Arctic and subarctic soil populations of Rhizobium leguminosarum biovar trifolii nodulating three different clover species: Characterisation by diversity at chromosomal and symbiosis loci

Indigenous soil populations of Rhizobium leguminosarum biovar trifolii from Arctic and subarctic regions have been characterised with emphasis on chromosomal and symbiotic genes. Three clover species were used to trap rhizobia from soils along a latitudinal gradient from 78°N to 60°N in Norway. For the first time R. l. bv. trifolii was isolated from Svalbard at 78°N. Under the extreme conditions in the Arctic, rhizobia have survived as saprophytes and in symbiosis with clover legumes. The chromosomal diversity of the soil populations was mapped by rep-PCR. Separation of chromosomal types were strongly influenced by geographic origin. Symbiotic genes, the nodEF and nifDK IGS gene regions, were investigated by PCR-RFLP. The nifDK IGS were more conserved than the nodEF genes. Sym plasmids were widely distributed in different chromosomal types and across the latitudinal gradient.