Analysis of changes in attenuated total reflection FTIR fingerprints of Pseudomonas fluorescens from planktonic state to nascent biofilm state

Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy is a useful method for monitoring biofilm in situ, non-destructively, in real time, and under fully hydrated conditions. In this work we focused on changes in Pseudomonas fluorescens ATR-FTIR fingerprint accompanying the very early stages of biofilm formation: initial bacterial adhesion and the very beginning of biofilm development in the presence of nutrients. To help interpreting variations in the ATR-FTIR fingerprint of sessile bacteria, ATR-FTIR spectra of planktonic bacteria in different growth phases were also examined, and the average surface coverage and spatial arrangement of bacteria on the ATR crystal were determined by epifluorescence microscopy. The proteins, nucleic acids and polysaccharides ATR-FTIR spectral data recorded during growth of sessile bacteria were shown to be linked to changes in the physiological state of the bacteria, possibly accompanied by extracellular polymeric substances production. This work clearly showed by spectroscopic method how bacteria change drastically their metabolism during the first hours of biofilm formation.     

In situ characterisation of a microorganism surface by Raman microspectroscopy: the shell of Ascaris eggs

Intestinal nematodes are very common human parasites and a single species, Ascaris lumbricoïdes, is estimated to infect a quarter of the world’s population. A sticky external layer covers their eggs. This work shows that Raman vibrational confocal spectroscopy is able to give information on the biochemical composition of the shell of Ascaris eggs. The biochemical localised characterisation of Ascaris eggs was performed directly on the eggs in their aqueous environment. The studied parasites came from two origins: dissections of adult females and extractions from biosolid sludges. The presence of mucopolysaccharides, proteins and chitin in the shell was demonstrated. The presence of ascaroside compounds was shown particularly via the narrow and intense bands from the organised long CH₂ chains. To the best of our knowledge, this is the first time that the latter have been observed in Raman vibrational spectra of microorganisms. Hydration of the shell was different depending on the intensity of the colour of the sludge eggs. Knowledge of the biochemical structural properties of egg surfaces would be useful to understand the egg adhesion phenomena on vegetables contaminated by reused wastewater.     

Hydrolysis of uranyl(VI) in acidic and basic aqueous solutions using a noncomplexing organic base: a multivariate spectroscopic and statistical study

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 (C(2)H(5))(4)NNO(3) at 25 °C and 0.1 MPa ([U(total)] = 0.005-0.105 M) in H(2)O and D(2)O over a wide range of -log mH(D)(+) between 2.92 and 14.50. Second, vibrational spectra (IR and Raman) of basic solutions in H(2)O and D(2)O were analyzed using the Bayesian Positive Source Separation method to estimate pure spectra of individual species. In D(2)O solutions, the new spectroscopic data showed the occurrence of the same species as those in H(2)O. As observed for the wavenumber of the symmetric stretching mode, the wavenumber characteristic of the O═U═O 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 UO(2)(OH)(4)(2-) and UO(2)(OH)(5)(3-) are confirmed to be in good agreement with earlier EXAFS and NMR results. The occurrence of the UO(2)(OH)(6)(4-) monomer is also suggested from the more basic solutions investigated.