Kurt Konhauser

Knoll/Fundamentals of Geobiology, 2012

Role of Microorganisms in Banded Iron Formations

Geomicrobiology: Molecular and Environmental Perspective, 2010

Bacterial Biomineralization

Knoll/Fundamentals of Geobiology, 2012

The electrochemical variability of cyanobacterial surfaces Fe(II) adsorption at the cell-water interface: From macroscopic observations to spectroscopic measurements

Bacterial surfaces act as efficient metal scavangers with important roles in a variety of geochem... more Bacterial surfaces act as efficient metal scavangers with important roles in a variety of geochemical processes. As a result, surface complexation models have been used in an to attempt to develop quantitative and predictive tools with broad relevancy. Such models have aimed to quantify the extent of metal and proton adsorption to bacteria by relying on established thermodynamic and mass balance data used in combination with experimentally-derived surface site functional group concentrations and deprotonation constants. Daugney et al. (2001) were the first to consider potential biological sources of error in such experimentally derived data by showing that different growth phases of Bacillus subtilis led to variations in ligand concentrations and metal sorption. In order to identify potentially important biological variations more relevant to natural systems, we grew the heterocyst forming, filamentous and nonsheathed cyanobacteria Anabaena sp. PCC7120 on various nitrogen sources, a...

Benthic perspective on Earth's oldest evidence for oxygenic photosynthesis

Modes of Biomineralization of Magnetite by Microbes

Proceedings of the National Academy of Sciences of the United States of America, Jan 27, 2015

The Great Oxidation Event (GOE) is currently viewed as a protracted process during which atmosphe... more The Great Oxidation Event (GOE) is currently viewed as a protracted process during which atmospheric oxygen increased above ∼10(-5) times the present atmospheric level (PAL). This threshold represents an estimated upper limit for sulfur isotope mass-independent fractionation (S-MIF), an Archean signature of atmospheric anoxia that begins to disappear from the rock record at 2.45 Ga. However, an increasing number of papers have suggested that the timing for oxidative continental weathering, and by conventional thinking the onset of atmospheric oxygenation, was hundreds of million years earlier than previously thought despite the presence of S-MIF. We suggest that this apparent discrepancy can be resolved by the earliest oxidative-weathering reactions occurring in benthic and soil environments at profound redox disequilibrium with the atmosphere, such as biological soil crusts and freshwater microbial mats covering riverbed, lacustrine, and estuarine sediments. We calculate that oxyge...

Geomicrobiology Journal, 2007

Biomineralization processes have traditionally been grouped into two distinct modes; biologically... more Biomineralization processes have traditionally been grouped into two distinct modes; biologically induced mineralization (BIM) and biologically controlled mineralization (BCM). In BIM, microbes cause mineral formation by sorbing solutes onto their cell surfaces or extruded organic polymers and/or releasing reactive metabolites which alter the saturation state of the solution proximal to the cell or polymer surface. Such mineral products appear to

Atmospheric hydrogen peroxide and Eoarchean iron formations

It is widely accepted that photosynthetic bacteria played a crucial role in Fe(II) oxidation and ... more It is widely accepted that photosynthetic bacteria played a crucial role in Fe(II) oxidation and the precipitation of iron formations (IF) during the Late Archean-Early Paleoproterozoic (2.7-2.4 Ga). It is less clear whether microbes similarly caused the deposition of the oldest IF at ca. 3.8 Ga, which would imply photosynthesis having already evolved by that time. Abiological alternatives, such as the direct oxidation of dissolved Fe(II) by ultraviolet radiation may have occurred, but its importance has been discounted in environments where the injection of high concentrations of dissolved iron directly into the photic zone led to chemical precipitation reactions that overwhelmed photooxidation rates. However, an outstanding possibility remains with respect to photochemical reactions occurring in the atmosphere that might generate hydrogen peroxide (H 2 O 2 ), a recognized strong oxidant for ferrous iron. Here, we modeled the amount of H 2 O 2 that could be produced in an Eoarchean atmosphere using updated solar fluxes and plausible CO 2 , O 2 , and CH 4 mixing ratios. Irrespective of the atmospheric simulations, the upper limit of H 2 O 2 rainout was calculated to be <10 6 molecules cm À2 s À1 . Using conservative Fe(III) sedimentation rates predicted for submarine hydrothermal settings in the Eoarchean, we demonstrate that the flux of H 2 O 2 was insufficient by several orders of magnitude to account for IF deposition (requiring~10 11 H 2 O 2 molecules cm À2 s À1 ). This finding further constrains the plausible Fe(II) oxidation mechanisms in Eoarchean seawater, leaving, in our opinion, anoxygenic phototrophic Fe(II)-oxidizing micro-organisms the most likely mechanism responsible for Earth's oldest IF.

The in situ molecular characterisation of a biomineralization process: a synchrotron infrared study

Silica colloid aggregation by cyanobacteria: A microbial silicification mechanism

Transition element abundances in Banded Iron Formations record the great Oxidation Event

The formation and preservation of Synechococcus elongatus cell molds in simulated silica sinter: implications for the identification of microfossils

Microbially-catalyzed cementation of modern gypsum-dominated thrombolites

Potential role of nitrite for abiotic Fe (II) oxidation and cell encrustation during nitrate reduction by denitrifying bacteria

Chromium enrichment in iron formations record Earth’s first acid rock drainage during the Great Oxidation Event

by Kurt Konhauser, S. Lalonde, and Stephen Mojzsis

Microorganisms have been observed to oxidize Fe(II) at neutral pH under anoxic and microoxic cond... more Microorganisms have been observed to oxidize Fe(II) at neutral pH under anoxic and microoxic conditions. While most of the mixotrophic nitrate-reducing Fe(II)-oxidizing bacteria become encrusted with Fe(III)-rich minerals, photoautotrophic and microaerophilic Fe(II) oxidizers avoid cell encrustation. The Fe(II) oxidation mechanisms and the reasons for encrustation remain largely unresolved. Here we used cultivation-based methods and electron microscopy to compare two previously described nitrate-reducing Fe(II) oxidizers (Acidovorax sp. strain BoFeN1 and Pseudogulbenkiania sp. strain 2002) and two heterotrophic nitrate reducers (Paracoccus denitrificans ATCC 19367 and P. denitrificans Pd 1222). All four strains oxidized ϳ8 mM Fe(II) within 5 days in the presence of 5 mM acetate and accumulated nitrite (maximum concentrations of 0.8 to 1.0 mM) in the culture media. Iron(III) minerals, mainly goethite, formed and precipitated extracellularly in close proximity to the cell surface. Interestingly, mineral formation was also observed within the periplasm and cytoplasm; intracellular mineralization is expected to be physiologically disadvantageous, yet acetate consumption continued to be observed even at an advanced stage of Fe(II) oxidation. Extracellular polymeric substances (EPS) were detected by lectin staining with fluorescence microscopy, particularly in the presence of Fe(II), suggesting that EPS production is a response to Fe(II) toxicity or a strategy to decrease encrustation. Based on the data presented here, we propose a nitrite-driven, indirect mechanism of cell encrustation whereby nitrite forms during heterotrophic denitrification and abiotically oxidizes Fe(II). This work adds to the known assemblage of Fe(II)-oxidizing bacteria in nature and complicates our ability to delineate microbial Fe(II) oxidation in ancient microbes preserved as fossils in the geological record.

Porosity and permeability in bioturbated sediments

Microbiological processes in banded iron formation deposition

Iron Formation: The Sedimentary Product of a Complex Interplay among Mantle, Tectonic, Oceanic, and Biospheric Processes

Economic Geology, 2010

The Microbial Role in Hot Spring Silicification

Ambio, 2004

Recent experimental studies indicate that microorganisms play a passive role in silicification. T... more Recent experimental studies indicate that microorganisms play a passive role in silicification. The organic functional groups that comprise the outer cell surfaces simply serve as heterogeneous nucleation sites for the adsorption of polymeric and/or colloidal silica, and because different microorganisms have different cell ultrastructural chemistry, species-specific patterns of silicification arise. Despite their templating role, they do not appear to increase the kinetics of silicification, and at the very most, they contribute only marginally to the magnitude of silicification. Instead, silicification is due to the polymerization of silicasupersaturated hydrothermal fluids upon discharge at the surface of the hot spring. Microorganisms do, however, impart an influence on the fabric of the siliceous sinters that form around hot spring vents. Different microorganisms have different growth patterns, that in turn, affect the style of laminations, the primary porosity of the sinter and the distribution of later-stage diagenetic cementation.