Showing papers on "Frankia published in 1993"

Hopanoid lipids compose the Frankia vesicle envelope, presumptive barrier of oxygen diffusion to nitrogenase

Abstract: Biological nitrogen fixation in aerobic organisms requires a mechanism for excluding oxygen from the site of nitrogenase activity. Oxygen exclusion in Frankia spp., members of an actinomycetal genus that forms nitrogen-fixing root-nodule symbioses in a wide range of woody Angiosperms, is accomplished within specialized structures termed vesicles, where nitrogen fixation is localized. The lipidic vesicle envelope is apparently a functional analogue of the cyanobacterial heterocyst envelope, forming an external gas-diffusion barrier around the nitrogen-fixing cells. We report here that purified vesicle envelopes consist primarily of two hopanoid lipids, rather than of glycolipids, as is the case in cyanobacteria. One envelope hopanoid, bacteriohopanetetrol phenylacetate monoester, is vesicle-specific. The Frankia vesicle envelope thus represents a layer specific to the locus of nitrogen fixation that is biosynthetically uniquely derived.

Nitrogen translocation between Alnus glutinosa (L.) Gaertn. seedlings inoculated with Frankia sp. and Pinus contorta Doug, ex Loud seedlings connected by a common ectomycorrhizal mycelium

Abstract: Uptake and translocation of nitrogen was studied in laboratory microcosms consisting of Alnus glutinosa (L.) Gaertn., Frankia sp., Paxillus involutus (Fr.) Fr. and Pinus contorta Dougl. ex Loud. P. involutus was shown to form a fully functional ectomycorrhizal association with alder as well as pine, and the seedlings thus became interconnected by a common mycelium. When microcosms were exposed to N-15(2) gas, interplant translocation of N-15 was observed in two out of three experiments. N-15(2) was fixed by Frankia and translocated to all other parts of the system. In the two experiments in which interplant translocation occurred, between 5 and 15 % of the N-15 recovered was found in the pine seedlings. Within seven days, fixed N2 was incorporated into amino acids in the Frankia nodules, translocated to both the A. glutinosa and P. contorta seedlings and incorporated into macromolecules. In alder seedlings, citrulline and ornithine were the free amino acids that had both the highest N-15 enrichment levels and concentrations. In pine, glutamine and citrulline had the highest N-15 concentrations, and glutamine had the highest level of N-15 enrichment. N-15 enrichment levels were greatest in the nodules, at between 5.5 and 29 % in the different amino acids and 12 % in the macromolecular fraction. Enrichment levels decreased with increasing distance from the nodules. The uptake and translocation of N-15 applied as (NH4Cl)-N-15 to the mycelium was also studied. N-15 was incorporated into amino acids in the mycelium and translocated further in this form. Generally, free amino acids had high N-15 enrichment levels in the mycelium, decreasing along the translocation pathway. Citrulline and glutamine were the amino acids with highest N-15 concentrations in all parts of the system. N-15 was also found in the macromolecular fraction. (Less)

Typing method for N2-fixing bacteria based on PCR-F — application to the characterization of Frankia strains

Abstract: DNA sequences of an intergenic spacer (IGS) and parts of genes in the nif cluster were amplified by the polymerase chain reaction (PCR) using two primers derived from nifD- and nifK-conserved sequences. The PCR products were cleaved by ten 4-base cutting restriction enzymes and the restriction patterns were used as fingerprints to type Frankia strains. The feasability of this PCR-RFLP method for typing Frankia strains was investigated on Frankia reference strains belonging mainly to the Elaeagnaceae infectivity group but also on new Frankia isolates and on other N2-fixing microorganisms. By modulating the stringency of the amplifications, we showed the method allowed to target either Frankia strains or the whole N2-fixing microbial community. DNA digestion patterns were used to estimate the sequence divergence between the Frankia nifD-K fragment. The estimated relationships deduced from these genotypic data correlated well with established Frankia taxonomic schemes.

Whole-Cell Hybridization of Frankia Strains with Fluorescence- or Digoxigenin-Labeled, 16S rRNA-Targeted Oligonucleotide Probes.

Abstract: Whole-cell hybridization with non-radioactively labeled oligonucleotide probes was used to detect and identify Frankia strains in pure cultures and in nodules. Digoxigenin-labeled probes, which were detected with antibody-alkaline phosphatase conjugates, were more suitable for in situ detection of Frankia strains than fluorescent probes since the sensitivity of the former was higher and problems arising from the autofluorescence of cells and plant material were avoided. Successful detection of Frankia strains in paraformaldehyde-fixed cell material with digoxigenin-labeled oligonucleotide probes depended on pretreatments to permeabilize the cells. Specific hybridization signals on vesicles were obtained after lysozyme pretreatment (1 mg ml-1 for 30 min at 20°C). Reliable penetration of the antibody-enzyme conjugate into hyphae required additional washing with the detergent Nonidet P-40 (0.1%) and toluene (1% in ethanol) after lysozyme treatment. Identification of Frankia vesicles in nodule homogenates was possible only after the removal of the polysaccharide capsule surrounding the vesicles. Incubation with H2O2 (15% in water for 1 h at room temperature) before lysozyme and detergent treatments was found to facilitate specific hybridization. No filaments or spores could be detected in nodule homogenates. This technique should be a powerful tool in the identification of Frankia isolates, in the characterization of as-yet-uncultured nodule populations, and in the confirmation of the origin of unusual Frankia isolates.

Frankia in the rhizosphere of nonhost plants: A comparison with root-associated N2-fixing Enterobacter, Klebsiella and Pseudomonas

Abstract: Bacterial growth in the rhizosphere and resulting changes in plant growth parameters were studied in small aseptic seedlings of birch (Betula pendula and B. pubescens) and grasses (Poa pratensis and Festuca rubra). The seedlings were inoculated with three Frankia strains (Ai1a and Ag5b isolated from native Alnus root nodules and Ai17 from a root nodule induced by soil originating from a Betula pendula stand), and three associative N2-fixing bacteria (Enterobacter agglomerans, Klebsiella pneumoniae and Pseudomonas sp., isolated from grass roots). Microscopic observations showed that all the Frankia strains were able to colonize and grow on the root surface of the plants tested without addition of an exogenous carbon source. No net growth of the associative N2-fixers was observed in the rhizosphere, although inoculum viable counts were maintained over the experimental period. Changes in both the biomass and morphology of plant seedlings in response to bacterial inoculation were recorded, which were more dependent on the plant species than on the bacterial strain.

Mineral nutrition in the tripartite interaction between Frankia, Glomus and Alnus at different soil phosphorus regimes

Abstract: SUMMARY Phosphate uptake by a tripartite association involving Frankia, Glomus and Alnus was studied in containerized seedlings of Alnus nepalensis D. Don. The response of non-mycorrhizal plants to P fertilization was more pronounced than their mycorrhizal counterparts. The yield of nodulated mycorrhizal plants was greater at low than at high P doses. At the highest P application, however, reduction in nodulation as well as nitrogenase activity was observed. Mycorrhizal infection was reduced by phosphate application, but markedly stimulated nodulation in Alnus seedlings. The nitrogen content of the nodule was higher than that of the shoot of nodulated mycorrhizal plants. Nodule dry weight, nitrogenase activity and nodule nitrogen content increased with increase in P application up to quantities typical of those in soil, after which it declined.

Differentiation of Frankia strains by their electrophoretic patterns of intracellular esterases and aminopeptidases

Abstract: SUMMARY: The closely related Frankia strains BR, S21 and Thr, isolated from the genus Casuarina, Allo2 and Dec from the genus Allocasuarina, and G80 from the genus Gymnostoma, could be distinguished by their esterase zymograms after ultra-low gelling point agarose-polyacrylamide electrophoresis. The kanamycin-resistant derivatives S21-kR and BR-kR could also be differentiated from their kanamycin-sensitive parental strains. Different patterns of intracellular esterases could be obtained by using β-naphthyl propionate or 3-indoxyl acetate as substrates. The substrate 5-bromo-4-chloro-3-indoxyl acetate proved particularly useful, revealing a variety of esterases from Gymnostoma isolates. Zymograms of aminopeptidases from all strains were found to be quite similar. Nevertheless, they allowed differentiation of Frankia strains BR and S21 from their kanamycin-resistant derivatives. Aminopeptidase and esterase zymograms obtained from Gymnostoma isolates were markedly different from all others. Zymograms of esterases and aminopeptidases may prove useful for the identification of some other Frankia strains.

Avian dispersal of Frankia

Abstract: Nests of six common bird species in central Illinois, U.S.A. were collected and examined for the presence of Frankia capable of infecting Alnus glutinosa and Elaeagnus umbellata. Serial dilutions of nest extracts were used in a bioassay to estimate the number of Frankia nodulation units for these two host species in each nest. Nests of two bird species contained soil as a nest component and had high concentrations of Frankia nodulation units. Nests of two bird species that did not use soil in nest building also had relatively high levels of Frankia. Results indicate that some bird species can transport Frankia, possibly by moving soil for nest building and also by other unknown mechanisms. Key words: actinorhizae, bioassay, bird nests, Frankia dispersal, Alnus glutinosa, Elaeagnus umbellata.

Molecular phylogeny of the symbiotic actinomycetes of the genus Frankia matches host-plant infection processes.

Abstract: Nucleotide sequences of approximately 213 bp of the nif H-D intergene and the beginning of nifD were determined for symbiotic Frankia isolates from the major host-infectivity groups. This region of the nif operon is variable enough to classify most infective Frankia strains at the species level. Phylogenetic inferences from these sequences are in agreement with the 16S rRNA-derived phylogeny of the genus and, thus, are in favor of an intrageneric evolution of nif genes by orthology. Phylogenetic lineages derived from combined nifH-D intergene and partial nifD and 16S rRNA sequences are supported for at least 93% of bootstrap replicates and are useful for investigating evolutionary relationships of the genus and symbiotic properties of this microorganism. The genus Frankia is divided into two major phylogenetic clusters that match with the separation of species according to the mechanism of infection of actinorhizal plants. One cluster groups species strictly adapted to the mechanism of root hair infection (RHI), and the other groups species adapted to the mechanism of direct intercellular penetration. In the RHI cluster, the species infective on Casuarina plants appears to have emerged from strains infective on Alnus. The concordance between the symbiotic properties and the molecular phylogeny of Frankia strains indicates a major role for the host plant in the evolution and speciation of the genus Frankia.

Characterization of native Frankia strains isolated from chilean shrubs (Rhamnaceae)

Abstract: Nine native Frankia strains were isolated from root nodules of four chilean actinorhizal plants (Rhamnaceae). The strains were designated as ChI1, ChI2, ChI3 and ChI4 from Colletia hystrix; ReI4 and ReI6 from Retanilla ephedra; TqI12 and TqI15 from Talguenea quinquinervis and TtI42 from Trevoa trinervis. By scanning electron microscopy, all the strains exhibited similar actinomycetal structures: hyphae, sporangia and vesicles. The growth patterns of the isolates in BAP medium were similar. All showed a lag phase of approximately 6–7 days, then exhibited a logarithmic phase, except the ReI4 strain which seems to follow a linear growth pattern. A common feature of all the strains was a rapid loss of biomass at the end of the growth phase. All native strains grew on BAP medium supplemented with glucose. In six out of nine strains, the glucose was the best of the carbon sources tested. However, the strains differed in their ability to use other carbon sources such as arabinose, mannitol, maltose, succinate, sucrose, pyruvate, propionate and galactose. The isolates were sensitive to six antibiotics assayed (ampicillin, penicillin G, rifampicin, chloramphenicol, erythromycin and kanamycin). Using the acetylene reduction assay, the nitrogenase activity of the strains was determined. All strains grown in BAP medium lacking a combined nitrogen source were able to reduce acetylene ‘in vitro’.

Identification and Localization of Frankia Strains in Alnus Nodules by In Situ Hybridization of nif H mRNA with Strain-Specific Oligonucleotide Probes

Abstract: In situ hybridization of Frankia mRNA with specific probes was used to localize the strains Ar13 and AcoN24d in Alnus nodules obtained after inoculation with one or both strains. The probes consisted of 18-mer oligonucleotides, complementary to strain-specific sequences located within the nif H gene. Sections of nodules inoculated with only one strain revealed a specific hybridization between the probe and the corresponding Frankia strain mRNA. In sections of dually-inoculated nodules the presence of the strain AcoN24d in the nodule was clearly shown whereas those of the strain Ar13 could not be detected. This suggests that the strain Ar13 is less infective than the strain AcoN24d and is not present within the nodule

Plant function in nodulation and nitrogen fixation in legumes

Abstract: While it is accepted that the understanding of the process of nitrogen fixation is best carried out in free-living nitrogen fixing organisms like Klebsiella pneumoniae, Azotobacter and Rhodopseudomonas, it is the symbiotic relationship between a nitrogen fixing prokaryote like Rhizobium, Bradyrhizobium or Frankia with a eukaryotic host plant that has stimulated the interest of plant biologists, microbial geneticists and pathologists.

Modification of Polypeptide Patterns During Nodule Development in the Frankia-Alnus Symbiosis

Abstract: The soluble proteins from nodules (actinorhizae), roots of Alnus glutinosa (L.) Gaertn., and free-living Frankia alni subsp. pommerii isolate ACNl AG cultures were analysed in order to investigate if any actinorhiza-specific proteins were induced by the inoculation of clonal plantlets (AG2) by Frankia. Comparisons of protein patterns from actinorhizae and non-infected roots, obtained by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE), showed that three polypeptides of molecular weights 36, 50 and 61 kD could be detected in actinorhizae but not in roots. Immunoblotting techniques using heterologous antisera \"directed\" against members of the nitrogenase enzyme complex identified the 36 and 61 kD polypeptides as the Fe protein and MoFe protein of the Frankia nitrogenase. Analysis of the protein extracts by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) revealed five additional nodule-specific polypeptides in developing actinorhizae.

Differential Gene Expression in the Development of Actinorhizal Root Nodules

Abstract: Actinorhizal root nodules form as a result of the interaction of actinomycetes in the genus Frankia with the appropriate host plant roots. In the actinorhizal symbiosis with Alnus, the first easily detectable sign of interaction between the plant and bacterial partners is the extensive deformation of plant root hairs. This root hair deformation which is detectable in a matter of hours has been shown not to require direct contact between bacteria and host plant (Prin, Rougier, 1987). There appears to be an as yet unidentified diffusible factor synthesized or released by frankiae in response to exposure to host plant root exudate in a manner analogous to the rhizobia/legume signaling system. Root hair deformation is followed by penetration of the root hair by Frankia filaments and the initiation of cortical cell divisions leading to prenodule formation (Berry, Sunell, 1990). The colonization of prenodule tissue is followed by the induction of a lateral root primordium in the pericycle. As the lateral root primordium grows through the infected prenodule tissue the postmeristematic cells of the now-nodule primordium are themselves infected with the microsymbiont which rapidly proliferates within host cells and begins to fix nitrogen. The nodule meristem bifurcates giving rise to the lobed nodules characteristic of Alnus.

Characterization of uncultured Frankia strains by 16S rRNA sequence analysis

Abstract: Studies on the root nodules of Coriaria nepalensis using light and electron microscope revealed that the nodule structure and morphology of the endophyte is unique among the actinorhizal plants and similar only to those of Datisca cannabina. Plant cells containing the endophyte were relatively enlarged as compared to the non-infected cells. Transverse sections of the nodules revealed that the infected cells form a compact kidney-shaped zone around the stele which is located on one side of the nodule lobe. Inside the host cell, the hyphae of the endophyte were located in the peripheral region of the cytoplasm whilst the elongate vesicles were present near the central vacuole. Host cell mitochondria were abundant and mostly found in close vicinity of the hyphal/vesicular junction of the endophyte. In situ hybridization studies showed localization of the nifH mRNA within the elongate vesicles of the endophyte. The results indicate that the elongate vesicles of the Coriaria nodule endophyte are functionally identical to the spherical vesicles of the Alnus endophyte. Acetylene reduction (C 2 H 2 reduction) and uptake hydrogenase activity of the root nodules of Coriaria nepalensis and Datisca cannabina were measured to study seasonal fluctuations in the enzyme activities. Nitrogenase activity of the nodules of both plants showed biphasic curves with peaks in spring and late summer. Less than 15% of the enzyme activity was retained by the nodules in winter. Results showed that maximum nitrogenase activity coincides with the period of vigorous plant growth in both hosts. Uptake hydrogenase activity was detected in nodules of both plants throughout the year. The peak enzyme activity in both Coriaria and Datisca nodules was recorded in May. Vesicle cluster fraction of the crushed nodule suspensions showed the highest uptake hydrogenase activity, indicating that the enzyme is associated with the endophyte. Nine Frankia-like a ctinomycetes were isolated from root nodules of Coriaria nepalensis. All isolates formed hyphae and sporangia typical of Frankia, but failed to induce nodules on Coriaria seedlings, or reduce acetylene in pure culture. The relationship of these strains to atypical and typical Frankia strains isolated from other actinorhizal plants and various other actinomycetes was investigated by comparing fatty acid patterns. All Frankia strains, including atypical isolates, showed fatty acid profiles distinct from those of Actinomyces , Geodermatophilus , Nocardia , Mycobacterium and Streptomyces. For Frankia strains a characteristic pattern of five fatty acids was found that comprised 75% or more of the total content. Three subgroups were identified among 30 Frankia strains compared. Atypical strains isolated from Coriaria were found in the largest subgroup which contained most Frankia strains from other hosts, while ineffective strains from other hosts were distributed in all three subgroups. Non-infective, atypical strains isolated from Coriaria nodules were characterized further by partial 16S rRNA sequence analysis. Ribosomal RNA isolated from all atypical strains hybridized strongly with a Frankia genus probe and indicated that the isolates did belong to the genus Frankia. This was confirmed for two of the isolates (Cn3 and Cn7) from Coriaria nodules by comparison of partial 16S rRNA sequences of the cloned amplification products. Both isolates showed about 95% sequence homology to those of the confirmed Frankia strains from other hosts. Similar high homology values were obtained when 16S rRNA sequences of Cn3 and Cn7 were compared with those of the amplification products obtained directly from nodules of Coriaria nepalensis. In two variable regions compared, none of the isolates showed identical sequences to those obtained from nodules. These results suggest that the isolates are members of the genus Frankia , but different from the strain identified within the root nodules of Coriaria by 16S rRNA sequence analysis. The endophyte of the root nodules of Datisca cannabina was identified as Frankia by sequence analysis of the partial 16S rRNA gene, amplified directly from the nodules by polymerase chain reaction. Moreover, 16S rRNA sequence analysis indicated that the endophyte of Datisca nodules is closely related to that of the Coriaria nodule endophyte, to which it also resembles morphologically in the symbiotic state. Relatedness of the endophytes of Coriaria and Datisca nodules was further proved by the closely related nifH sequences obtained from the nodules by PCR. 16S rRNA sequence analysis of the non-infective atypical strain Dc2 obtained from the Datisca nodules revealed its close relationship to the genus Frankia. Nodulation in Datisca was achieved with crushed nodule suspensions from both Coriaria and Datisca , whereas various pure Frankia strains failed to induce nodulation. The origin of the endophyte in Datisca nodules induced by crushed nodules of Coriaria collected from Murree (Pakistan) was investigated by comparing partial 16S rRNA sequences with those of the endophytes of both plants. The sequences in the variable region were found to be identical to those of Coriaria nodule endophyte, confirming that the endophyte of Coriaria can cross-nodulate Datisca plants. Acetylene reduction by the root nodules indicated effectiveness of the nodules. Coriaria seedlings could only be nodulated by crushed nodule suspensions of Coriaria nepalensis. All pure cultures of Frankia including atypical strains used as single inoculum or in combination with the nodule filtrate, failed to induce nodulation on Coriaria seedlings. Sequence information obtained from the root nodules of Coriaria and Datisca by PCR amplification of partial 16S rRNA gene of the endophyte, was used to develop an oligonucleotide probe. The probe was designed against the V6 variable region of the 16S rRNA that was identical in the 16S rRNA of the endophytes of Coriaria and Datisca. The probe did not cross-react with RNA of typical and atypical Frankia strains isolated from Alnus , Casuarina , Colletia , Comptonia , Elaeagnus and Hippophae. To investigate the presence of Frankia strains infective on Coriaria and Datisca , soil samples were collected from different areas of Pakistan and used as inoculum. Three types of soil samples i.e. rhizosphere soil, non-rhizosphere soil and soil from sites effected by erosion were used to inoculate seedlings of Coriaria and Datisca. Abundance of compatible Frankia strains in most areas was indicated by profuse nodulation of the host plants, while soil samples from Athmokam and Puddar failed to induce nodulation on Coriaria seedlings. Exceptionally good nodulation of Coriaria and Datisca with soil samples collected from Abbottabad and Kaghan respectively, reflects abundance of compatible Frankia strains in the soils. This also indicates that these soils can be used effectively as an inoculum for large scale inoculation programmes instead of nodules that are difficult to obtain throughout the year. Successful nodulation of plants inoculated with soil suspensions can confirm the existence of compatible Frankia cells, but the possibility of the presence of more than one infective strain cannot be ruled out. Genetic diversity among the Frankia strains in Datisca nodules originaly induced by soil inoculum collected from different areas of Pakistan, was determined by sequence analysis of 16S rRNA. Part of the 16S rRNA gene was amplified from nodules and the cloned PCR products were screened initially with a Frankia genus probe and then with the specific probe. Three categories of the clones were identified i.e. those reacting with both probes and those hybridizing with only the Frankia genus probe, or only with the probe specific for the Datisca endophyte. Four types of Frankia sequences and one non -Frankia sequence were identified by sequence analysis of the cloned PCR products. The results suggest the presence of more than one Datisca- compatible Frankia strains in the soils collected from different areas.

Esterase diversity among 46 Frankia strains isolated from Casuarina equisetifolia in West Africa

Abstract: Forty-six Frankia strains isolated from nodules of five Casuarina equisetifolia stands throughout Senegal and Gambia were analyzed for their enzyme electrophoretic profiles and compared with six collection strains. These strains were classified into 14 electrotypes, according to their esterase patterns. One or two electrotypes were predominant in each investigation site whereas other electrotypes corresponded to only one strain each. Esterase electrophoretic polymorphism evidenced heterogeneity of a restricted population of Frankia strains belonging to a single genomic species and indicated the high discriminating power of these enzymes for the study of the ecological repartition of Frankia strains in a tropical region.Key words: Casuarina equisetifolia, Frankia, Senegal, enzyme electrophoresis.

Strains in Alnus Nodules by In Situ Hybridization of nif H mRNA with Strain Specific Oligonucleotide Probes

Abstract: In situ hybridization of Frankia mRNA with specific probes was used to localize the strains Arl3 and AcoN24d in Alnus nodules obtained after inoculation with one or both strains. The probes consisted of 18-mer oligonucleotides, complementary to strain specific sequences located within the nif H gene. Sections of nodules inoculated with only one strain revealed a specific hybridization between the probe and the corresponding Frankia strain mRNA. In sections of dually-inoculated nodules the presence of the strain AcoN24d in the nodule was clearly shown whereas those of the strain Arl3 could not be detected. This suggests that the strain Arl3 is less infective than the strain AcoN24d and is not present within the nodule.

Micropropagation of nitrogen-fixing trees

Abstract: The increase in population and unit energy consumption has resulted in overexploitation of our natural resources, especially forests. The vicious cycles of drought and flood already visible in many parts of the world are probably a reflection of imbalance in nature due to indiscriminate destruction of forests. It is now realized that for the welfare of the human race, it is vital to protect the remaining forest cover from further damage and to reforest the presently denuded areas. Fast growing, hardy, robust, leguminous trees, that enrich the soil with nitrogenous bio-fertilizers, are the prime candidates for reclaiming and revegetating vast wastelands. The nitrogen fixing species not only survive under harsh conditions, but also, over a period of time, they improve the nutritional status of the soil, thus making it suitable for the growth of other species. Nitrogen fixation in higher plants is achieved through a symbiotic association of their roots either with bacteria belonging to the genus Rhizobium or actinomycetes belonging to the group Frankia.

Presence of sporangia of Frankia in the rhizosphere of Discaria (Rhamnaceae)

Abstract: Discaria trinervis and Discaria americana are native actinorhizal plants in Argentina. Discaria seedlings growing in N-free liquid culture, inoculated with dry soils, developed Frankia colonies in the rhizosphere. The occurrence of hyphae, vesicles and sporangia characteristic of Frankia are described in these colonies. The presence of sporangia of Frankia has previously neither been reported in the genus Discaria, nor in the other genera of the tribe Colletieae inside root nodules or outside roots. The infective capacity of the colonies has been demonstrated.

Coordinate increase in activity of proteinase subunits of the 1300-kDa megaproteinase of Frankia strain BR: role of carbon source depletion and extracellular metabolites.

Abstract: We have recently described the presence of a high molecular mass multicatalytic proteinase complex (megaproteinase; 28 S, 1300 kDa) in Frankia strain BR. The complex dissociates into 11 low molecul...

Effects of Environmental Factors on the Nitrogen Fixation Activity in Elaeagnus umbellata

Abstract: The seasonal changes of symbiotic nitrogen-fixation activity and environmental factors of autumn olive plant (Elaeagnus umbellata Thunb.), which is an important constituent species of temperate vegetation and a non-leguminous root nodule plant interacting with Frankia sp., were quantitatively analyzed inthe natural vegetations during hegrowing period. The acetylene redution April and showed two peaks of 133 and in early June and mid September. The nitrogenase activity decreased to 10~30% during hot dry summer frommid June to the end of August, and disappeared during the dormant period of winter. The optimum rhizoshere. diurnal change showed the maximum activity in the mid-day and the minimum in the mid-night. The average contents of total nitrogen in each organ changed in the ranges of 42.5~40.1, 40.2~36.3, 30.3~28.6 and 18.4~16.2mgN for nodule, leaf, root, and stem, respectively. The soil conditions of rhizosphere were weak acidic, ad seasonal variations of and water contents were in the ranges of 48.3~79.5ppm,5.1~13.9ppm, 4.4~ and 14.5~39.4%, respectively.

Nitrogen metabolism of Frankia strain, Cc01, Mg+, At4 and Hr18

Abstract: The composition and levels of amino acids in four Frankia strains isolated from different actinorhizal plants, were determined. Minor differences in the amino acid profiles were noted with GLN (GLU) being the major amino acid in all four strains. Enzyme actives of ammonia metabolism, GS (glutamine synthetase), GOGAT (glutamate synthetase), and GDH (glutamate dehydrogenase), were also measured. In strains At4 and Hr18, GS and GOGAT activity levels were elevated in N2-grown cells but significant amounts of GDH activity were present in ammonia-grown cells. No GDH was detected in strain Cc01 and Mg+. The characters of heat-stable and heat-labile GSs were described. In N2-fixing cells, the ATP and amino acid content was much lower, but ammonia content was higher than in NH inf4 sup+ -grown cells.