Iron removal from raw asbestos by siderophores-producing Pseudomonas

Asbestos, mineral present in soil, are highly toxic due to the presence of iron. Microbes-mineral interactions occur naturally through various processes leading to their alteration. We examined the effect of siderophore-producing Pseudomonas with a particular focus on the role of pyoverdine and pyochelin on raw asbestos fibers such as amosite, crocidolite and chrysotile. We compared the efficiency of pyoverdine to the iron chelating agent EDTA in the release of iron from raw asbestos fibers. Pyoverdine was able to extract iron from all the tested raw asbestos with the higher efficiency observed for chrysotile and crocidolite. When asbestos were grinded, the iron removal was more important for all types. We monitored the effect of bacterial growth and siderophores containing bacterial supernatant on raw asbestos dissolution by solution chemistry analysis and transmission electron microscopy. The siderophore-containing supernatant allowed a higher iron solubilisation than the one obtained after bacterial growth. Moreover, the iron dissolution was faster with pyoverdine-containing supernatant than pyochelin-containing supernatant, with approximately the same iron level for the maximum extraction with a delay of 48 h. Our study clearly showed the involvement of bacterial siderophores, pyoverdine and pyochelin on chrysotile, crocidolite and amosite fibers weathering.