, acute and gradual, were used which cause differences in molecular changes resulting in bacterial populations with different molecular and resistance profiles. Brevundimonas sp., Gordonia sp., and Microbacterium oxydans were exposed to the toxic concentrations of Cd (30 μg/ml) or Pb (90 μg/ml) by using broth medium as a growth media. Our results revealed that PCA and HCA clearly discriminated the acute-acclimated, gradual-acclimated, and control bacteria from each other in protein, carbohydrate, and whole spectral regions. Furthermore, we classified acclimated (acute and gradual) and control bacteria more accurately by using SIMCA with 99.9% confidence. This study demonstrated that heavy metal acclimated and control group bacteria can be discriminated by using chemometric analysis of FTIR spectra in a powerful, cost-effective, and handy way. In addition to the determination of the most appropriate acclimation procedure, this approach can be used in the detection of the most resistant bacterial strains to be used in bioremediation studies.

FTIR spectroscopy offers hints towards widespread molecular changes in cobalt-acclimated freshwater bacteria

High concentrations of heavy metals can be toxic for bacteria. However, after prolonged exposure, bacteria can become acclimated and begin to be able to grow in the presence of heavy metals. Acclimation can involve alterations of metabolism and molecular structures. Our aim was to examine these alterations in cobalt-acclimated bacteria via attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy on viable samples. Bacillus sp. and Pseudomonas sp. isolated from a temperate shallow lake and a well-established strain of E. coli were investigated. Our results revealed consistent, wide-spread changes in cell membrane and cell wall dynamics of Bacillus sp. and E. coli, including a decrease in peptidoglycan content of Bacillus sp. and increased lipid ordering of the membrane in both bacteria. Furthermore, a decrease in RNA and protein concentrations of Bacillus sp. was measured. All three bacteria studied showed a decrease in conformational freedom of proteins following cobalt acclimation. Interestingly, both Bacillus sp. and E. coli showed slight but significant alterations in their DNA conformations which might imply a methylation-mediated memory formation leading to epigenetic modulation for cobalt adaptation.

Low dose simvastatin induces compositional, structural and dynamic changes in rat skeletal extensor digitorum longus muscle tissue

Statins are commonly used drugs in the treatment of hypercholesterolaemia. There are many adverse effects of statins on skeletal muscle, but the underlying mechanisms remain unclear. In the present study, the effects of low dose (20 mg/kg) simvastatin, a lipophilic statin, on rat EDL muscle (extensor digitorum longus muscle) were investigated at the molecular level using FTIR (Fourier-transform infrared) spectroscopy. FTIR spectroscopy allows us rapid and sensitive determination of functional groups belonging to proteins, lipids, carbohydrates and nucleic acids simultaneously. The results revealed that simvastatin treatment induces a significant decrease in lipid, nucleic acid, protein and glycogen content. A significant increase in the lipid/protein and nucleic acid/protein ratios was also obtained with simvastatin treatment. Furthermore, an increase in lipid order and membrane fluidity was detected. A decrease in the bandwidth of the amide I band and shifting of the position of this band to higher frequency values in treated muscle indicates structural changes in proteins. Detailed secondary structure analysis of the amide I band revealed a significant increase in antiparallel and aggregated beta-sheet, random coil structure and a significant decrease in beta-sheet structure, which indicates protein denaturation.

Water structure in vitro and within Saccharomyces cerevisiae yeast cells under conditions of heat shock

The OH stretch mode from water and organic hydroxyl groups have strong infrared absorption, the position of the band going to lower frequency with increased H-bonding. This band was used to study water in trehalose and glycerol solutions and in genetically modified yeast cells containing varying amounts of trehalose. Concentration-dependent changes in water structure induced by trehalose and glycerol in solution were detected, consistent with an increase of lower-energy H-bonds and interactions at the expense of higher-energy interactions. This result suggests that these molecules disrupt the water H-bond network in such a way as to strengthen molecule-water interactions while perturbing water-water interactions. The molecule-induced changes in the water H-bond network seen in solution do not translate to observable differences in yeast cells that are trehalose-deficient and trehalose-rich. Although comparison of yeast with low and high trehalose showed no observable effect on intracellular water structure, the structure of water in cells is different from that in bulk water. Cellular water exhibits a larger preference for lower-energy H-bonds or interactions over higher-energy interactions relative to that shown in bulk water. This effect is likely the result of the high concentration of biological molecules present in the cell. The ability of water to interact directly with polar groups on biological molecules may cause the preference seen for lower-energy interactions.

Differentiation of mesophilic and thermophilic bacteria with fourier transform infrared spectroscopy

In the present study the characterization and differentiation of mesophilic and thermophilic bacteria were investigated by using Fourier transform infrared (FT-IR) spectroscopy. Our results showed significant differences between the FT-IR spectra of mesophilic and thermophilic bacteria. The protein-to-lipid ratio was significantly higher for thermophiles compared to mesophiles. The absorption intensity of the CH(3) asymmetric stretching vibration was higher in thermophilic bacteria, indicating a change in the composition of the acyl chains. The higher intensity/area observed in the CH(2) symmetric stretching mode at 2857 cm(-1), and the CH(2) bending vibration band at 1452 cm(-1), indicated a higher amount of saturated lipids in thermophilic bacteria. The lipid C=O stretching vibration at 1739 cm(-1), which was observed in the mesophilic group, was not observed clearly in the thermophilic group, indicating a difference in packing that is presumably due to the decreased proportion of unsaturated acyl chains in thermophilic bacteria. In addition, the carbonyl groups become hydrogen bonded and the cellular DNA content was lower in thermophilic bacteria. Moreover, in the 1000-400 cm(-1) frequency region, the spectra of each bacterial species belonging to both the mesophilic and thermophilic bacterial groups, showed characteristic differences that were discriminated via dendrogram using cluster analysis. The current study implies that FT-IR spectroscopy could be successfully applied for the rapid comparison of bacterial groups and species to establish either similarities or discrepancies, as well as to confirm biochemical or physiological characteristics.

17Beta-estradiol induced compositional, structural and functional changes in rainbow trout liver, revealed by FT-IR spectroscopy: a comparative study with nonylphenol

Steroidal hormones produced by humans and animals are constantly being excreted into the environment. It has been demonstrated that sewage effluent discharged to surface water contains natural estrogens and synthetic estrogenic chemicals. As estrogen levels continuously increase in the aquatic environment, it is very important to have a detailed understanding of estrogens' effects on fish. In the present study, juvenile rainbow trout (Oncorhynchus mykiss) were exposed to 17beta-estradiol (E2) for 3 weeks and the effects of E2 on rainbow trout livers were investigated at the molecular level using Fourier transform infrared spectroscopy. The results revealed that E2 induced significant alterations in the liver tissues. A decrease in glycogen levels and protein concentration, and an increase in both the population of hepatic lipids, especially triglycerides, as well as the relative content of nucleic acids was observed in the E2 treated liver. In addition, a decrease in the membrane fluidity and an increase in lipid order were found in the cells of treated samples. In order to compare the effect of E2 with that of NP at molecular level, the fish were also treated with an estrogenic compound, nonylphenol (NP). The NP-treated fish liver spectra were found to be quite similar to those of E2-treated fish confirming that NP mimics the effect of E2 in immature rainbow trout.

Evidence for the mechanism of photocatalytic degradation of the bacterial wall membrane at the TiO2 interface by ATR-FTIR and laser kinetic spectroscopy

The photocatalytic peroxidation of E. coli cell, lipo-polysaccharide (LPS), phosphatidyl-ethanolcholine (PE), and peptidoglycan (PGN) of the E. coli membrane wall has been investigated on TiO2 porous films by ATR-FTIR spectroscopy. The fast reactions of the photogenerated charge carriers in TiO2 with E. coli, LPS, and PE were monitored by laser kinetic spectroscopy. ATR-FTIR spectroscopy allowed the identification of E. coli, LPS, PE, and PGN as photocatalytic peroxidation products. The PGN was observed to be the most resistant membrane wall component. Shorter peroxidation times were observed for LPS and PE. Laser photolysis shows that E. coli, LPS, and PE compete in the scavenging of a surface trapped holes (h+) with the recombination reaction of h+ with the generated electrons (e-) within times > 50 ns. This scavenging leads to the formation of organic radicals initiating the radical chain peroxidation of E. coli, LPS, PE, and PE.

Analysis of Microbial Components Using LC−IR

Characterization of bacteria is currently an important research area in the medical, military, food, and agricultural sciences. In recent years, FT-IR has found an application as a microbiological detection method and as a general research tool. When coupled with a liquid chromatographic system, a new facet of research has evolved. By utilizing the separation ability of typical liquid chromatography systems, matrix elimination is possible, therefore allowing for clean spectra of cellular components. Information about the compositional makeup of various bacteria enhances the overall understanding of biology at the cellular level, provides a quantification of the chemistry of cellular processes, and can be used as a general identification tool. Both whole cells and lysed Escherichia coli cells were investigated in the present study. The cellular components consisting of proteins, glycoproteins, phospholipids, fatty amides and acids, and genomic materials were separated, isolated, and identified by FT-IR.

Bacterial swarming: a biochemical time-resolved FTIR-ATR study of Proteus mirabilis swarm-cell differentiation

Fourier transform infrared spectroscopy was applied to the study of the differentiation process undergone by Proteus mirabilis. This bacterium exhibits a remarkable dimorphism, allowing the cells to migrate on a solid substratum in a concerted manner yielding characteristic ring patterns. We performed an in situ noninvasive analysis of biochemical events occurring as vegetative cells differentiate into elongated, multinucleate, nonseptate, and hyperflagellated swarm cells. The major findings arising from this study are (i) the real-time monitoring of flagellar filament assembly, (ii) the evidence for de novo synthesis of qualitatively different lipopolysaccharides (LPS) and/or exopolysaccharides (EPS) constituting the slime into which bacteria swarm, and (iii) the alteration in the membrane fatty acid composition with a concomitant 10 degrees C decrease in the gel/liquid crystal phase transition resulting in an elevated membrane fluidity in swarm cells at the growth temperature. The time course of events shows that the EPS-LPS syntheses are synchronous with membrane fatty acid alterations and occur about 1 h before massive flagellar filament assembly is detected. This study not only provided a time sketch of biochemical events involved in the differentiation process but also led to the identification of the major spectral markers of both vegetative and swarm cells. This identification will allow to resolve the time-space structure of P. mirabilis colonies by using infrared microscopy.

Fourier-transform infrared spectroscopy: a pharmacotoxicologic tool for in vivo monitoring radical aggression

Among the physico-chemical methods that can be used to investigate induced peroxidation in living cells, Fourier transform infrared (FT-IR) spectroscopy appears to be a valuable technique as it is non-destructive and sensitive for monitoring changes in the vibrational spectra of samples. We examined microsomal fractions from rat liver and brain by FT-IR to study the effect of radical aggression induced in vivo by carbon tetrachloride (CCl4). The length of the acyl chains was increased as a consequence of peroxidation induced by the xenobiotic. Moreover, an enhanced level of cholesterol esters and an increase in phospholipids were observed in the liver and the brain, respectively. The conformational structure of the membrane proteins was changed in both the liver and the brain. In the polysaccharide region, we observed an important loss in glucidic structures, such as a decrease in liver glycogen and in some brain glycolipids. These alterations are probably due to the interactions between cells and CCl4and the metabolic changes caused by CCl4. Thus, FT-IR spectroscopy appears to be an useful tool and an accurate means for rapidly investigating the in vivo biochemical alterations induced by CCl4in microsomes, and for correlating them with biochemical and physiological data.Key words: brain, carbon tetrachloride, FT-IR, liver, microsomes.

Pharmacologic application of fourier transform IR spectroscopy: in vivo toxicity of carbon tetrachloride on rat liver

Microsomal fractions from rat liver were examined by means of Fourier transform IR (FTIR) spectroscopy to study the in vivo toxic effect of carbon tetrachloride administered by intraperitoneal injection. Lipid content was significantly enhanced in the liver of treated rats compared with untreated ones. The level of saturated fatty acids largely increased while that of unsaturated acids slightly decreased as a consequence of lipid peroxidation induced by the xenobiotic compound. The conformational structure of membrane proteins was changed, which was shown by the large decrease in the alpha-helical configuration. In the polysaccharide region we observed an important loss in glucidic structures that could be related to the metabolic changes caused by carbon tetrachloride intoxication. Thus, FTIR spectroscopy appears to be a useful tool to rapidly investigate the chemical alterations induced by this drug in liver microsomes and to correlate them with biochemical and physiological data.

Detection of pathological molecular alterations in scrapie-infected hamster brain by Fourier transform infrared (FT-IR) spectroscopy

In this report a new approach for the identification of pathological changes in scrapie-infected Syrian hamster brains using Fourier transform infrared microspectroscopy is discussed. Using computer-based pattern recognition techniques and imaging, infrared maps with high structural contrast were obtained. This strategy permitted comparison of spectroscopic data from identical anatomical structures in scrapie-infected and control brains. Consistent alterations in membrane state-of-order, protein composition, carbohydrate and nucleic acid constituents were detected in scrapie-infected tissues. Cluster analysis performed on spectra of homogenized medulla oblongata and pons samples also reliably separated uninfected from infected specimens. This method provides a useful tool not only for the exploration of the disease process but also for the development of rapid diagnostic and screening techniques of transmissible spongiform encephalopathies.

Infrared studies of protein-induced perturbation of lipids in lipoproteins and membranes

The paper reviews the main recent publications concerning infrared (IR) spectroscopy as applied to the study of lipid-protein interactions in model and cell membranes, lipoproteins, and related systems (e.g. lung surfactant). The review focuses mainly on transmission IR. Based on the available data, a number of general conclusions are presented on the perturbations caused by proteins on either the hydrocarbon chains, the polar headgroups or the interface region. Lipid-protein interactions in native cell membranes do not reveal significant differences from what is observed in semisynthetic model systems.

Evidence for a new type of outer membrane lipid in oral spirochete Treponema denticola. Functioning permeation barrier without lipopolysaccharides

A new class of outer membrane lipid (OML) was isolated from the oral spirochete Treponema denticola strain ATCC 33521 using a phenol/chloroform/light petroleum procedure normally applied for lipopolysaccharide extraction. In addition to chemical analysis, Fourier transform infrared (FTIR) spectroscopy was applied to compare the biophysical properties of OML with lipopolysaccharides (LPS) and lipoteichoic acids (LTA). Isolated OML fractions represent 1.4% of the total dry cell weight, are about 4 kDa in size, and contain 6% amino sugars, 8% neutral sugars, 14% phosphate, 35% carbazol-positive compounds, and 11% fatty acids (containing iso- and anteiso-fatty acyl chains). Rare for outer membrane lipids, OML contains no significant amount of 3-deoxy-D-manno-octulosonic acids, heptoses, and beta-hydroxy fatty acids. The fatty acyl chain composition, being similar to that of the cytoplasmic membrane, is quite heterogeneous with anteiso-pentadecanoic acid (12%), palmitic acid (51%), and iso-palmitic acid (19%) as the predominant fatty acids present. Findings of a glycerol-hexose unit and two glycerol-hexadecanoic acid fragments indicate a glycolipid membrane anchor typically found in LTA. There was also no evidence for the presence of a sphingosine-based lipid structure. The results of FTIR measurements strongly suggest that the reconstituted lipid forms normal bilayer structures (vesicles) expressing a high membrane state of order with a distinct phase transition as typical for isolated LPS. However, in contrast to LPS, OML of T. denticola has a lower Tm near 22 degreesC and a lower cooperativity of the phase transition. The results suggest a different kind of permeation barrier that is built up by this particular OML of T. denticola, which is quite different from LPS normally essential for Gram-negative bacteria.

Fluctuations in IR spectral parameters detected in mixed acyl chain membranes of Acholeplasma laidlawii B

Acholeplasma laidlawii B cells were grown at 37 degrees C on three binary C16:0-d(31)/C18:1 fatty acid mixtures at initial mol ratios of 3:2, 1:1, and 2:3. These mol ratios produced final C16:0-d(31)/C18:1 lipid acyl chain mol ratios of 1.66 +/- 0.23 (n=6), 1.3 +/- 0.20 (n=6) and 0.58 +/- 0.09 (n=10), respectively, in the membrane of the microorganism. Membrane conformational order for the deuterated and proteated acyl chains in intact cells was monitored by FT-IR spectroscopy through the thermotropic response of the acyl chain CD2 and CH2 stretching frequencies. Intact cells and isolated membranes revealed broad phase transitions centered well below the growth temperature. This result differs from previous studies (Moore, D.J. and Mendelsohn, R. (1994) Biochemistry 33, 4080-4085) of cells grown on a single saturated fatty acid source, where Tm was close to the growth temperature. Fluctuations in IR spectral parameters from the liquid crystalline phases were detected in ten separate samples of cells grown on a 2:3 mixture (final mol ratio 0.58:1) of C16:0-d(31)/C18:1, and in no other cell preparation. These were manifest by reduced precision in the measurement of CH2 and CD2 stretching frequencies and are attributed to fluctuations in the membrane conformational order. In addition to conformational order fluctuations in intact cells, similar behavior was noted for the simple binary phosphatidylcholine (PC) mixture, DOPC/1-C16:0-d(31),2-C18:1 PC (2:1 molar ratio). In this instance, the fluctuations were also detected through the temporal and thermotropic response of the relative intensity of the 1341 cm(-1) band assigned to end-gauche conformers about the penultimate C-C bond in the oleoyl chains. The relationship of these observations to the Raman spectroscopic detection of packing fluctuations in highly unsaturated PC's (Litman, B.J., Lewis, N., and Levin, I.W. (1991) Biochemistry 30, 313-319) is considered.