F-54501 Vandewre-les-Nancy, and URA CNRS 1977, Ecologie Microbienne, USBSE,The taxonomic position of nitrogen-fixing strains that were isolated from rhizosphere macerates of rice cultivated in the Binh Thanh region of Vietnam was determined by using polyphasic taxonomy. We determined the phylogenetic relationships of these organisms by performing DNA-rRNA hybridization experiments with a labeled rRNA probe from the type strain of Burkholderia cepacia, and we found that they belong to a single rRNA complex. Other members of this rRNA complex were also studied, and the N,-fixing strains were found to be closely related to B. cepacia. In addition, all members of the rRNA complex containing B. cepacia were studied by performing auxanographic and DNA-DNA hybridization experiments. Phenotypically and genotypically, the N,-fixing isolates constitute a single cluster together with two strains of clinical origin. These organisms constitute a new Burkholderia species, for which the name Burkholderia vietnamiensis is proposed; the type strain of this species is TVV75 (= LMG 10929). All members of this species can fix nitrogen. On the basis of our polyphasic taxonomy results and previously published data we concluded that the genus Burkholderia should be restricted to the following species: B. cepacia (the type species), Burkholderia mallei, Burkholderia pseudomallei, B. vietnamiensis, Burkholderia gladioli, Burkholderia caryophylli, Burkholderia plantarii, Burkholderia glumue, Burkholderia vandii, BurkhoMeria cocovenenans comb. nov., and Burkholderia andropogonis comb. nov. On the basis of genotypic and phenotypic results [Alcaligenes] eutrophus, [BurkhoZderia] solanacearum, and[Burkholderia] pickettii belong to two other clusters whose internal structures must be studied further.On the basis of the results of extensive phenotypic studies and DNA-rRNA and DNA-DNA hybridization experiments performed by Palleroni, Stanier, and their collaborators, the genus Pseudomonas was divided into five groups (24, 43, 46, 56). Additional phylogenetic data have shown that these groups are only very remotely related and that each of them contains species belonging to other genera (21-23, 70, 71). In addition to the former pseudomonads that have been shown to belong to the genus Xanthomonas and to a smaller group related to Pseudomonas diminuta and Pseudomonas vesicularis (21-23,43) classified in the recently described genus Brevundirnonas (52), three large groups of pseudomonads can be considered. Pseudomonas rRNA group I (43) is part of rRNA superfamily I1 (18) or the gamma subclass of the Proteobacteria (S), where it constitutes a separate rRNA complex (18,21,22,68); this group represents the authentic pseudomonads which are grouped with Pseudomonas aeruginosa, the type species (43). Although the internal relationships within this group have not been determined yet, it is evident that the genus Pseudomonas must be limited to this group and that all other Pseudomonas species have been generically misnamed as determined by phylogenetic da...

Reasons are advanced for removal of Rhizobium ciceri, Rhizobium huakuii, Rhizobium loti, Rhizobium mediterraneum, and Rhizobium tianshanense from the genus Rhizobium and for establishment of Mesorhizobium gen. nov. for these species. A description of the genus Mesorhizobium and amended descriptions of Mesorhizobium ciceri, Mesorhizobium huakuii, Mesorhizobium loti, Mesorhizobium mediterraneum, and Mezorhizobium tianshanense are provided.In a review of root nodule symbioses by Vincent (22), the fast-growing rhizobia associated with Lotus comiculatus and Lupinus densiflorus were recognized as a separate group which merited a specific designation, and the name Rhizobium loti was tentatively proposed for it. Approval for the designation of R. loti as a new species was also voiced at a roundtable discussion on Rhizobium taxonomy associated with the 4th International Congress on Nitrogen Fixation at Canberra, Australia, in 1980. The subsequent publication of the new species in 1982 (9) enabled it to be included in a revised taxonomy of the Rhizobiaceae presented by Jordan in Bergey's Manual of Systematic Bacteriology (12).At that time R. loti was distinguished from other fast-growing rhizobia on the basis of flagellation (l), esterase patterns (14), response to isoflavonoids (18), plant nodulation (11, 12), internal antigens (23), electrophoresis of soluble cellular proteins (19,20), and DNA relatedness (4, 8). More recently, cellular fatty acid analysis was used to reveal differences, useful for identification purposes, between strains of R. loti and strains of the genus Agrobacterium and other Rhizobium or Sinorhizobium species (10). All of these methods differentiate species but give little indication of the relationships between species and genera.A n early indication of the relationship among R. loti, other Rhizobium species, and Sinorhizobium and Agrobacterium species was obtained by studying the intergeneric similarities of rRNA cistrons (7). The results of this analysis indicated that Rhizobium leguminosarum, Rhizobium galegae, Sinorhizobium meliloti, Sinorhizobium fredii, Agrobacterium tumefaciens (biovar l), and Agrobacterium rhizogenes (biovar 2) were all more closely related to one another than they were to R. loti. Subsequent analyses of 16s rRNA gene sequences of species in these genera have confirmed, refined, and extended this observation (21,24,25); the levels of 16s ribosomal DNA sequence similarity between R. loti and other Rhizobium and Agrobacterium species are around 93.5%. Consequently, there has been considerable support for the establishment of a separate genus for R. loti and related root nodule bacteria (5, 13, 27).The original description of R. loti (9) clearly indicated that fast-growing Lotus rhizobia formed part of an extensive plant cross-inoculation group involving plant species in the genera Lupinus, Ornithopus, Lotus, Anthyllis, Caragena, Astragalus, Ononis, Genista, and Mimosa. Jarvis et al. also indicated that the fast-growing Lotus rhizobia were related to rhizobia obtained from s...

The diversity among 43 isolates of the genus Frankia was studied by determining levels of deoxyribonucleic acid relatedness (S1 nuclease method) and DNA base compositions. The guanine + cytosine contents ranged from 66 to 75 mol% . At least nine genomic species were differentiated, including three genomic species among strains compatible with members of the genus Alnus, five genomic species among strains compatible with members of the family Elaeagnaceae, and one genomic species among strains compatible with members of the genus Casuan'na. Genomic species 1, which contained proposed type strain CpIl and nine strains that were compatible with members of the genus Ahus and were 64 to 97% related to strain ACoN24d, is Frankia alni. Four genomic species contained single strains that were 0 to 30% related to the other genomic species. Typical strains isolated from members of the genus Casuarina were found to be very homogeneous (69 to 100% related to strain ORS020606) and clearly separated from atypical strains. The nine genomic species delineated in this study cannot be named since no phenotypic tests are available for identification.