INTERNATIONALJOURNAL OF SYSTEMATICBACTERIOLOGY, July 1982, p. 378-380 Vol. 32, No. 3 OO20-7713/82/030378-03$02 .OO/O Rhizobiurn loti, a New Species of Legume Root Nodule Bacteria B. D. W. JARVIS,' C. E. PANKHURST,' AND J. J. PATEL' Department of Microbiology and Genetics, Massey University, and Applied Biochemistry Division, Department of Scientific and Industrial Research,' Palmerston North, New Zealand 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 soluble- protein pattern, and deoxyribonucleic acid base sequence homology distinguished R. loti from currently recognized Rhizobium species. Rhizobium species have been defined in terms 10, 13, 14, 22). Several of these criteria indicate of plant cross-inoculation groups (16). However, that the fast-growing, acid-producing Lotus rhi- it is generally recognized that this approach is zobia are also clearly distinguishable from R. inadequate since cross-inoculation groups are leguminosarum and R. meliloti (8,12,18,24,25, not mutually exclusive (9, 11, 31) and plant 28, 29, 32). specificity is probably a plasmid-borne character Jensen and Hansen (13, 14) discovered an (4, 6, 21, 29). Furthermore, many of the strains extensive cross-inoculation group involving the studied have never been designated by a species plant genera Lupinus, Ornithopus, Lotus, An- name, including the Lotus rhizobia, which nodu- thyllis, Caragana, Astragalus, Ononis, Genista, late a variety of leguminous plants belonging to and Mimosa, which were nodulated by both the genera Lupinus, Ornithopus, Anthyllis, Car- fast- and slow-growing rhizobia. Recent DNA- agana, and Astragalus (13, 14). DNA hybridization studies have shown that A revised classification of the genus (D. C. fast-growing Lotus rhizobia are genetically relat- Jordan, personal communication) has been pro- ed to rhizobia obtained from a variety of plant posed for the forthcoming edition of Bergey 's hosts, including Lotus corniculatus, Lotus di- Manual of Determinative Bacteriology, in which varicatus, Lotus maroccanus, Lotus tenuis, the fast-growing species Rhizobium trifolii, Rhi- Caragana arborescens, Cicer arietinum, Lue- zobium phaseoli, and Rhizobium legumino- caena leucocephala, Lupinus densiflorus, Ono- sarum are combined as one species, designated brychis viciifolia, Parochetus communis, Psora- R. leguminosarum (Frank) Frank, comprising lea eriatha, Robinia pseudoacacia, Sophora three biovars (trifolii, phaseoli, and viceae). angustifolia, Sophora microphylla, Sophora te- Rhizobium meliloti Dangeard is retained as a traptera, and Trifolium lupinaster (8), as well as separate species in the genus Rhizobium, and Carmichaelia species (12). Consequently, we those rhizobia which grow slowly on yeast ex- expect that although the description of R. loti tract media are transferred to a separate genus, given below is based on characteristics of well- Bradyrhizobium (15). Only one species is recog- studied root nodule bacteria (Table 1) from nized in this genus, Bradyrhizobium japonicum Lotus corniculatus and Lotus tenuis, the de- (Kirchner) Jordan 1982. As part of this revision scription probably applies to rhizobia from the it is proposed that the fast-growing Lotus rhizo- wider range of plant species indicated above. bia and related strains be recognized as a new Rhizobium loti sp. nov. (M.L. noun Lotus species, Rhizobium loti. generic name; M.L. gen. noun loti of Lotus). Two groups of Lotus rhizobia have been rec- Short, gram-negative, nonsporeforming rods ognized in comparative studies of bacteroid which are motile predominantly by means of one ultrastructure (7), internal antigens (23, 32), polar or subpolar flagellum. In nodules the cells extracellular polysaccharide composition (2), are bacteroids (i.e., club shaped and branched) enzymatic complement (17-19), gel electropho- and contain inclusion bodies composed of poly- resis of soluble proteins (27,28), growth rate and p-hydroxybutyric acid. Other inclusions, such acid production on yeast extract media (1,5,20), as polyphosphate bodies, glycogen granules, susceptibility to flavolans and isoflavonoids (24, and lipid droplets, are not present. 25), susceptibility to antibiotics (22), phage rela- Colonies on Vincent yeast mannitol agar (30) tionships (26), deoxyribonucleic acid (DNA) ho- are more than 1 .O mm in diameter after 7 days at mology (8, 12), and plant cross-nodulation (1, 8, 28"C, but growth is inhibited at 42°C. Growth at 378 VOL. 32, 1982 NOTES 379 TABLE 1. Fast-growing Lotus rhizobia included as members of R. loti and references in which these strains are described Strain" Reference(s) Other sources of informat ionb NZP 2014 2, 7, 23, 26 Patel; Pankhurst NZP 2024 2, 7, 23 Pankhurst NZP 2034 2, 8, 23 NZP 2037 2, 7, 8, 22, 23, 26 Patel; Pankhurst NZP 2042 2, 7, 23 Patel NZP 2048 2, 7, 22, 23 Patel NZP 2079 2, 23 Pankhurst NZP 2985 2, 7, 23 NZP 2150 2, 7, 23 Pankhurst NZP 2171 2, 7, 23 NZP 2196 (= SU343) 2, 7, 8, 23 Patel NZP 2205 7, 23, 26 Patel NZP 2213 7, 8, 22, 23, 26 Patel; Pankhurst NZP 2227 (= strain 461, 7, 8, 23, 26 Patel University of Guelph) NZP 2230 (= CC809a) 2, 8, 23 NZP 2234 (= CC811) 2, 7, 23 NZP 2235 (= CC812a) 23 Patel NZP 2238 (= Lc265Da) 7, 8, 22, 23, 26 Patel NZP 2260 8, 23, 26 Patel a NZP, New Zealand Department of Scientific and Industrial Research, Applied Biochemistry Division. Patel, J. J. Patel (unpublished data from a survey of bacteriophage host specificity involving five phage races and 270 Rhizobium strains); Pankhurst, C. D. Pankhurst, unpublished data on the responses of 24 Rhizobium strains in 28 physiological tests. 28°C on yeast mannitol agar is inhibited by 3% Rhizobium sp. strain CC811 from Lotus cornicu- NaCl and by pH values of less than 4.0 or more latus (46 to 74%; mean, a%),and Rhizobium than 10.0. On Vincent medium without manni- sp. strain CC809a from Lotus maroccanus (32 to tol, all strains utilize one or more of the follow- 59%; mean, 47%) indicate that R. loti can be ing carbohydrates and form acidic end products: clearly distinguished from other fast-growing glucose, galactose, fructose, arabinose, xylose, rhizobia. Strains of rhizobia from a variety of rhamnose, maltose, sucrose, lactose, trehalose, other plants have similar genetic relationships, raflinose, mannitol, and dulcitol. indicating that R. loti forms part of a larger The electrophoretic patterns of the soluble group of root nodule bacteria. proteins from strains of fast-growing Lotus rhi- Nitrogen-fixing (effective) nodules are nor- zobia are similar to one another and are distin- mally formed on the roots of Lotus corniculatus guishable from those of other species of fast- (bird's-foot trefoil), Lotus tenuis (slender bird's- growing rhizobia. foot trefoil), Lupinus densgorus (lupine), and All strains produce extracellular polysaccha- Anthyllis vulneraria (kidney vetch). A few rides which contain uronic acid, galactose, and strains nodulate effectively on Lotus peduncula- glucose. Somatic antigens are highly strain spe- tus (Lotus uliginosus; big trefoil) or Leucaena cific, but internal antigens show a reaction of leucocephala. Ineffective nodules may be identity between strains and can be used to formed on Lotus pedunculatus (Lotus uligino- distinguish R. loti from slow-growing Lotus rhi- sus), Lotus angustissimus (narrow-leaved Lo- zobia and from other Rhizobium nomenspecies. tus), Leucaena leucocephala, Clianthus puni- Cells can be infected by bacteriophages be- cens (red kowhai), Acacia sophorea (Acacia longing to Bradley morphological types B and C longifolia ; sallow wattle), Carmichaelia angus- (3). These phages are host range specific, and tata (large-flowered broom), Phaseolus vulgaris susceptibility to 4203711 may be used to distin- (kidney bean), Macroptilium atropurpureum guish R. loti from slow-growing Lotus rhizobia (siratro), and Ornithopus sativus (serradella). and from other Rhizobium nomenspecies. The type strain of R. loti is NZP 2213, a The guanine-plus-cytosine content of the culture of which has been deposited in the DNA of R. loti is 59 to 64 mol%. DNA-DNA American Type Culture Collection under the hybridizations with reference DNAs from R. number ATCC 33669. This strain conforms to trifolii strain CC275e (5 to 13%; mean, 8%), R. the description given above for the species with meliloti strain SU47 (5 to 15%; mean, lo%), respect to morphology, physiology, antigenic 380 NOTES INT. J. SYST.BACTERIOL. relationships, and plant specificity. It is lysed by 13. Jensen, H. L. 1967. Mutual host plant relationships in two groups of legume root nodule bacteria (Rhizobium spp.). bacteriophages 1through 7 of the 2037 series and Arch. Microbiol. 59:174-179. by +2205 but not by any bacteriophage from 14. Jensen, H. L., and A. L. Hansen. 1968. Observations on slow-growing Lotus rhizobia (26). The percent host plant relations in root nodule bacteria of the Lotus- DNA-DNA homologies with R. trifolii CC275e, Anthyllis and Lupinus-Ornithopus groups. Acta Agric. Scand. 18:135-142. R. meliloti SU47, R. loti CC811, and R. loti 15. Jordan, D. C. 1982. Transfer of Rhizobium japonicum CC809a are 10, 5, 60, and 47%, respectively. Buchanan 1980 to Bradyrhizobium gen. nov., a genus of Nitrogen-fixing nodules are formed on the roots slow-growing, root nodule bacteria from leguminous of the following plants: Lotus corniculatus, Lo- plants. Int. J. Syst. Bacteriol. 32:136-139. tus tenuis, Lotus japonicus, Lotus krylovii, Lo- 16. Jordan, D. C., and 0. N. Allen. 1974. Family 111. Rhizo- biaceae Conn, 1938, p. 261-264. In R. E. Buchanan and tus j?licalius, and Lotus schoelleri. Nodules N. E. Gibbons (ed.), Bergey’s manual of determinative which cannot fix nitrogen are formed on Lotus bacteriology, 8th ed. The Williams & Wilkins Co., Balti- pedunculatus, Lotus hispidus (Lotus suave- more. dens), Lotus angustissimus. 17. Martinez-de Drets, G., and A.