Freshwater biofilms play an essential ecological role, but they also adversely affect human activities through undesirable biofouling of artificial submerged structures. They form complex aggregates ...of microorganisms that colonize any type of substratum. In phototrophic biofilms, diatoms dominate in biomass and produce copious amount of extracellular polymeric substances (EPSs), making them efficient early colonizers. Therefore, a better understanding of diatoms adhesive properties is essential to develop new anti-biofouling strategies. In this context, we used atomic force microscopy (AFM) to decipher the topography and adhesive mechanisms of the common freshwater diatom Nitzschia palea. Images taken in physiological conditions revealed typical ultrastructural features with a few nanometers resolution. Using single-cell force spectroscopy, we showed that N. palea strongly adheres to hydrophobic surfaces as compared to hydrophilic ones. Chemical force spectroscopy with hydrophobic tips further confirmed that the adhesion is governed by surface-associated hydrophobic EPS distributed in clusters at the frustule surface, and mostly composed of (glyco)-lipids as revealed by Raman spectroscopy. Collectively, our results demonstrate that AFM-based nanoscopy, combined with Raman spectroscopy, is a powerful tool to provide new insights into the adhesion mechanisms of diatoms.
This study reports on the development of thermoresponsive core/shell magnetic nanoparticles (MNPs) based on an iron oxide core and a thermoresponsive copolymer shell composed of 2-(2-methoxy)ethyl ...methacrylate (MEO2MA) and oligo(ethylene glycol)methacrylate (OEGMA) moieties. These smart nano-objects combine the magnetic properties of the core and the drug carrier properties of the polymeric shell. Loading the anticancer drug doxorubicin (DOX) in the thermoresponsive MNPs via supramolecular interactions provides advanced features to the delivery of DOX with spatial and temporal controls. The so coated iron oxide MNPs exhibit superparamagnetic behavior with a saturation magnetization of around 30 emu g–1. Drug release experiments confirmed that only a small amount of DOX was released at room temperature, while almost 100% drug release was achieved after 52 h at 42 °C with Fe3−δO4@P(MEO2MA60OEGMA40), which grafted polymer chains displaying a low critical solution temperature of 41 °C. Moreover, the MNPs exhibit magnetic hyperthermia properties as shown by specific absorption rate measurements. Finally, the cytotoxicity of the core/shell MNPs toward human ovary cancer SKOV-3 cells was tested. The results showed that the polymer-capped MNPs exhibited almost no toxicity at concentrations up to 12 μg mL–1, whereas when loaded with DOX, an increase in cytotoxicity and a decrease of SKOV-3 cell viability were observed. From these results, we conclude that these smart superparamagnetic nanocarriers with stealth properties are able to deliver drugs to tumor and are promising for applications in multimodal cancer therapy.
In the field of actinide aqueous chemistry, this work aims to resolve some controversy about uranyl(VI) hydroxide species present in basic aqueous solutions. We revisit the Raman, IR, and UV−visible ...spectra with two new approaches. First, Raman, IR and UV data were recorded systematically from aqueous solutions with the noncomplexing electrolyte (C2H5)4NNO3 at 25 °C and 0.1 MPa (U total = 0.005−0.105 M) in H2O and D2O over a wide range of −log mH(D)+ between 2.92 and 14.50. Second, vibrational spectra (IR and Raman) of basic solutions in H2O and D2O were analyzed using the Bayesian Positive Source Separation method to estimate pure spectra of individual species. In D2O solutions, the new spectroscopic data showed the occurrence of the same species as those in H2O. As observed for the wavenumber of the symmetric stretching mode, the wavenumber characteristic of the OUO antisymmetric stretching mode decreases as the number of OH(D)− ligands increases. These kinds of data, completed by (1) analysis of the signal widths, (2) persistence of the apparent exclusion rule between IR and Raman spectra of the uranyl species stretching modes, and (3) interpretation of the absorption UV−visible spectra, allow discussion of the chemistry, structures, and polynuclearity of uranyl(VI) species. In moderate basic solutions, the presence of two trimers is suggested. In highly basic solutions (OH− ≈ 3 M), the two monomers UO2(OH)4 2− and UO2(OH)5 3− are confirmed to be in good agreement with earlier EXAFS and NMR results. The occurrence of the UO2(OH)6 4− monomer is also suggested from the more basic solutions investigated.
Bacteria grow on surfaces and form communities called biofilms. Bacterial adhesion and properties of the derived biofilms depend on, among others, the nature of the supporting substrate. Here, we ...report how the surface properties of the substrate affect the biofilm growth of probiotic Lactobacillus rhamnosus GG (LGG). Hydrophilic (OH), hydrophobic (CH3), and positively charged (NH3 +) surfaces were obtained by the functionalization of a ZnSe crystal with alkanethiol self-assembled monolayers (SAM). The self-assembly of alkanethiols onto ZnSe was studied in situ using infrared spectroscopy in attenuated total reflection mode (ATR-FTIR). The organization of grafted SAMs was analyzed based on the results of ATR-FTIR, high-energy elastic backscattering spectrometry, and contact angle measurements. The kinetics and adhesion strength of LGG initial attachment as well as its physiological state on surfaces terminated by the different functional groups were assessed by the combination of ATR-FTIR, force measurements based on atomic force microscopy, and fluorescent staining of bacteria. The strength of interactions between LGG and the surface was strongly affected by the terminal group of the alkanethiol chain. The −NH3 + groups displayed the highest affinity with LGG at the first stage of interaction. The surface properties also played an important role when LGG biofilms were further grown in a nutritive medium for 24 h under flow conditions. Notably, the analysis of the infrared spectra recorded during the biofilm cultivation revealed differences in the kinetics of growth and in the polysaccharide features of the biofilm depending on the substrate functionality. LGG biofilm was stable only on the positively charged surface upon rinsing. Findings of this work clearly show that the adhesion features and the growth of LGG biofilms are substrate-dependent.
Drinking water quality management requires early warning tools which enable water supply companies to detect quickly and to forecast degradation of the microbial quality of drinking water during its ...transport throughout distribution systems. This study evaluated the feasibility of assessing, in real time, drinking water biostability by monitoring in situ the evolution of the attenuated total reflectance-Fourier transform infrared (ATR-FTIR) fingerprint of a nascent reference biofilm exposed to water being tested. For this purpose, the responses of nascent Pseudomonas fluorescens biofilms to variations in the dissolved organic carbon (DOC) level in tap water were monitored in situ and in real time by ATR-FTIR spectroscopy. Nascent P. fluorescens biofilms consisting of a monolayer of bacteria were formed on the germanium crystal of an ATR flowthrough cell by pumping bacterial suspensions in Luria-Bertani (LB) medium through the cell. Then they were exposed to a continuous flow of dechlorinated sterile tap water supplemented with appropriate amounts of sterile LB medium to obtain DOC concentrations ranging from 1.5 to 11.8 mg/liter. The time evolution of infrared bands related to proteins, polysaccharides, and nucleic acids clearly showed that changes in the DOC concentration resulted in changes in the nascent biofilm ATR-FTIR fingerprint within 2 h after exposure of the biofilm to the water being tested. The initial bacterial attachment, biofilm detachment, and regrowth kinetics determined from changes in the areas of bands associated with proteins and polysaccharides were directly dependent on the DOC level. Furthermore, they were consistent with bacterial adhesion or growth kinetic models and extracellular polymeric substance overproduction or starvation-dependent detachment mechanisms.
Deciphering the mechanism of Alzheimer’s disease is a key element for designing an efficient therapeutic strategy. Molecular dynamics (MD) calculations, atomic force microscopy, and infrared ...spectroscopy were combined to investigate β-amyloid (Aβ1–42) peptide interactions with supported lipid bilayers (SLBs). The MD simulations showed that nascent Aβ1–42 monomers remain anchored within a model phospholipid bilayer’s hydrophobic core, which suggests their stability in their native environment. We tested this prediction experimentally by studying the behavior of Aβ1–42 monomers and oligomers when interacting with SLBs. When Aβ1–42 monomers and oligomers were self-assembled with a lipid bilayer and deposited as an SLB, they remain within the bilayers. Their presence in the bilayers induces destabilization of the model membranes. No specific interactions between Aβ1–42 and the SLBs were detected when SLBs free of Aβ1–42 were exposed to Aβ1–42. This study suggests that Aβ can remain in the membrane after cleavage by γ-secretase and cause severe damage to the membrane.
Glycogen is mainly found as the principal storage form of glucose in cells. Many bacteria are able to synthesize large amounts of glycogen under unfavorable life conditions. By combining infrared ...spectroscopy, single molecule force spectroscopy (SMFS) and immuno-staining technique, we evidenced that planktonic P. fluorescens (Pf) cells are also able to produce glycogen as an extracellular polymeric substance. For this purpose, Pf suspensions were examined at 3 and 21 h of growth in nutritive medium (LB, 0.5 g/L). The conformation of the extracellular glycogen, revealed through its infrared spectral signature, has been investigated by SMFS measurements using Freely Jointed Chain model. The analysis of force versus distance curves showed over growth time that the increase of glycogen production was accompanied by an increase in glycogen contour lengths and ramifications. These results demonstrated that the production of extracellular bacterial glycogen can occur even if the cells are not subjected to unfavorable life conditions.
Extracellular polymeric substances (EPS) play an important role in biofilm cohesion and adhesion to surfaces. EPS of a P. fluorescens biofilm were characterized through their vibrational spectra ...(infrared and Raman) and their conformational properties using single molecule force spectroscopy with specific probes for glucose, galactose, and N-acetyl glucosamine-rich EPS. Vibrational spectra evidenced the overproduction of glycogen and other carbohydrates in the biofilm. The conformational analysis was performed from both the freely jointed chain (FJC) and worm like chain (WLC) models. The results of the FJC fittings showed highly ramified and/or folded structures for all the detected EPS with molecular elongations up to 1000–2500 nm, and typical Kuhn lengths of glycogen macromolecules. The characteristics of galactose-rich EPS have been found to be significantly different from those of glucose- and N-acetyl glucosamine-rich EPS. On the basis of the theoretical fittings with the WLC model, our results suggested that carbohydrates may be associated with peptide domains.
Antimicrobial peptides (AMPs) are currently known for their potential as an alternative to conventional antibiotics and new weapons against drug-resistant bacteria and biofilms. In the present work, ...the mechanism of action of a cyclic (colistin) and a linear (catestatin) AMP on a young E. coli biofilm was deciphered from the molecular to the cellular scale. To this end, infrared spectroscopy (attenuated total reflection–Fourier transform infrared) assisted by chemometric analysis was combined with fluorescence and atomic force microscopies to address the very different behaviors of both AMPs. Indeed, the colistin dramatically damaged the bacterial cell wall and the metabolism even though its action was not homogeneous over the whole bacterial population and repopulation can be observed after peptide removal. Conversely, catestatin did not lead to major damages in the bacterial morphology but its action was homogeneous over the whole bacterial population and the cells were unable to regrow after the peptide treatment. Our results strongly suggested that contrary to the cyclic molecule, the linear one is able to cause irreversible damages in the bacterial membrane concomitantly to a strong impact on the bacterial metabolism.
For several decades now, modulating and controlling the mechanical properties of hydrogels, and in particular exponentially growing polyelectrolyte multilayer films (PEMs), have been a major ...challenge, given their importance in a wide range of applications, including tissue engineering, implantable biomaterials, and drug delivery systems. In this work, we compared the cross-linking reaction of hydrogels based on the association of poly(allylamine) (PAH) and hyaluronic acid (HA) with either 1,4-butanediol diglycidyl ether (BDDE) or divinyl sulfone (DVS) at different concentrations. On the basis of infrared data analysis by means of a chemometric method, we demonstrated that the cross-linking reaction led to significant changes in their chemical features. We deciphered how the affinity of each cross-linker to alcohol and amino chemical functions drives the chemical features of the PEMs. These features can be described by a linear combination of pure HA-BDDE, PAH-BDDE or HA-DVS, and PAH-DVS-based hydrogels with ratios of 80 and 16% for the BDDE and 55 and 45% for the DVS reactions, respectively. Furthermore, the mechanical properties resulting from the BDDE cross-linking reaction were consistent with a high mechanical contribution of HA-BDDE, as estimated by the chemometric analysis. However, this linear combination cannot be applied for DVS. Indeed, the cross-linked PEM was softer than expected, regarding the chemical contributions of HA-DVS and PAH-DVS. Our results show that it is possible to control the mechanical and chemical features by the choice of the cross-linkers alone or in a mixture.
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