HR: 11:20h
AN: B22D-05    [Abstracts]
TI: Biochemistry and Ecology of Novel Cytochromes Catalyzing Fe(II) Oxidation by an Acidophilic Microbial Community
AU: * Singer, S W
EM: singer2@llnl.gov
AF: Chemistry, Materials and Life Sciences Directorate, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550,
AU: Jeans, C J
EM: jeans2@llnl.gov
AF: Chemistry, Materials and Life Sciences Directorate, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550,
AU: Thelen, M P
EM: thelen1@llnl.gov
AF: Chemistry, Materials and Life Sciences Directorate, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550,
AU: VerBerkmoes, N C
EM: verberkmoesn@ornl.gov
AF: Chemical Sciences Division, Oak Ridge National Laboratory, 1 Bethel Valley Road Bldg 4500S, MS-6129, Oak Ridge, TN 37831,
AU: Hettich, R C
EM: hettichrl@ornl.gov
AF: Chemical Sciences Division, Oak Ridge National Laboratory, 1 Bethel Valley Road Bldg 4500S, MS-6129, Oak Ridge, TN 37831,
AU: Chan, C S
EM: cchan@whoi.edu
AF: Department of Earth and Planetary Sciences, University of California, Berkeley, 307 McCone Hall, Berkeley, CA 94720,
AU: Banfield, J F
EM: jbanfield@berkeley.edu
AF: Department of Earth and Planetary Sciences, University of California, Berkeley, 307 McCone Hall, Berkeley, CA 94720,
AB: An acidophilic microbial community found in the Richmond Mine at Iron Mountain, CA forms abundant biofilms in extremely acidic (pH<1) and toxic metal conditions. In this ecosystem, biological Fe(II) oxidation is critical to the metabolic functioning of the community, and in turn this process generates acid mine drainage, causing an environmental catastrophe. Two conspicuous novel proteins isolated from these biofilms were identified as gene products of Leptospirillum group II and were characterized as cytochromes with unique properties. Sulfuric acid extraction of biofilm samples liberated one of these proteins, a 16 kDa cytochrome with an unusual alpha-band absorption at 579 (Cyt579). Genomic sequencing of multiple biofilms indicated that several variants of Cyt579 were present in Leptospirillum strains. Intact protein MS analysis identified the dominant variants in each biofilm and documented multiple N-terminal cleavage sites for Cyt579. By combining biochemical, geochemical and microbiological data, we established that the sequence variation and N-terminal processing of Cyt579 are selected by ecological conditions. In addition to the soluble Cyt579, the second cytochrome appears as a much larger protein complex of ~210 kDa predominant in the biofilm membrane fraction, and has an alpha-band absorption at 572 nm. The 60 kDa cytochrome subunit, Cyt572, resides in the outer membrane of LeptoII, and readily oxidizes Fe(II) at low pH (0.95 - 3.0). Several genes encoding Cyt572 were localized within a recombination hotspot between two strains of LeptoII, causing a large range of variation in the sequences. Genomic sequencing and MS proteomic studies established that the variants were also selected by ecological conditions. A general mechanistic model for Fe(II) oxidation has been developed from these studies. Initial Fe(II) oxidation by Cyt572 occurs at the outer membrane. Cyt572 then transfers electrons to Cyt579, perhaps representing an initial step in energy flow to the biofilm community. Amino acid variations and post-translational modifications of these unique cytochromes may represent fine-tuning of function in response to local environmental conditions.
DE: 0448 Geomicrobiology
DE: 0461 Metals
DE: 0465 Microbiology: ecology, physiology and genomics (4840)
DE: 0471 Oxidation/reduction reactions (4851)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting