"Adaptation of Frankia, alders, and their symbiosis to environmental stress. Adaptation au stress environnemental de Frankia, des aulnes et de leur symbiose."

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Filamentous actinobacteria of the genus Frankia are ubiquitous and participate significantly in global nitrogen fixation. With their host plants (actinorhizal plants, amongst which alders), they establish a root nodule symbiosis analogous to that of legumes with rhizobia. In North America, alders are of particular interest for their distribution, robustness and adaptation to a wide range of harsh environmental conditions. Although actinorhizal alders are routinely used for the revegetation of derelict lands, little research has focussed on how natural and anthropogenic stress (soil nutrient deficiency, heavy metals) affect the alder actinorhizal symbiosis. These questions are even more important considering that frankiae, in their saprophytic life cycle, are directly exposed to these stresses. Specifically, I will study: 1- cellular differentiation of growing Frankia spp. populations (i.e. massive conversion to difformed hyphae), 2- the study of interactions between alder, frankiae and ectomycorrhizal symbionts in soils that are contaminated with metals, and 3- the bacterial populations in root nodules. My research program focusses mainly on elucidating how actinorhizal alders and Frankia sp. adapt to environmental stress (both natural and anthropogenic). Through this knowledge, we are able to understand the impact of human activity on these organisms which are ubiquitous in Canada, and tailor rhizodegradation or phytoextraction technologies according to the natural potential of combinations of alder species and Frankia strains. It must be emphasized that the Frankia symbiosis (actinorhizal symbiosis) is relatively understudied. This contrasts with their importance in Nature; it is estimated that 15% to 25% of global nitrogen fixation can be attributed to these organisms. Unfortunately, the study of frankiae and their symbiosis to comprise a number of technical difficulties. I am addressing these difficulties using state-of-the-art techniques, in a systematic fashion, and pursuing this important research in an integrated manner. This results in the training of highly competent students, and in the involvement of industrial partners for the benefit of science and society.