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taiwanensis LMG19424 belongs to the rhizobia group of bacteria
and is therefore capable of establishing a nitrogen fixing symbiosis
with leguminous plants.
This symbiosis is established by the formation of specialized structures called nodules on the roots of the host plant, the interiors of which are where the bacteria fix nitrogen from the air. In the past, this symbiotic ability had been restricted to the alpha-proteobacteria, but recently this has been extended to a limited number of beta-proteobacteria belonging to the genera Burkholderia and Ralstonia.
R. taiwanensis LMG19424 was originally isolated from a nodule from the legume species Mimosa pudica in Taiwan. The genome of strain LMG19424 comprises of three replicons, a chromosome of 3.5 Mb, a megaplamid of 2.4 Mb and a symbiotic plasmid of 0.5 Mb which carries the genes that are essential for nodulation and nitrogen fixation.
Since R. taiwanensis LMG19424 is an atypical rhizobium and is phylogenetically distantly related to the classic rhizobia from the alpha-proteobacteria group, it will be important to compare the sequence from this genome with other rhizobia sequences (Sinorhizobium meliloti, Bradyrhizobium japonicum and Mesorhizobium loti). The sequence of R. taiwanensis will be extremely useful in the study of the origin, evolution and genetic basis of the rhizobium-legume symbiosis. It will also contribute to the understanding of the relationship between symbiosis and pathogenicity since the genus Ralstonia comprises of species that are plant pathogens, such as R. solanacearum, and opportunistic human pathogens.