Abstract Iron plays a key role in cloud aqueous phase chemistry as it is a major source hydroxyl radical (HO•) due to Fenton and Photo-Fenton reactions. In cloud waters it has been shown that, although the environment is highly oxidant, both Fe (II) and Fe(III) are present. This result suggests that most of iron is under the form of organic complexes. These complexes would stabilize iron in its reduced form Fe(II) preventing it to be re-oxidized. In atmospheric chemistry models, the iron-oxalate complex is used to as a model of organic complexes. However iron could be chelated by other organic ligands from biological origin in cloud waters such as HULIS, EPSs or siderophores as observed in sea waters and more recently in rainwaters.
As it has been shown that living microorganisms are present in cloud waters, they potentially need to acquire iron from this environment by synthetizing siderophores.
In order to test this hypothesis we have isolated 458 strains (bacteria and yeast) from clouds collected at the puy de Dôme station (1465 m, France). These strains have been identified and screened for their in-lab production of siderophores. For this purpose the CAS (Chrome Azurol S) method has been adapted for 96 wells microplates in order to get a high-throughput detection method. This test allowed a quantitative evaluation of the siderophore production and a qualitative determination of the chelating functional groups (catechol, hydroxamate, carboxylate). 42% of the tested microbial isolates were able to produce siderophores.
Our results as discussed in terms of the implication of the presence of siderophores in clouds for atmospheric chemistry.
Aknowledgements:
This work is funded by the French ANR program « BIOCAP » and CNRS EC2CO.
N. Wirgot is a recipient of a PhD grant from the MESNR.