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This study evaluates rates and pathways of methane (CH4) oxidation and uptake using 14C-based tracer experiments throughout the oxic and anoxic waters of ferruginous Lake Matano. Methane oxidation rates in Lake Matano are low compared to other lakes, but are sufficiently high to preclude strong CH4 fluxes to the atmosphere. In addition to aerobic CH4 oxidation, which takes place in Lake Matano's oxic mixolimnion, we also detected CH4 oxidation in Lake Matano's anoxic ferruginous waters. Here, CH4 oxidation proceeds in the apparent absence of oxygen (O2) and instead appears to be coupled to nitrate (NO3-), nitrite (NO2-), iron (Fe), or manganese (Mn) reduction. Throughout the lake, the fraction of CH4 carbon that is assimilated vs. oxidized to carbon dioxide (CO2) is high, indicating extensive CH4 conversion to biomass and underscoring the importance of CH4 as a carbon and energy source in Lake Matano and potentially other ferruginous or low productivity environments. [ABSTRACT FROM AUTHOR]

In Lake Matano, Indonesia, the world's largest known ferruginous basin, more than 50% of authigenic organic matter is degraded through methanogenesis, despite high abundances of Fe (hydr)oxides in the lake sediments. Biogenic CH accumulates to high concentrations (up to 1.4 mmol L) in the anoxic bottom waters, which contain a total of 7.4 × 10 tons of CH. Profiles of dissolved inorganic carbon (ΣCO) and carbon isotopes (δC) show that CH is oxidized in the vicinity of the persistent pycnocline and that some of this CH is likely oxidized anaerobically. The dearth of NO and SO in Lake Matano waters suggests that anaerobic methane oxidation may be coupled to the reduction of Fe (and/or Mn) (hydr)oxides. Thermodynamic considerations reveal that CH oxidation coupled to Fe(III) or Mn(III/IV) reduction would yield sufficient free energy to support microbial growth at the substrate levels present in Lake Matano. Flux calculations imply that Fe and Mn must be recycled several times directly within the water column to balance the upward flux of CH. 16S gene cloning identified methanogens in the anoxic water column, and these methanogens belong to groups capable of both acetoclastic and hydrogenotrophic methanogenesis. We find that methane is important in C cycling, even in this very Fe-rich environment. Such Fe-rich environments are rare on Earth today, but they are analogous to conditions in the ferruginous oceans thought to prevail during much of the Archean Eon. By analogy, methanogens and methanotrophs could have formed an important part of the Archean Ocean ecosystem. [ABSTRACT FROM AUTHOR]

The article discusses various reports in this issue including one about bacterial metabolism and another about microbiological activity in carbonate and clay mineralization.

The reduction of Fe during bacterial anaerobic respiration in sediments and soils not only causes the degradation of organic matter but also results in changes in mineralogy and the redistribution of many nutrients and trace metals. Understanding trace metal patterns in sedimentary rocks and predicting the fate of contaminants in the environment requires a detailed understanding of the mechanisms through which they are redistributed during Fe reduction. In this work, lacustrine sediments from Lake Matano in Indonesia were incubated in a minimal media with the dissimilatory iron reducing (DIR) bacterium Shewanella putrefaciens 200R. These sediments were reductively dissolved at rates slower than pure synthetic goethite despite the presence of an ‘easily reducible’ component, as defined by selective extractions. DIR of the lacustrine sediments resulted in the substrate-dependent production of abundant quantities of extracellular polymeric substances. Trace elements, including Ni, Co, P, Si, and As, were released from the sediments with progressive Fe reduction while Cr was sequestered. Much of the initial trace metal mobility can be attributed to the rapid reduction of a Mn-rich oxyhydroxide phase. The production of organo-Fe(III) reveals that DIR bacteria can generate significant metal complexation capacity. This work demonstrates that DIR induces the release of many elements associated with Fe-Mn oxyhydroxides, despite secondary mineralization. [ABSTRACT FROM AUTHOR]

The first fully energy-minimized structures for a series of structurally related metal complexes of the important mammalian metal binding protein metallothionein are described. The structures were calculated based on structural information obtained from existing spectroscopic and crystallographic data, and minimized using molecular mechanics (MM2) techniques. A two domain structure, with stoichiometries of M(II)3-(Scys)9 and M(II)4-(Scys)11 where M = zinc(II), cadmium(II), and mercury(II), was assembled and minimized. The resultant three-dimensional structure closely resembled that of rat liver Cd5Zn2-MT 1 obtained by analysis of x-ray diffraction data [A. H. Robbins, D.E. McRee, M. Williamson, S. A. Collett, N. H. Xuong, W. F. Furey, B. C. Wang and C. D. Stout, J. Mol. Biol. 221, 1269-1293 (1991)]. Minimized structures for Zn7-MT, Cd7-MT, and Hg7-MT are reported. Deep crevices that expose the metal-thiolate clusters are seen in each structure. However, for the mercury-containing protein, much of the mercury-thiolate structure is visible and it is proposed that this provides access for extensive interaction between solvent water molecules and the mercury(II), resulting in the observed distortion away from tetrahedral geometry for Hg7-MT. Volume calculations are reported for the protein metallated with 7 Zn(II), Cd(II), or Hg(II). A series of structural changes calculated for the step-wise isomorphous replacement of Zn(II) by Cd(II) and Hg(II) in the Zn4S11 alpha domain are shown.