Biological influence on calcification and iron oxide formation

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Biomineralization processes are complex reactions induced by microorganisms for energy gain and / or by the effect their activity has on the microenvironment. In the previous funding period we have focused on microbially mediated iron precipitation using the Äspö Hard Rock Laboratory as a study site. We have used high‐throughput sequencing to analyze the microbial community in the system focusing our analysis on the diversity of ironoxidizing bacteria. We found large variations between the microbial communities fed by the 3 different aquifers tested. The data showed that the dominant iron oxidizing bacteria is not Gallionella, as previously assumed. Different dominant iron oxidizer are found at different locations in the tunnel (but Gallionella is never dominant). We found that bulk measure-ments of isotope‐labeled microbial mats underestimates iron oxidation rates by up to an order of magnitude. One reason is the internal iron cycling: oxidized iron is rapidly reduced biologically supplying additional Fe2+ for iron oxidation. The contribution of abiotic precipitation of iron to the mineralization process is high, but could not be accurately quantified. We will focus the coming 2 years on the fol-lowing issues:1) How does water chemistry determine the iron‐oxidizing community composition2) Is organic matter (EPS) or biotically‐precipitated iron the main nucleation site for abiotic iron precipitation within the biofilm3) What is the actual rate of iron cycling (Fe‐reduction coupled to oxidation).The proposed study aims to elucidate which environmental conditions control biotic and abiotic iron mineralization.