Some features of the DNA of Rhizobium bacteroids and bacteria

Sutton, W.D.

doi:10.1016/0005-2787(74)90312-8

Cited by 49 publications

(16 citation statements)

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“…In the last 20 years, several groups have suggested that during nodule development, the DNA of Rhizobium bacteroids is degraded, reduced in amount, or chemically modified (1, 3, 5, 7). Our own observations have not supported these suggestions: we found that several strains of Rhizobium bacteroids had amounts of DNA per cell equivalent to at least one complete bacterial chromosome, and that DNA isolated from purified bacteroids was similar to bacterial DNA in buoyant density, melting temperature, and kinetic complexity (9). Similar findings have recently been reported by Reijnders et al (8).…”

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Changes in the Number, Viability, and Amino-acid-incorporating Activity of Rhizobium Bacteroids during Lupin Nodule Development

Sutton¹,

Jepsen²,

Shaw³

1977

Plant Physiol.

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Between days 10 and 21 after inoculation of Lupinus angustdfolius seedlings with Rhizobium NZP 2257, the average nodule fresh weight increased 3-fold and the number of bacteroids per nodule increased more than 10-fold.The viability of Rhizobium bacteroids, as judged by their ability to form colonies on yeast-extract agar, declined from about 10% on days 10 and 11 after inoculation to about 0.3% on days 14 to 25. Bacteroid viabilty was highly sensitive to osmolarity.At optimal pH and K and Mg ion concentrations, the incorporation of 14C-glycine into isolated bacteroids was also very sensitive to osmolarity, and fell in parallel with bacteroid viability during nodule development.We suggest that at least two processes contribute to bacteroid nonviabilty: a reversible change in the ceUl wa stture occurring between days 10 and 14 after inoculation, and a subsequent irreversible change.The inability of Rhizobium bacteroids isolated from root nodules to divide on nutrient media, reported by Almon (2), has been confirmed (4) but not yet explained. Since nonviable differentiated forms of bacteria are very rare, it has been suggested that there may be some relationship between the inability of bacteroids to divide and the mechanisms whereby the plant controls bacteroid gene expression (9, 1 1). We are aware of only two sets of observations that may be relevant to this suggestion.a. In the last 20 years, several groups have suggested that during nodule development, the DNA of Rhizobium bacteroids is degraded, reduced in amount, or chemically modified (1, 3, 5, 7). Our own observations have not supported these suggestions: we found that several strains of Rhizobium bacteroids had amounts of DNA per cell equivalent to at least one complete bacterial chromosome, and that DNA isolated from purified bacteroids was similar to bacterial DNA in buoyant density, melting temperature, and kinetic complexity (9). Similar findings have recently been reported by Reijnders et al. (8). b. Rhizobium bacteroids have a low ratio of intact ribosomal RNA to DNA (11), suggesting that their capacity for protein synthesis may be restricted.Neither of these observations has been shown to bear any direct relationship to nonviability, and such questions as whether bacteroids are able to divide within the nodule at a time when they cannot divide on nutrient media, and whether nonviability develops before or after nitrogen-fixing ability seem to have been neglected.In this paper, we characterize the growth of bacteroid numbers and the development of nonviability in Rhizobium-infected lupin nodules, show that one cause of nonviability is the osmotic sensitivity of bacteroids, and explore the use of amino acid incorporation by bacteroids as a biochemical indicator for viability.MATERIALS AND METHODS Growth Conditions. Nodulated lupins (Lupinus angustifolius L. cv. Bitter Blue) were grown under controlled environment conditions (10), and Rhizobium strain NZP 2257 was cultured as previously described (9).Isolation of Bacteroids. Nodules were detac...

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“…Nodulated lupins (Lupinus angustifolius L. cv. Bitter Blue) were grown under controlled environment conditions (10), and Rhizobium strain NZP 2257 was cultured as previously described (9).…”

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confidence: 99%

Changes in the Number, Viability, and Amino-acid-incorporating Activity of Rhizobium Bacteroids during Lupin Nodule Development

Sutton¹,

Jepsen²,

Shaw³

1977

Plant Physiol.

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“…An alternative explanation for these observations may be based on the existence of plasmids in Rhizobittm (30,32,34,40). Evidence that plant specificity in Rhizobium is a plasmidborne character has accumulated over several years (5,11,18,30), and high-frequency transfer of nodulating ability from R. leguminosarum to R. trifolii, R. phaseoli, and a member of the cowpea miscellany has been demonstrated recently (21).…”

Section: Discussionmentioning

confidence: 99%

Deoxyribonucleic Acid Homology Among Strains of Rhizobium trifolii and Related Species

Jarvis

Dick

Greenwood³

1980

International Journal of Systematic Bacteriology

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Deoxyribonucleic acid homologies were determined among 27 strains of Rhizobium trifolii, 4 strains of Rhizobium leguminosarum, and 4 strains of Rhizobium phaseoli. Results from related strains indicated that deoxyribonucleic acid homologies correlate with serological relationships and that the ability to form nodules on legume roots can be lost without a detectable change in homology with an independent reference strain. All rhizobia which effectively nodulated Trifolium repens, Trifolium subterraneum, Trifolium ambiguum, and Vicia hirsuta formed one population with an average relatedness of 70% (range, 49 to 94%) and a ATm(e1 of 0.0 to 11.8OC with respect to reference strains capable of nodulating the first two clover species. Two strains from African Trifolium species and two strains from a northern Asiatic species were less closely related. The average relatedness of strains from Phaseolus vulgaris to clover rhizobia was 46% (range, 37 to 50%), and the ATm(e1 was 6.5 to ll.S0C. Taxonomic revisions consistent with these observations are discussed. It is proposed that R. trifolii and R. leguminosarum should be combined under the name which has priority, Rhizobium leguminosarum Frank. Within this species various biovars should be designated according to plant specificity. R. phaseoli should be retained at present as a separate species and examined in more detail. The results are discussed in relation to proposed genetic bases for plant specificity.The bacteria which form nodules on the roots of leguminous plants comprise the genus Rhizobium (22). Rhizobia have long been classified and named according to the specific plant or group of plants which they can nodulate (12,22). The plant hosts comprise a cross-inoculation group and harbor symbionts which nodulate only plants in the group. This classification is unsatisfactory for several reasons, Many legume hosts are not included in the six cross-inoculation groups which define the recognized species. Cross-inoculation groups are not mutually exclusive, and isolation of bacteria which nodulate plants in more than one group is a common event (10,39). Rhizobia readily lose their ability to effectively nodulate specific legumes (5, 23), and then their identity as rhizobia is dependent on knowledge of their earlier nodulating capability. Graham (16) has reviewed the limitations of the classification in Bergey's Manual of Determinative Bacteriology (22). Several groups have suggested that infectivity and effectiveness may be plasmid-borne characters (11,18,21,30), and it seems likely that this w i l l be demonstrated in the near future. Cross-inoculation groupings would then be untenable as a basis for classifying root nodule bacteria.Several alternative classifications have been proposed. Norris (27) examined 717 strains of 42 bacteria from 278 species of legumes and concluded that they could be classified into two groups: those which grew rapidly and formed acid on laboratory media and those which grew slowly and produced a neutral or alkaline reaction. Measurements of...

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“…Higashi (1967) was the first to suggest that host-range genes might be plasmidborne in Rhizobium and since that time many workers have shown that Rhizobium strains carry plasmids (Sutton, 1974;Nuti et al, 1977;C a s e et al, 1979). Dunican and co-workers have reported that nitrogen-fixation (Nif) genes are likely to be plasmid-borne and are transmissible to Klebsiella (Dunican et al, 1976;Stanley & Dunican, 1979).…”

Section: Early Genetic Studies (1941-1970)mentioning

confidence: 99%

The Development of Rhizobium Genetics: The Fourth Fleming Lecture

Beringer

1980

Microbiology

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The rhizobia are Gram-negative bacteria of major agricultural importance because of their ability to form nitrogen-fixing nodules on the roots of leguminous plants. The nitrogen fixation genes are carried by the rhizobia and are possibly only expressed in nature within the root nodule. Usually a given strain of Rhizobium can nodulate only a limited number of legume species. For temperate species this has given rise to a taxonomic classification based on the range of host plants that are nodulated. For example, Rhizobium trifolii includes those rhizobia which (ideally) nodulate only clovers (Trifolium spp.) which, in turn, are (ideally) nodulated only by strains of R. trfolii. However, while this grouping works reasonably well with temperate legumes, the far more numerous tropical legumes and rhizobia appear not to show the same host-Rhizobium specificity. A more useful characterization is on the basis of growth rate which reflects basic metabolic differences : temperate rhizobia on the whole are fast growers (taking 3 to 7d to form colonies on agar plates) while the others are generally slow growers (7 to 21 d).Root nodules are formed as the result of a series of poorly understood interactions between the appropriate Rhizobium species and its host plant. There is evidence that the population of rhizobia in the soil is stimulated by legumes (Robinson, 1967) but insufficient data are available to determine whether this is specific for a given host-Rhizobium combination, or is a general response of rhizobia to the presence of leguminous plants. Recognition, which may involve lectin binding (Dazzo & Hubbell, 1975), probably occurs before entry into the root, usually through root hairs or, more rarely, through breaks in the root occurring, for example, at the emergence of lateral roots. Within root hairs the bacteria are always enclosed within a tube, the infection thread, which is surrounded by a pectic and cellulose wall material that is continuous with the plant cell wall. The infection thread branches and penetrates through cells within the cortex. This growth is correlated with (stimulates?) cell division in the inner root cortex and the growth of the root nodule. Nodule formation, unlike tumour formation by Agrobacterium tumefaciens (another member of the Rhizobiaceae), is controlled, and a differentiated structure is formed.Within the nodule the rhizobia differentiate into bacteroids, which are the nitrogen-fixing forms. The plant produces globin (Sidloi-Lumbroso et al., 1978); this combines with haem produced by the rhizobia (Cutting & Schulman, 1969) to form leghaemoglobin, which appears to be a prerequisite for a nitrogen-fixing legume nodule. Once infection has occurred the plant provides the rhizobia with all their nutrient requirements and, in turn, receives fixed nitrogen when a nitrogen-fixing strain of Rhizobium is involved.We know that rhizobia can produce indole-acetic acid (Dullaart, 1970) and very small amounts of cytokinins (Phillips & Torrey, 1972), both of which are important plant hormones. ...

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Some features of the DNA of Rhizobium bacteroids and bacteria

Cited by 49 publications

References 30 publications

Changes in the Number, Viability, and Amino-acid-incorporating Activity of Rhizobium Bacteroids during Lupin Nodule Development

Changes in the Number, Viability, and Amino-acid-incorporating Activity of Rhizobium Bacteroids during Lupin Nodule Development

Deoxyribonucleic Acid Homology Among Strains of Rhizobium trifolii and Related Species

The Development of Rhizobium Genetics: The Fourth Fleming Lecture

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