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Project Progress

The primary focus of the past 12 months has been on minerals generated by iron-oxidizing bacteria at neutral pH and on sulfate-reducing bacteria. We have continued to characterize the products of a diversity of iron-oxidizing bacteria and discovered that polymer mineralization can yield unexpected mineral phases with extreme morphologies not encountered in inorganic materials. Specifically, recrystallization on extracellular polymer strands generates akaganeite pseudo-single crystals with aspect ratios of > 1000:1. Until recently, we had presumed that these features arose due to polymer directed mineral growth. In the past few months we have analyzed these biogenic materials with two different X-ray microscopies and have been able to confirm the presence of organic carbon and establish that the polymers are predominantly saccharides. We have postulated a direct connection between mineralization and energy metabolism to explain the investment by bacteria in production of these polymers. Nature has encouraged submission of manuscript reporting these data. We have redeveloped oligonucleotide probes for detection of sulfate-reducing bacteria and used these to characterize biofilms. We have completed a description of the structure, microstructure, and aggregation state of metal sulfides formed as the direct result of sulfate-reducing bacteria (SRB) activity. The data imply episodic mineralization, possibly arising to oscillatory system behavior because of the effects of completing metabolic pathways for sulfate and organic carbon utilization. A manuscript reporting these data is about to be submitted.