Location of genetic markers on the genome of Sinorhizobium meliloti strain 1021. Gene clusters located nearby each genetic marker are indicated by black boxes. It is noteworthy that the IGS
marker is located near genes involved in symbiotic specificity (nod genes), symbiotic efficiency (nif/fix genes), secretion (virB gene) and conjugation (tra genes). IGS
are located near genes involved in the synthesis of surface polysaccharides, which are also involved in the symbiotic interaction. IGS
is physically close to genes involved in secondary metabolic pathways.