Microbially mediated formation of birnessite - type manganese oxides and subsequent incorporation of rare earth elements , Ytterby mine , Sweden

Microbes exert extensive control on redox element cycles. They participate directly or indirectly in the concentration and fractionation of elements by influencing the partitioning between soluble and insoluble species. Putative microbially mediated manganese (Mn) oxides of the birnessite-type, enriched in rare earth elements (REE) + yttrium (Y) were recently found in the Ytterby mine, Sweden. A poorly crystalline birnessite-type phyllomanganate is regarded as the predominant initial phase formed during microbial Mn oxidation. Owing to a higher specific surface area, this biomineral also enhances the known sorption property of Mn oxides with respect to heavy metals (e.g. REE) and therefore has considerable environmental impact. The concentration of REE + Y (2±0.5% of total mass, excluding oxygen, carbon and silicon) in the Ytterby Mn oxide deposit is among the highest ever observed in secondary precipitates with Mn and/or iron. Sequential extraction provides evidence of a mineral structure where the REE+Y are firmly included, even at pH as low as 1.5. Concentration ratios of Mn oxide precipitates to fracture water indicate a strong preference for the trivalent REE+Y over divalent and monovalent metals. A culture independent molecular phylogenetic approach was adopted as a first step to analyze the processes that microbes mediate in this environment and specifically how the microbial communities interact with the Mn oxides. Plausible players in the formation of the investigated birnessite-type Mn oxides are mainly found within the ferromanganese genera Hyphomicrobium and Pedomicrobium and a newly identified Ytterby Bacteroidetes cluster most closely related to the Terrimonas. Data also indicate that the detected microorganisms are related to the environmental constraints of the site including low constant temperature (8°C), absence of light, high metal content and possibly proximity to the former storage of petroleum products.