SINORHIZOBIUM MEDICAE SP-NOV, ISOLATED FROM ANNUAL MEDICAGO SPP

The taxonomic position of isolates of a new genomic species (designate d genomic species 2) obtained from several annual Medicago species aci d originating from different geographical locations was established th rough the results of phenotypic tests (including the results of auxano graphic and biochemical tests and symbiotic properties) and 16S rRNA p hylogenetic inferences. A comparison of the complete 16S rRNA sequence of a representative of genomic species 2 (strain A 321(T) [T = type s train]) with the 16S rRNA sequences of other members of the Rhizobiace ae and closely related taxa showed that genomic species 2 was phylogen etically related to Sinorhizobium meliloti, Sinorhizobium fredii, Sino rhizobium saheli, and Sinorhizobium teranga. The levels of sequence si milarity and observed numbers of nucleotide substitutions in Sinorhizo bium strains indicated that A 321(T) and S. meliloti exhibited the hig hest level of sequence similarity (99.7%), with four nucleotide substi tutions and one deletion. The results of a numerical analysis based on data from 63 auxanographic and biochemical tests clearly separated ge nomic species 2 isolates from S. meliloti. Genomic species 2 isolates nodulated and fixed nitrogen with Medicago polymorpha, whereas S. meli loti isolates were ineffective and formed rudimentary nodules on this host plant. On the basis of phenotypic and 16S sequence analysis data, genomic species 2 isolates cannot be assigned to a previously describ ed species. We propose that these isolates belong to a new species, Si norhizobium medicae.