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Phylogenetic relationships and host range of Rhizobium spp. that nodulate Phaseolus vulgaris L.

ABSTRACT: We determined the nucleotide sequences of 16S rRNA gene segments from five Rhizobium strains that have been isolated from tropical legume species. All share the capacity to nodulate Phaseolus vulgaris L., the common bean. Phylogenetic analysis confirmed that these strains are of two different chromosomal lineages. We defined the host ranges of two strains of Rhizobium etli and three strains of R. tropici, comparing them with those of the two most divergently related new strains. Twenty-two of the 43 tested legume species were nodulated by three or more of these strains. All seven strains have broad host ranges that include woody species such as Albizia lebbeck, Gliricidia maculata, and Leucaena leucocephala.

SUBMITTER: Hernandez-Lucas I

PROVIDER: S-EPMC167551 | biostudies-other | 1995 Jul

REPOSITORIES: biostudies-other

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Phylogenetic relationships and host range of Rhizobium spp. that nodulate Phaseolus vulgaris L.

Hernandez-Lucas I I Segovia L L Martinez-Romero E E Pueppke S G SG

Applied and environmental microbiology 19950701 7

We determined the nucleotide sequences of 16S rRNA gene segments from five Rhizobium strains that have been isolated from tropical legume species. All share the capacity to nodulate Phaseolus vulgaris L., the common bean. Phylogenetic analysis confirmed that these strains are of two different chromosomal lineages. We defined the host ranges of two strains of Rhizobium etli and three strains of R. tropici, comparing them with those of the two most divergently related new strains. Twenty-two of th ...[more]

PMID: 7618891

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Project description:BackgroundRhizobium tropici CIAT 899 and Rhizobium sp. PRF 81 are α-Proteobacteria that establish nitrogen-fixing symbioses with a range of legume hosts. These strains are broadly used in commercial inoculants for application to common bean (Phaseolus vulgaris) in South America and Africa. Both strains display intrinsic resistance to several abiotic stressful conditions such as low soil pH and high temperatures, which are common in tropical environments, and to several antimicrobials, including pesticides. The genetic determinants of these interesting characteristics remain largely unknown.ResultsGenome sequencing revealed that CIAT 899 and PRF 81 share a highly-conserved symbiotic plasmid (pSym) that is present also in Rhizobium leucaenae CFN 299, a rhizobium displaying a similar host range. This pSym seems to have arisen by a co-integration event between two replicons. Remarkably, three distinct nodA genes were found in the pSym, a characteristic that may contribute to the broad host range of these rhizobia. Genes for biosynthesis and modulation of plant-hormone levels were also identified in the pSym. Analysis of genes involved in stress response showed that CIAT 899 and PRF 81 are well equipped to cope with low pH, high temperatures and also with oxidative and osmotic stresses. Interestingly, the genomes of CIAT 899 and PRF 81 had large numbers of genes encoding drug-efflux systems, which may explain their high resistance to antimicrobials. Genome analysis also revealed a wide array of traits that may allow these strains to be successful rhizosphere colonizers, including surface polysaccharides, uptake transporters and catabolic enzymes for nutrients, diverse iron-acquisition systems, cell wall-degrading enzymes, type I and IV pili, and novel T1SS and T5SS secreted adhesins.ConclusionsAvailability of the complete genome sequences of CIAT 899 and PRF 81 may be exploited in further efforts to understand the interaction of tropical rhizobia with common bean and other legume hosts.

Project description:We studied symbiotic performance of factorial combinations of diverse rhizobial genotypes (GR) and East African common bean varieties (GL) that comprise Andean and Mesoamerican genetic groups. An initial wide screening in modified Leonard jars (LJ) was followed by evaluation of a subset of strains and genotypes in pots (contained the same, sterile medium) in which fixed nitrogen was also quantified. An additive main effect and multiplicative interaction (AMMI) model was used to identify the contribution of individual strains and plant genotypes to the GL × GR interaction. Strong and highly significant GL × GR interaction was found in the LJ experiment but with little evidence of a relation to genetic background or growth habits. The interaction was much weaker in the pot experiment, with all bean genotypes and Rhizobium strains having relatively stable performance. We found that R. etli strain CFN42 and R. tropici strains CIAT899 and NAK91 were effective across bean genotypes but with the latter showing evidence of positive interaction with two specific bean genotypes. This suggests that selection of bean varieties based on their response to inoculation is possible. On the other hand, we show that symbiotic performance is not predicted by any a priori grouping, limiting the scope for more general recommendations. The fact that the strength and pattern of GL × GR depended on growing conditions provides an important cautionary message for future studies.IMPORTANCE The existence of genotype-by-strain (GL × GR) interaction has implications for the expected stability of performance of legume inoculants and could represent both challenges and opportunities for improvement of nitrogen fixation. We find that significant genotype-by-strain interaction exists in common bean (Phaseolus vulgaris L.) but that the strength and direction of this interaction depends on the growing environment used to evaluate biomass. Strong genotype and strain main effects, combined with a lack of predictable patterns in GL × GR, suggests that at best individual bean genotypes and strains can be selected for superior additive performance. The observation that the screening environment may affect experimental outcome of GL × GR means that identified patterns should be corroborated under more realistic conditions.

Dataset Information

Phylogenetic relationships and host range of Rhizobium spp. that nodulate Phaseolus vulgaris L.

Publications

Phylogenetic relationships and host range of Rhizobium spp. that nodulate Phaseolus vulgaris L.

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