[Show abstract][Hide abstract] ABSTRACT: Among the leguminous trees native to Uruguay, Parapiptadenia rigida (Angico), a Mimosoideae legume, is one of the most promising species for agroforestry. Like many other legumes, it is able to establish symbiotic associations with rhizobia and belongs to the group known as nitrogen-fixing trees, which are major components of agroforestry systems. Information about rhizobial symbionts for this genus is scarce, and thus, the aim of this work was to identify and characterize rhizobia associated with P. rigida. A collection of Angico-nodulating isolates was obtained, and 47 isolates were selected for genetic studies. According to enterobacterial repetitive intergenic consensus PCR patterns and restriction fragment length polymorphism analysis of their nifH and 16S rRNA genes, the isolates could be grouped into seven genotypes, including the genera Burkholderia, Cupriavidus, and Rhizobium, among which the Burkholderia genotypes were the predominant group. Phylogenetic studies of nifH, nodA, and nodC sequences from the Burkholderia and the Cupriavidus isolates indicated a close relationship of these genes with those from betaproteobacterial rhizobia (beta-rhizobia) rather than from alphaproteobacterial rhizobia (alpha-rhizobia). In addition, nodulation assays with representative isolates showed that while the Cupriavidus isolates were able to effectively nodulate Mimosa pudica, the Burkholderia isolates produced white and ineffective nodules on this host.
Applied and Environmental Microbiology 03/2012; 78(6):1692-700. · 3.95 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Commercial forest plantations have increased during the last decade in Uruguay in soils of low cropping capability. Eucalyptus grandis (Hill ex Maiden) has been the main species planted due to its fast growth and adaptability to climate fluctuations. Assuming that the conversion from natural grazed pastures to commercial Eucalyptus plantations generates significant changes in the soil biological properties, we compared microbial enumeration and variables directly related to microbial activity to characterize these changes, as well as to determine the extent to which these soil biological properties change seasonally and with soil depth. The soil use conversion from pasture to forest land did not have a significant effect on the number of cellulolytic aerobes, P-solubilizers and Azotobacter spp. communities. Soil respiration, the C-mineralization coefficient, dehydrogenase, fluorescein diacetate hydrolysis and acid and alkaline phosphatase activities were affected significantly. Microbial enumeration of cellulolytics, P-solubilizers and Azotobacter spp., and parameters related to microbial biomass, soil respiration and the C-mineralization coefficient showed marked effects of sampling season. This, however, was not the case for the relative levels of the enzyme activities evaluated. These results indicated that the enzyme activities evaluated were sensitive and reliable indicators of the biochemical changes generated by the soil use change. Spring appeared to be a better time for sampling than summer or winter because enzyme activities tended to be higher. Soil sampling depth was shown to be an important factor for obtaining consistent results, especially for the measurement of enzyme activities. For the last indicators, as well as the others, better results were obtained sampling and analyzing the upper 10 cm of the mineral soil profile. Our work suggested that microbial biomass, soil respiration, and enzyme activities are useful tools to assess biological soil quality changes due to the conversion of pasture land to planted E. grandis forest.
[Show abstract][Hide abstract] ABSTRACT: Legume trees are symbiotically associated with rhizobia and mycorrhizal fungi, microorganisms that improve their growth. The objective of this work was to characterize 61 rhizobial isolates from eight species of native legume trees: Acacia caven, Inga urugüensis, Lonchocarpus nitidus, Prosopis nigra, Sesbania virgata, Peltophorum dubium, Enterolobium contortisiliquum and Erythrina crista-galli. The strains were isolated from nodules with high nitrogenase activity and their growth rate, antibiotic, salinity and acidity resistances were determined. Their relationships were analyzed building a matrix with the resistance characteristics. Most of the isolates were fast growers and acid-producing with high level of exopolysaccharides. In general, isolates were erythromycin resistant but sensitive to rifampicin. All the isolates grew well at pH 5.5 while 75% did so at pH 4.4. More than 60% of the isolates grew in 2% of NaCl but this declined to 21% of the isolates in 3% NaCl. This population showed high antibiotic, salinity and pH resistance, suggesting adaptability to major ecological environment stresses, and great saprohytic competence within soil environments. Isolates from the same host showed high homology between them.
[Show abstract][Hide abstract] ABSTRACT: The leguminous Acacia caven, Erythrina crista-galli, Enterolobium contortisiliquum, Prosopis affinis and P. nigra nodulated with rhizobial strains isolated from other legume trees; therefore they were considered to be promiscuous (poorly specific) for nodulation. Sesbania punicea and Parapiptadenia rigida did not nodulate with the different strains, indicating a significant specificity for nodulation. A. caven was promiscuous for nodulation and nodulated with both fast- and slow-growing strains of rhizobia and our data suggest that the most efficient strains would be fast-growing rhizobia. A. caven was specific for effectivity since the amount of N2 which was fixed markedly depended on the strain. The relative efficiency (RE) of 6 out of the 11 strains used was higher than 0.80, suggesting they had an active uptake hydrogenase. Ac5, a strain isolated from A. caven, exhibited the highest N2-fixing ability and highest NE (nodule efficiency) when inoculated on its host and also had the highest RE. Shoot dry weight and acetylene reducing activity (ARA) were significantly correlated with the amount of N2 fixed (determined by the total nitrogen difference method), indicating that any of these methods could be used for screening the strains according to their ability to fix N2. The relative efficiency was not correlated with any of these parameters.
[Show abstract][Hide abstract] ABSTRACT: A survey of the nodulating ability of 17 Uruguayan native and subspontaneous tree legumes has added Inga uragüensis to the list of legumes known to fix N2. Nodulation and N2 fixation capability of the following species were confirmed: Acacia caven, Calliandra tweediei, Parapiptadenia rigida, Lonchocarpus nitidus, Erythrina crista-galli. Whereas A. caven bore many nodules in all soil types observed, Prosopis nigra and P. affinis were always poorly nodulated. Seedlings of E. crista-galli bore aerial nodules at the base of their stem when grown in waterlogged conditions. The morphology, structure and nitrogenase activity (ARA) of the aerial nodules were similar to root nodules. Nodulation ability of Geoffroea decorticans was not confirmed. The species belonging to the Caesalpinoideae sub-family did not nodulate and were unable to do so even when they were inoculated with a mixture of rhizobia strains, thus confirming previous observations. Nodule morphology was described according to Corby's classification. Anatomical studies showed the presence of spaces in the inner zone of A. caven nodules. E. crista-galli and Enterolobium contortisiliquum nodules exhibited several infected zones, probably related to the coralloid morphology of the nodules. The acetylene-reducing activity of the nodules of the different species was generally low. Rhizobial strains were isolated from the most active nodules for future investigations.
[Show abstract][Hide abstract] ABSTRACT: This report describes some biochemical and genetic characteristics of seven rhizobial isolates that nodulate legume trees Inga uragüensis, Prosopis nigra, Acacia caven, Erythrina crista-galli and Enterolobium contortisiliquum, native to Uruguay. Based on specific growth rates, carbon source utilization and acid production the isolates could be assigned to the fast-growing group of rhizobia. The analysis of plasmid content showed that from seven isolates examined, three contained a single plasmid of approximately 220 Mda, two harboured two plasmids with molecular weight < 220 Mda and no plasmid was detected in the remaining isolates. All the isolates examined showed a distinguishable protein profile using one-dimensional SDS-PAGE. This technique could distinguish one isolate from another. Hybridization studies using R. leguminosarum hup probe did not indicate hup genes in any of the isolates examined.
Soil Biology and Biochemistry 01/1997; · 4.41 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The growth of Frankia cells within alginate beads was inhibited when the amount encapsulated exceeded 0.5 to 2.5 µg protein/ml of beads. Frankia growth was observed not only in the beads incubated in nutrient media (with of without combined N), but also in those incubated in air provided they retained enough nutrients. The results allow some recommendations to be made for the preparation of Frankia inoculants.
World Journal of Microbiology and Biotechnology 01/1994; 10(1):118-121. · 1.35 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The aim of this work was to evaluate the competitive ability between Rhizobium leguminosarum bv trifolii strain U204 used as commercial inoculants in Uruguay for Trifolium repens L. and Trifolium pratense L. and two native strains isolated from inoculated pastures of T. pratense. T126 is an efficient nitrogen fixer and a melanin producer strain; T70 is inefficient and a melanin non-producer strain;
and U204 is very efficient in both hosts but is a melanin non-producer strain. Competitiveness between the strains was determined
in experiments in pots and in growth pouches under controlled conditions. In the last experiment, we evaluated pH of plant
nutrient solution and inoculum ratios. Plant dry weight was determined, and the identification of nodule bacteria was done
using melanin production and DNA fingerprinting (GTG5-PCR). The U204 symbiotic efficiency was not affected by the co-inoculation with the others two native strains. The T70 strain
was a poor competitor when was co-inoculated with one of the effective strains in both experiments. Our results confirmed
a “selective nodulation” because an effective symbiosis occurred preferentially over an ineffective one in Trifolium species. The native effective strain competed with U204 for nodule formation in both clovers species, but the nodule occupancy
depended on the inoculum ratio. The pH of nutritive solution did not affect competition ability of the studied strains. It
may be possible to isolate efficient, competitive, and genetically different native rhizobial strains to be used as inoculant
strains for clover pastures in Uruguay. Both (GTG)5-PCR and melanin production were useful methods to identify nodulating bacteria in competition studies.
Rhizobium leguminosarum bv trifolii
Biology and Fertility of Soils 46(4):419-425. · 3.40 Impact Factor