SLOW-GROWING AND OLIGOTROPHIC SOIL BACTERIA PHYLOGENETICALLY CLOSE TOBRADYRHIZOBIUM-JAPONICUM

Eleven isolates of slow-growing oligotrophic bacteria from grassland s oil were found to be closely related by partial 16S rRNA sequence simi larity and many common taxonomic traits. Analysis of full 16S rRNA gen e sequences of four representative isolates and Agromonas oligotrophic a S58 indicated that they were more closely related to Bradyrhizobium japonicum, a symbiotic nitrogen-fixing bacterium, (similarity values: 98.1-98.8%) than other strains such as Bradyrhizobium elkanii, Nitroba cter spp., Rhodopseudomonas palustris, and Afipia spp. This result was supported by analysis of phenotypic traits and DNA-DNA hybridization analysis. No strain showed hybridization to nodD(1) YABC of B. japonic um, and only strain G14130 exhibited hybridization to nifDK- and hupSL -specific DNA. These latter genotypes are involved in the phenotypes o f nodulation and nitrogen fixation under microaerobic conditions. Thes e results suggest that the isolates possess a unique phylogenetic posi tion since they are closely related to B. japonicum though they do not have characteristics of symbiotic nitrogen fixation. (C) 1998 Federat ion of European Microbiological Societies. Published by Elsevier Scien ce B.V.