The role of manganese- and iron-oxidizing bacteria in the cycling of iron and manganese is a critical question in geomicrobiology, especially in habitats such as marine nodules, cave ferromanganese deposits, and desert/rock varnish. While it is well recognized that these elements are involved in biogeochemical cycling, careful work (with a multidisciplinary approach including molecular biology, high-resolution mineralogy and geochemistry, and innovative environmental sampling) is necessary to establish the active role of microbes in the mineral accumulations of these elements. Many aspects of these processes are not well understood and much remains to be done to establish that these deposits are truly biogenic. The investigators have assembled a multidisciplinary team to investigate the microbial and abiotic processes that produce these ferromanganese deposits.
Previously the investigators have established that (1) ferromanganese deposits coat the walls and ceiling of Lechuguilla and Spider Caves in areas where there are no macro-organisms; (2) bacteria that are able to form manganese and iron oxides in enrichment cultures live in remote areas of Lechuguilla and Spider Caves; (3) the formation of manganese minerals in culture progresses from amorphous to crystalline Fe and Mn mineral forms over 8-10 months in preliminary studies; and (4) phylogenetic studies have established that organisms from the natural materials and isolated cultures group with known iron and manganese oxidizers, but are not closely related.
To further elucidate the role(s) of iron- and manganese-oxidizing bacteria in the formation of ferromanganese deposits, the proposed research will: 1. Determine the progression of mineral transformation in iron and manganese enrichment cultures inoculated with cave ferromanganese deposits. 2. Investigate whether similar transformations occur in rock varnish iron and manganese enrichment cultures. 3. Compare these transformation products (minerals) to natural ferromanganese deposit mineral forms occurring in caves and rock varnish. 4. Characterize the microbial species involved in the production of these minerals in culture. 5. Determine whether previously characterized putative manganese-oxidizing genes are present in organisms found in iron and manganese enrichment cultures.
Information from the proposed investigations will elucidate how microbial life flourishes in this dark, low-nutrient environment, producing an abundance of ferromanganese deposits over geological time scales. Details of the processes and the identities of the players that help produce these ferromanganese deposits in caves and in rock varnish will be determined and additional novel organisms will likely be documented from these deposits. Results from the proposed research will provide insight into the geological alterations of iron and manganese by microorganisms and will help to resolve unknown aspects of these alterations.
