Cryptic Plasmids of Alfalfa Root Nodule Bacteria Structural and Functional Diversity

Poster (download)

485

Alla Saksaganskaia¹, Viktoria Muntyan², Alexey Afonin³, Marina Roumiantseva^4
1ARRIAM, Saint-Petersburg, Pushkin, Russia, allasaksaganskaya@mail.ru
²ARRIAM, Saint-Petersburg, Pushkin, Russia, vucovar@yandex.ru
³ARRIAM, Saint-Petersburg, Pushkin, Russia, afoninalexeym@gmail.com
⁴ARRIAM, Saint-Petersburg, Pushkin, Russia, mroumiantseva@yandex.ru

Abundance of plasmids in genomes of root nodule nitrogen fixing bacteria (rhizobia) is their common feature. Plasmids harboring genes related to symbiosis are usually called symbiotic plasmids, while rhizobia can contain differing number of cryptic plasmids, which sizes are varied from 7 kbp to 600 kbp. Cryptic plasmids were predicted to be important both for the existence of rhizobia in soil and for formation of effective nitrogen-fixing symbiosis with particular host plant. Nevertheless, assemble and annotation of such replicons became possible only in the postgenomic era. In this work a structural and functional analysis of cryptic plasmids of Sinorhizobium meliloti which forming symbiosis with alfalfa was done. Native isolates of S. meliloti were recovered from nodules of alfalfa plants adapted to salinized soils at the Aral Sea region. The sequence analysis was done for four plasmids ranging in size from 31.2 kbp to 453.7 kbp. A large number of ORFs of cryptic plasmids of S. meliloti are associated with metabolic processes as it was established. For the first time prophage sequences were identified in cryptic plasmids. Data proving that cryptic plasmids of native strains are related to horizontal gene transfer and could be essential for rhizobia fitness.