Morphology of biogenic iron oxides records microbial physiology and environmental conditions; toward interpreting iron microfossils

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doi: 10.1111/gbi.12043
Author(s): Krepski, S. T.; Emerson, D.; Hredzak-Showalter, P. L.; Luther, G. W., III; Chan, C. S.
Author Affiliation(s): Primary:
University of Delaware, Department of Geological Sciences, Newark, DE, United States
Bigelow Laboratory for Ocean Sciences, United States
Volume Title: Geobiology
Source: Geobiology, 11(5), p.457-471. Publisher: Blackwell, Oxford, United Kingdom. ISSN: 1472-4677
Note: In English. 64 refs.; illus.
Summary: Despite the abundance of Fe and its significance in Earth history, there are no established robust biosignatures for Fe(II)-oxidizing micro-organisms. This limits our ability to piece together the history of Fe biogeochemical cycling and, in particular, to determine whether Fe(II)-oxidizers played a role in depositing ancient iron formations. A promising candidate for Fe(II)-oxidizer biosignatures is the distinctive morphology and texture of extracellular Fe(III)-oxyhydroxide stalks produced by mat-forming microaerophilic Fe(II)-oxidizing micro-organisms. To establish the stalk morphology as a biosignature, morphologic parameters must be quantified and linked to the microaerophilic Fe(II)-oxidizing metabolism and environmental conditions. Toward this end, we studied an extant model organism, the marine stalk-forming Fe(II)-oxidizing bacterium, Mariprofundus ferrooxydans PV-1. We grew cultures in flat glass microslide chambers, with FeS substrate, creating opposing oxygen/Fe(II) concentration gradients. We used solid-state voltammetric microelectrodes to measure chemical gradients in situ while using light microscopy to image microbial growth, motility, and mineral formation. In low-oxygen (2.7-28 µm) zones of redox gradients, the bacteria converge into a narrow (100 µm-1 mm) growth band. As cells oxidize Fe(II), they deposit Fe(III)-oxyhydroxide stalks in this band; the stalks orient directionally, elongating toward higher oxygen concentrations. M. ferrooxydans stalks display a narrow range of widths and uniquely biogenic branching patterns, which result from cell division. Together with filament composition, these features (width, branching, and directional orientation) form a physical record unique to microaerophilic Fe(II)-oxidizer physiology; therefore, stalk morphology is a biosignature, as well as an indicator of local oxygen concentration at the time of formation. Observations of filamentous Fe(III)-oxyhydroxide microfossils from a ∼170 Ma marine Fe-Si hydrothermal deposit show that these morphological characteristics can be preserved in the microfossil record. This study demonstrates the potential of morphological biosignatures to reveal microbiology and environmental chemistry associated with geologic iron formation depositional processes. Abstract Copyright (2013), John Wiley & Sons, Ltd.
Year of Publication: 2013
Research Program: ODP Ocean Drilling Program
Key Words: 01 Mineralogy and Crystallography; 09 Paleontology, Paleobotany; Bacteria; Biogenic processes; Biomarkers; Experimental studies; Hydroxides; Iron oxides; Jurassic; Laboratory studies; Living taxa; Mariprofundus ferrooxydans; Mesozoic; Microfossils; Middle Jurassic; Modern analogs; Morphology; North Pacific; Northwest Pacific; ODP Site 801; Ocean Drilling Program; Oxidation; Oxides; Oxyhydroxides; Pacific Ocean; Physiology; Pigafetta Basin; West Pacific
Coordinates: N183831 N183835 E1562136 E1562134
Record ID: 2015005724
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from John Wiley & Sons, Chichester, United Kingdom