Utilization of carbon and nitrogen compounds by Frankia in synthetic media and in root nodules of Alnus glutinosa, Hippophaë rhamnoides, and Datisca cannabina

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Abstract
Frankia AvcI1 utilizes only Tweens and fatty acids as sole carbon sources but N2, NH4+, NO3−, and various amino acids as nitrogen sources. The yield in propionate medium was increased by CO2. Cells grown in media with Tween 80 or acetate as C source contain the glyoxylate-cycle enzymes, isocitrate lyase and malate synthase. These enzymes are repressed in cells grown in media with propionate as well as in the symbiotic stage of Frankia in the nodules. The nature of the carbon compounds utilized by Frankia in the nodule symbiosis is discussed. Vesicle clusters derived from root nodules of Alnus respire succinate (however, only at a very low rate, which probably is due to damage of the membrane of the endophyte). Vesicle clusters derived from Alnus and Hippophaë nodules also take up O2 when supplied with a mixture of glutamate, malate, and NAD, indicating that the reduction equivalents could be transported from the host to the endophyte via the malate–aspartate shuttle. Vesicle clusters derived from Datisca respire succinate at a relatively high rate. Electron micrographs of Datisca nodules showed the presence of clusters of mitochondria embedded in the endophyte material, which might be of importance in the energy supply of the endophyte. These mitochondria are partly disintegrated during the preparation of the vesicle-cluster suspensions.

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