Studies of Iron Bacteria

Verification of surficial bodies of water in the Martian past by NASA's Mars Exploration Rovers (MER) have raised the probability for past life and the prospect of actually finding fossilized Martian life forms. Considering that life on Earth was microbial for several billion years, and that Mars apparently lost the bulk of its water during the first 1 billion years, it is reasonable to assume that if we do find traces of past Martian life, it should be microbial in nature. Chemical and mineralogical information returned by the MER missions indicates a crust of an overall basaltic and Fe-rich composition and sulfate-rich waters. Because all life is opportunistic, one may reasonably expect that Martian microbes would have exploited the available surface chemistry, for example by adopting sulfate reducing and iron oxidizing metabolic pathways. With abundant CO2 in the atmosphere, to think of past Martian life as carbon based is plausible as well.
We currently are working on microbial mats produced by iron bacteria in a small creek south of Bloomington, Indiana. We are interested in mat accretion and the potential to form preservable biolaminated deposits, in fossilization of iron microbes in various diagenetic environments, and in isotopic biosignatures we might find in sediments containing remains of iron bacteria. The following images are power point slides from a presentation at the 2004 Lunar and Planetary Science Conference.
These mats form dense felts that cover the creek bottom and are heavily dominated by the iron bacterium Leptothrix. The free swimming iron bacterium Gallionella is also common and recognized by its corkscrew stalks.
The microbial buildups grow preferentially in upstream direction, and grow best where we have the largest flow rates.
Iron mineralization of Leptothrix sheaths and Gallionella stalks makes them mechanically more resistant. Material that is washed downstream from active mats shows good morphological preservation.
The iron mineralization also provides morphological preservation when the very water-rich mat materials are dried.

References for above:

Schieber, J., 2004. Groundwater-Fed Iron-Rich Microbial Mats in a Freshwater Creek: Growth Cycles and Fossilization Potential of Microbial Features.  35th Lunar and Planetary Sciences Conference, Houston, March 15-19st 2004, Abstract Volume - CD. download PDF file (left click on link and click on "Save as"...)

Strapoc, D., and Schieber, J., 2004. Carbon Isotope Characteristics of Spring-Fed Iron-Precipitating Microbial Mats.  35th Lunar and Planetary Sciences Conference, Houston, March 15-19st 2004, Abstract Volume - CD.  (left click on link and click on "Save as"...) download PDF file

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© Jürgen Schieber, IU Bloomington Department of Geosciences
Last updated: December 10, 2006.