Size and Diversity of Frankia Populations in Soil

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Frankia are N2-fixing, sporulating, gram positive, filamentous bacteria (Actinomycetales) capable of forming root nodules on a variety of predominantly woody perennial plants, including Alnus and Ceanothus. These actinorhizal associations contribute significant quantities of nitrogen (50-150 Kg N ha-1 ya-1) to temperate forest ecosystems. In addition to enhancing forest productivity via nitrogen fixation, some actinorhizal plants, such as Alnus rubra in the Pacific Northwest, are important timber resources. Ecological studies of Frankia in soil are in their infancy, primarily because of the difficulty of isolating Frankia from soil and of differentiating Frankia strains from each other and from other soil microorganisms. No Frankia have been isolated from Ceanothus, a plant important to forest productivity in Oregon. Even alder, from which the majority of strains have been isolated, harbors many strains which cannot be cultured at this time. In order to assess the diversity of Frankia in soil, it is necessary to develop efficient methods of DNA extraction and a means of distinguishing among Frankia strains. This research will quantify and potentially improve soil DNA extraction efficiency. It will also develop a means of differentiating among Alnus-infective Frankia strains based on differences in the DNA sequence of rrn gene.