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2011 Annual Science Report

Arizona State University Reporting  |  SEP 2010 – AUG 2011

Stoichiometry of Life - Task 2c - Biological Soil Crusts: Metal Use and Acquisition

Project Summary

Desert biological soil crusts (BSCs) are a complex consortia of microorganisms including cyanobacteria, algae, and fungi. BSCs are the primary colonizers of desert soils, supplying both carbon and nitrogen to these arid-land ecosystems. As such, they may represent an analog for soil development on the early Earth. BSCs occupy an extremely nutrient-poor niche, and meet their nutrient and metal requirements by manipulating their surroundings via the production of metal-binding ligands called siderophores. The soil crust’s metabolism affects the chemical composition of soil porewaters and soil solid phases; these alterations to soil metal contents may represent a biosignature for biological soil crusts that can be preserved over long time scales.

4 Institutions
3 Teams
1 Publication
1 Field Site
Field Sites

Project Progress

Biological soil crusts (BSCs) are consortium of cyanobacteria, algae, and fungi that play an important role in the primary development and maintenance of soil ecosystems across the globe, and may also have done so in early Earth history. Their success depends on the availability of nutrients, including trace metals required for enzymes that are involved in a range of metabolic processes including photosynthesis and nitrogen (N2) fixation. This project examines the mechanisms by which BSC obtain and utilize bioessential trace elements (especially Fe, and Mo). Using field-collected BSCs, we have demonstrated that nitrogen fixation by these communities are both N and Mo limited (paper in prep, Alexander). We also explored the effect that actively metabolizing BSCs have on soil solution metal concentrations. These results suggest that crust metabolism actively alters the surrounding soil chemistry (Alexander et al., in review) and lends support to the idea that BSCs may generate a discernible biosignature that can be preserved in soils. During the past year we have also successfully demonstrated that the BSC’s produce siderophores (metal binding ligands); that the dominant species present in crusts are not all siderophore producers; and we have identified nine novel siderophore producing organisms from the complex microbial consortium. This work resulted in an abstract for the 2011 AGU Fall meeting and a manuscript is in preparation.

    Hilairy Hartnett Hilairy Hartnett
    Ariel Anbar

    Ferran Garcia-Pichel

    Amisha Poret-Peterson

    Katie Alexander
    Graduate Student

    Objective 4.1
    Earth's early biosphere.

    Objective 5.3
    Biochemical adaptation to extreme environments

    Objective 6.1
    Effects of environmental changes on microbial ecosystems

    Objective 6.2
    Adaptation and evolution of life beyond Earth

    Objective 7.1
    Biosignatures to be sought in Solar System materials