The Role of Siderophores in Iron Oxide Dissolution

For over 50 years microbiologists have been aware of a class of compounds, produced by microorganisms, called siderophores. This chapter examines the type of Iron(Fe) to which siderophores bind and the location where they do so. The assumption in the literature has been that the purpose of siderophores is to supply Fe to the cell-so often stated that this quote is rarely referenced. Even though the dissolution of Fe oxides has been reviewed extensively in the literature, it is worthwhile to briefly review dissolution mechanisms, since they apply to the potential involvement of siderophores. In a study, Fe release and siderophore production by Azotobacter vinelandii (a gram-negative, asymbiotic nitrogen-fixing soil bacterium with an absolute requirement for Fe) was investigated by using several Fe oxide minerals as sources of Fe. Undoubtedly, siderophores are used by microorganisms to acquire Fe and are produced by microorganisms in response to a limited availability of Fe. These two observations are supported by hundreds of publications in the open literature. However, the results discussed in the chapter suggest that siderophores may not be entirely responsible for Fe oxide dissolution, that the role that siderophores play in the dissolution of Fe oxides remains unclear, and thus that the microbial dissolution of Fe oxides merits further investigation.