Biodeterioration of asbestos cement by siderophore-producing Pseudomonas

Since the ban on the use of asbestos due to its carcinogenic properties, the removal of asbestos cement, representing the major asbestos-containing waste, has proven to be a challenge in most industrial countries. Asbestos-containing products are mainly disposed of in landfills and have remained untreated. Bioremediation involving bacteria previously reported the ability of Pseudomonas aeruginosa to release iron from flocking asbestos waste through a siderophore-driven mechanism. We examined the involvement of siderophore-producing Pseudomonas in the biodeterioration of asbestos cement. Iron and magnesium solubilization were evaluated by specific siderophore-producing mutants. The absence of one of the two siderophores affected iron extraction, whereas equivalent dissolution as that of the control was observed in the absence of siderophore. Both pyoverdine and pyochelin biosynthesis was repressed in the presence of asbestos cement, suggesting iron bioavailability from the waste. We compared the efficiency of various pyoverdines to scavenge iron from asbestos cement waste that revealed the efficiency of all pyoverdines. Pyoverdines were efficient in iron removal extracted continuously, with no evident extraction limit, in long-term weathering experiments with these pyoverdines. The optimization of pyoverdine-asbestos weathering may allow the development of a bioremediation process to avoid the disposal of such waste in landfills.