Pupa Gilbert (née Gelsomina De Stasio)
Research Group

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Electron micrograph of clusters of bacterial produced ZnS nanoparticles (yellow) in a biofilm from Tennyson, WI. Cover of Science, 270, 1744 (2000).
Geomicrobiology is the science that studies the interaction between microorganisms and minerals in their environment. Not only can microorganisms live in inhospitable environments, but they can also extract energy for life from inorganic chemistry. Such interactions can affect geological cycles, causing mineral precipitation or dissolution in a wide range of niches.
          We collaborated with Jill Banfield and Matthias Labrenz, at the Geology Department, UW-Madison, studying the metabolism of ZnS precipitating bacteria. In aqueous niches in which oxygen is in short supply, so-called sulfur reducing bacteria can couple their metabolism to the formation of metal sulfides. Recent work by Jill's group, showed that a novel family of this bacterium in a flooded zinc mine in Tennyson, WI causes the precipitation of zinc sulfide1 as nanocrystals. The tiny precipitates aggregate and form micron size clusters - shown yellow in the figure.
          Despite the presence of many metal ions besides zinc, the precipitate is very pure. In addition, the tiny ZnS particles come in dimensions as small as 1 nm, a type of nano-sized material only recently synthesized by inorganic chemistry methods. For a detailed description of this work, go to Jill Banfield's web site.
          Spectromicroscopy studies demonstrated that particles associated with the bacteria contained zinc sulfide, and also showed that sulfate ions were ubiquitous in solution2. The detection of sulfur in both chemical states corroborated the hypothesis that the bacteria convert sulfate dissolved in the water into sulfide, which rapidly forms tiny insoluble particles, the beginning of a zinc ore. Wet chemistry work, performed by Jill Banfield and her group, elucidated the complete bacterial metabolism.
          We also collaborated with Ken Nealson, Pan Conrad and Andrea Belz, studying bacteria that oxidize manganese2; and with Susanne Douglas on cyanobacteria3.

  1. M. Labrenz, G.K. Druschel, T. Thomsen-Ebert, B. Gilbert, S.A. Welch, K.M. Kemner, G.A. Logan, R.E. Summons, G. De Stasio, P.L. Bond, B. Lai, S.D. Kelly, and J.F. Banfield. Sphalerite (ZnS) deposits forming in natural biofilms of sulfate-reducing bacteria. Science, 270, 1744-1747 (2000).

  2. B. Gilbert, G. Margaritondo, S. Douglas, K. H. Nealson, R. F. Edgerton, G. Rempfer, G. De Stasio, XANES microspectroscopy of biominerals with photoconductive charge compensation, J. Electr. Spectrosc. and Rel Phenom. 114/116 (1-3), 1005-1011, 2001.

  3. B. Gilbert, B.H. Frazer, A. Belz, P. Conrad, K. H. Nealson, D. Haskel, J.C. Lang, G. Srajer and G. De Stasio, Multiple scattering calculations of bonding and X-ray absorption spectroscopy of manganese oxides. Journal of Physical Chemistry A, 107, 2839-2847 (2003).