Rhizobium loti, a New Species of Legume Root Nodule Bacteria

Abstract

Comparative studies of fast-growing Lotus rhizobia were reviewed, and as a result a new species, Rhizobium loti, is proposed. The type strain of this species, which was isolated from a root nodule on Lotus corniculatus (bird's-foot trefoil), is NZP 2213 (= ATCC 33669). Plant specificity, phage relationships, the solubleprotein pattern, and deoxyribonucleic acid base sequence homology distinguished R . loti from currently recognized Rhizobium species.Rhizobium species have been defined in terms of plant cross-inoculation groups (16). However, it is generally recognized that this approach is inadequate since cross-inoculation groups are not mutually exclusive (9, 11, 31) and plant specificity is probably a plasmid-borne character (4, 6, 21, 29). Furthermore, many of the strains studied have never been designated by a species name, including the Lotus rhizobia, which nodulate a variety of leguminous plants belonging to the genera Lupinus, Ornithopus, Anthyllis, Caragana, and Astragalus (13, 14).A revised classification of the genus (D. C. Jordan, personal communication) has been proposed for the forthcoming edition of Bergey ' s Manual of Determinative Bacteriology, in which the fast-growing species Rhizobium trifolii, Rhizobium phaseoli, and Rhizobium leguminosarum are combined as one species, designated R. leguminosarum (Frank) Frank, comprising three biovars (trifolii, phaseoli, and viceae). Rhizobium meliloti Dangeard is retained as a separate species in the genus Rhizobium, and those rhizobia which grow slowly on yeast extract media are transferred to a separate genus, Bradyrhizobium (15). Only one species is recognized in this genus, Bradyrhizobium japonicum (Kirchner) Jordan 1982. As part of this revision it is proposed that the fast-growing Lotus rhizobia and related strains be recognized as a new species, Rhizobium loti.Two groups of Lotus rhizobia have been recognized in comparative studies of bacteroid ultrastructure (7), internal antigens (23, 32), extracellular polysaccharide composition (2), enzymatic complement (17-19), gel electrophoresis of soluble proteins (27,28), growth rate and acid production on yeast extract media (1,5,20), susceptibility to flavolans and isoflavonoids (24, 25), susceptibility to antibiotics (22), phage relationships (26), deoxyribonucleic acid (DNA) homology (8, 12), and plant cross-nodulation (1, 8, 10, 13, 14, 22). Several of these criteria indicate that the fast-growing, acid-producing Lotus rhizobia are also clearly distinguishable from R. leguminosarum and R . meliloti (8,12,18,24,25, 28, 29, 32).Jensen and Hansen (13, 14) discovered an extensive cross-inoculation group involving the plant genera Lupinus, Ornithopus, Lotus, Anthyllis, Caragana, Astragalus, Ononis, Genista, and Mimosa, which were nodulated by both fast-and slow-growing rhizobia. Recent DNA-DNA hybridization studies have shown that fast-growing Lotus rhizobia are genetically related to rhizobia obtained from a variety of plant hosts, including Lotus corniculatus, Lotus divaricatus, Lotus maroccanus, Lotus...

Mesorhizobium chacoense sp. nov., a novel species that nodulates Prosopis alba in the Chaco Arido region (Argentina).

“…One of them, the genus Mesorhizobium (Jarvis et al, 1997), includes a group of species related to Mesorhizobium loti and obtained from a diverse range of host legumes including Lupinus, Ornithopus, Lotus, Anthillis, Caragena, Astragalus, Ononis, Genista, Mimosa, Cicer and Leucaena. At the time of description of the genus, it included the species Mesorhizobium ciceri (Nour et al, 1994), Mesorhizobium huakuii (Chen et al, 1991), M. loti (Jarvis et al, 1982), Mesorhizobium mediterraneum (Nour et al, 1995) and Mesorhizobium tianshanense (Chen et al, 1995 Mesorhizobium chacoense sp. nov.…”

Taxonomy of Bacteria Nodulating Legumes

“…31 This was the case of the species R. phaseoli and R. trifolii that were reclassified into R. leguminosarum and from this moment were considered by rhizobiologists as biovars from R. leguminosarum. Then, the genus Rhizobium contained only three species, the two old species R. leguminosarum and R. meliloti, and a new species named R. loti proposed by Jarvis et al 32 to include rhizobia nodulating legumes other than those nodulated by R. leguminosarum and R. meliloti. 31 It is necessary to take into account that in 1980 was published the valid list of bacterial species by Skerman et al 6 that included R. leguminosarum, R. phaseoli, R. trifolii and R. meliloti.…”

Nodule-Specific Regulation of Phosphatidylinositol Transfer Protein Expression in Lotus japonicus

“…Nodules, leaves, and stems of L. japonicus plants inoculated with Mezorhizobium loti strain NZP2235 (Jarvis et al, 1982) were harvested 35 days after inoculation; control uninoculated roots were collected from axenically grown L. japonicus plants of the same age. L. japonicus flowers were obtained from 2-to 3-month-old plants.…”