Life in soil by the actinorhizal root nodule endophyte Frankia. A review

Abstract

Frankia is a genus of soil actinomycetes famousfor its ability to form N2-fixing root nodule symbioses withactinorhizal plants. Although Frankia strains display a highdiversity in terms of ecological niches in soil, currentknowledge about Frankia is dominated by its life as anendophyte in root nodules. Increased use of molecularmethods has refined and expanded insights into endophytehostspecificities and Frankia phylogeny. This review hasfocus on Frankia as a soil organism, including its part ofmicrobial consortia, and how to study Frankia in soil. Wehighlight the use of nodulation tests and molecular methods toreveal population size and genetic diversity of Frankia in soiland discuss how autoregulation of nodulation and interactionswith other soil microorganisms may influence the results. Acomprehensive record of published interactions betweenFrankia and other soil microbes is summarized.