NITROGEN FIXATION.Nitrogen-fixing BACTERIA and microorganisms are capable of TRANSFORMING atmospheric nitrogen into fixed nitrogen.Symbiotic nitrogen fixation is a mutualistic relationship in which plants provide a niche and fixed carbon to bacteria in exchange for fixed nitrogen.an example for Symbiotic nitrogen fixation is the symbiosis between actinorhizal trees and shrubs, such as Alder with the actinomycete FrankiaThe nonsymbiotic bacteria include the cyanobacteria or blue-green algae Anabaena and Nostoc and Azotobacter, Beijerinckia, and Clostridium. Biological nitrogen fixation was discovered by Beijerinck in 1901 and is carried out by a specialized group of prokaryotes. Pullularia is a genus of fungi, forming yeast-like colonies that cause discoloration of pulp and paper. Chlorobium is a symbiotic green sulfur bacterium isolated from the phototrophic CONSORTIUM Chlorochromatium aggregatum.