RECLASSIFICATION OF AMERICAN RHIZOBIUM-LEGUMINOSARUM BIOVAR PHASEOLI TYPE-I STRAINS AS RHIZOBIUM-ETLI SP-NOV

A new Rhizobium species that nodulates Phaseolus vulgaris L. is propos ed on the basis of a sequence analysis of 16S ribosomal DNA. This taxo n, Rhizobium etli sp. nov., was previously named Rhizobium leguminosar um biovar phaseoli (type I strains) and is characterized by the capaci ty to establish an effective symbiosis with bean plants, the reiterati on of the nitrogenase structural genes, the organization of the common nodulation genes into two separate transcriptional units bearing nodA and nodBC, the presence of the polysaccharide inhibition gene, psi, a nd the 16S ribosomal DNA sequence. An analysis of the sequence of a fr agment of the 16S rRNA gene shows that this gene is quite different fr om the gene of R. leguminosarum. In addition, all R. etli strains have identical sequences. We describe these analyses and discuss additiona l evidence supporting our proposal.