Community Structure and Adaptive Strategies
of Fungi in Geothermal Soils

The Problem

Cluster of several plant species that thrive in geothermal soils - thermometer included.

There are approximately 500,000 abandoned mines in the western US. Collectively, these mines pollute rivers, streams, and western reservoirs with millions of tons of metals annually that degrade aquatic habitat and water used by humans for drinking, recreation, and irrigation. Unfortunately, the magnitude of this problem is such that physical corrective measures are very costly. However, there is great potential in decreasing or eliminating the flow of metals into aquatic ecosystems using biological communities to either accumulate or remediate metals from the abandoned mine tailings. Plant communities would be most desirable to accomplish this since they would act to control erosion as well as allow soil microbial communities and complex food webs to become established. The most likely places to identify potential organisms for this purpose are relatively extreme environments where organisms have had evolutionary time to adapt to abiotic stresses such as high metal concentrations.

Another component of this project is to understand how food webs decline after exposure to abiotic stresses and how food webs recover after restoration efforts are underway. Since food webs are critical to the health of ecosystems, this information will provide insight into optimizing habitat restoration strategies. In most habitats the connectivity between trophic levels is poorly understood as are the organismal changes that occur in soils impacted by stress. To study this we will incorporate new technology to detect and monitor specific microorganisms, assess soil chemistry in sites containing and devoid of plants/microbes, and assess potentially critical points of connectivity between trophic levels.

Objectives

Methodology

We began these studies on plants and fungi that thrive in the acidic geothermal soils in Yellowstone National Park. These soils contain high levels of metals deposited by acidified geothermal steam. We have isolated 20-30 different species of filamentous and single celled fungi in the soils and 2 filamentous fungi that are symbiotic with plants growing in the geothermal soils. The taxonomy and phylogeny of these fungi are currently being pursued using ribosomal sequence analysis. These

Setting up field experiment.

fungi will be cultured in medium containing high concentrations of different metals and then analyzed to determine the fate of the metals. This should reveal the mechanism(s) of metal tolerance (i.e. compartmentalization, exclusion, or conversion to less toxic forms). Once the mechanisms of metal tolerance are understood, the fungi will be incorporated into a series of experiments assessing metal stress on a variety of plant species. Similar experiments are being performed with the symbiotic fungi to determine if they confer metal, temperature, and acid tolerance to plants. During these studies it has become apparent that many of the fungi contain viral double stranded RNA molecules. We are characterizing the role that fungal viruses have in this plant community and if these molecules can be used to determine the relationships between fungi from different host plants and geographic locations. These experiments will allow us to identify combinations of fungi and plants that can be used to begin bioremediation studies in abandoned mine tailings throughout the western US. The potential for remediation is based on the fact that soil and symbiotic fungi require nutrients from plants to grow and most plant species are inhibited by metals. As the fungi grow, they will compartmentalize or convert metals creating a noninhibitory environment for the plants. As the community develops, a greater amount of metal can be accumulated or converted resulting in the decrease or elimination of stream contamination.

Highlights and Key Findings

High temperature exposure of Dichanthelium lanuginosum in the absence of its fungal symbiont - plants are dead.

This project has involved analysis of free living and symbiotic fungi, and the establishment of food webs. Free living fungi from geothermal soils have been isolated and analyzed. This work was compiled in a peer-reviewed publication in Applied and Environmental Microbiology. Several fungal symbionts have been isolated from plant species growing in the geothermal soils. We have isolated seeds from these plants and are able to grow them free of the symbionts. A recent manuscript in the journal Science describes field and laboratory experiments we performed indicating that the symbiotic fungi confer thermotolerance to the plants and are required for the survival of plants in geothermal soils. Currently, we are performing laboratory experiments that compare the ability of symbiotic and nonsymbiotic plants to tolerate heavy metals, drought, and salt In addition, we are screening these symbionts for host range and the ability to confer mutualistic benefits to other plant species. This year we will analyze several isolates of this symbiont from different plants in different geothermal locations for the distribution of fungal viruses and if those viruses impact symbioses or the ability of

High temperature exposure of Dichanthelium lanuginosum in the presence of its fungal symbiont - plants are alive.

free living fungi to survive abiotic stresses. We have recently been funded to begin studies on microbial food webs in extreme habitats. This year will begin studying the distribution of fungi identified as critical to the establishment and maintenance of food webs in the Dry Valley soil of the Antarctic. Several aspect of soil chemistry will be measured to correlate with microbial distribution patterns. In addition, new molecular targeting technology will be used to design probes to rapidly detect and quantify the occurrence of these organisms. Future projects will involve applying tools and information from this project to more complex aquatic systems such as riparian zones and estuaries.

Where Are We Headed In 2003

There are six plants species in the geothermal soils of Yellowstone national Park. Over the next year these plant species will be analyzed for fungal symbionts. Morphological and molecular studies will be performed to characterize the fungi and seeds will be collected from each plant for experimental studies. Plants will be cultivated in association or free of fungal symbionts so comparative studies may be performed. This will allow us to determine if the contribution of symbiosis to plant adaptation is common among different plant species in stressful habitats.

Thermal vent with a few plants (Dichanthelium lanuglinosum) below it.

After laboratory studies are completed, field experiments will be established to test the hypothesis that plants require fungal symbiosis to survive and adapt to stressful habitats.

Project Contact

Rusty Rodriguez
U.S. Geological Survey
Western Fisheries Research Center
6505 NE 65th St.
Seattle, WA 98115

Email: rusty_rodriguez@usgs.gov
Phone: 206-526-6282
Fax: 206-526-6654

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