Plasmids with a Chromosome-Like Role in Rhizobia

摘要: Replicon architecture in bacteria is commonly comprised of one indispensable chromosome and several dispensable plasmids. This view has been enriched by the discovery additional chromosomes, identified mainly localization rRNA and/or tRNA genes, also experimental demonstration their requirement for cell growth. The genome Rhizobium etli CFN42 constituted six large plasmids, ranging size from 184 to 642 kb. Five plasmids are viability, but plasmid p42e unusually stable. One possibility explain this stability would be that genes on carry out essential functions, thus making it a candidate secondary chromosome. To ascertain this, we made an in-depth functional analysis p42e, employing bioinformatic tools, insertional mutagenesis, programmed deletions. Nearly 11% participate primary metabolism, involving biosynthetic functions (cobalamin, cardiolipin, cytochrome o, NAD, thiamine), degradation (asparagine melibiose), septum formation (minCDE). Synteny incompatibility studies revealed highly stable replicons equivalent content gene order other species. A systematic deletion allowed identification two (RHE_PE00001 RHE_PE00024), encoding, respectively, hypothetical protein with probable winged helix-turn-helix motif two-component sensor histidine kinase/response regulator hybrid protein, which growth rich medium. These data support proposal its homologous (pA, pRL11, pRLG202, pR132502) merit status chromosomes.