Expression by Soil Bacteria of Nodulation Genes from Rhizobium leguminosarum biovar trifolii

Abstract

Gram-negative, rod-shaped bacteria from the soil of white clover-ryegrass pastures were screened for their ability to nodulate white clover (Trifolium repens) cultivar Grasslands Huia and for DNA homology with genomic DNA from Rhizobium leguminosarum biovar trifolii ICMP2668 (NZP582). Of these strains, 3.2% were able to hybridize with strain ICMP2668 and nodulate white clover and approximately 19% hybridized but were unable to nodulate. Strains which nodulated but did not hybridize with strain ICMP2668 were not detected. DNA from R. leguminosarum biovar trifolii (strain PN165) cured of its symbiotic (Sym) plasmid and a specific nod probe were used to show that the relationship observed was usually due to chromosomal homology. Plasmid pPN1, a cointegrate of the broad-host-range plasmid R68.45 and a symbiotic plasmid pRtr5l4a, was transferred by conjugation to representative strains of nonnodulating, gram-negative, rod-shaped soil bacteria. Transconjugants which formed nodules were obtained from 6 of 18 (33%) strains whose DNA hybridized with that of PN165 and 1 of 9 (11%) strains containing DNA which did not hybridize with that of PN165. The presence and location of R68.45 and nod genes was confirmed in transconjugants from three of the strains which formed nodules. Similarly, a pLAFR1 cosmid containing nod genes from a derivative of R. leguminosarum biovar trifolii NZP514 formed nodules when transferred to soil bacteria. The genus Rhizobiuim is "characteristically able to invade

Relative genetic structure of a population of Rhizobium meliloti isolated directly from soil and from nodules of alfalfa (Medicago sativa) and sweet clover (Melilotus alba)

“…Several reports in which nonsymbiotic R. leguminosurum were qualitatively recovered directly from soils (Jarvis et al 1989; Soberon-Chavez h Najera 1989; Segovia et al 1991;Laguerre et af. 1993) have indicated that these bacteria may constitute a substantial fraction of field populations.…”

Determination of viability within serotypes of a soil population of Rhizobium leguminosarum bv. trifolii

“…In the pioneering studies of Bohlool and Schmidt (4), an indigenous soil-borne actinomycete was found to cross-react strongly with a fluorescent antibody to B. japonicum. More recently, nonnodulating bacteria that were either antigenically related or that showed partial DNA homology to symbiotically competent biovars of R. leguminosarum have been recovered directly from soil (21,43). Although the antiserum to serotype 36 of R. leguminosarum bv.…”

Genotypic diversity of Sinorhizobium (formerly Rhizobium) meliloti strains isolated directly from a soil and from nodules of alfalfa (Medicago sativa) grown in the same soil

“…All but one of the S. meliloti isolates from soil carried megaplasmids and all of them were able to nodulate and fix nitrogen in symbiosis with alfalfa, thus only symbiotic S. meliloti were isolated from soil. This result contrasts with the relatively large numbers of non‐symbiotic R. leguminosarum isolated from soils [14–17]. This may indicate that genes essential for the survival of S. meliloti in soils are located on the very large Sym megaplasmid and thus linked to symbiotic genes.…”

“…Methods have recently been developed to isolate Rhizobium and Bradyrhizobium strains directly from soil [14–19]. Symbiotic and non‐symbiotic Rhizobium leguminosarum were isolated directly from soils containing indigenous populations of this bacterium [14–17]. To our knowledge, there is only one report of direct isolation of S. meliloti from soil [20].…”