Siderophores in Cloud Waters and Potential Impact on Atmospheric Chemistry: Production by Microorganisms Isolated at the Puy de Dôme Station.

A total of 450 bacteria and yeast strains isolated from cloud waters sampled at the puy de Dôme station in France (1465 m) were screened for their ability to produce siderophores. To achieve this, a high-throughput method in 96-well plates was adapted from the CAS (chrome azurol S) method. Notably, 42% of the isolates were siderophore producers. This production was examined according to the phyla of the tested strains and the type of chelating functional groups (i.e., hydroxamate, catechol, and mixed type). The most active bacteria in the clouds belong to the γ-Proteobacteria class, among which the Pseudomonas genus is the most frequently encountered. γ-Proteobacteria are produced in the majority of mixed function siderophores, such as pyoverdines, which bear a photoactive group. Finally, siderophore production was shown to vary with the origin of the air masses. The organic speciation of iron remains largely unknown in warm clouds. Our results suggest that siderophores could partly chelate Fe(III) in cloud waters and thus potentially impact the chemistry of the atmospheric aqueous phase.

In situ thermal denaturation of myofibre sub-type proteins studied by immunohistofluorescence and synchrotron radiation FT-IR microspectroscopy.

The thermal denaturation of proteins in skeletal muscle was studied and characterised for the first time taking into account the in situ metabolic and contractile fibre types. From serial histological sections, collagen, elastin, various type I, IIa and IIx fibres and type I-IIa and IIa-IIx hybrids were identified by immunohistofluorescence. Histological sections were incubated in buffer solutions at increasing temperatures (40, 50, 60, 70 and 80°C). Protein secondary structure was investigated by synchrotron radiation FT-IR microspectroscopy on connective tissue and in muscle fibres rigorously identified for sub-type. Whatever the target protein components, increasing temperature resulted in a decrease in α-helix secondary structure and an increase in ß-sheet structure. This phenomenon was more pronounced for intracellular proteins than for connective tissue. Although hybrid fibres were generally somewhat less sensitive to unfolding than the pure types, the amplitude of the thermal denaturation of intracellular proteins was practically independent of fibre type.