Multiple gene genealogical analyses reveal both common and distinct population genetic patterns among replicons in the nitrogen-fixing bacterium Sinorhizobium meliloti

Sinorhizobium meliloti is a Gram-negative alpha-proteobacterium that can form symbiotic relationships with alfalfa and fix atmospheric nitrogen. The complete genome of a laboratory strain, Rm1021, was published in 2001, and the genome of this strain is arranged in three replicons: a chromosome of 3.65 million base pairs (Mb), and two megaplasmids, pSymA (1.35 Mb) and pSymB (1.68 Mb). However, the potential difference in genetic variation among …