Presence and activity of nitrogen-fixing bacteria in Scots pine needles in a boreal forest: a nitrogen-addition experiment

Endophytic nitrogen-fixing bacteria have been detected and isolated from the needles of conifer trees growing in North American boreal forests. Because boreal forests are nutrient-limited, these bacteria could provide an important source of nitrogen for tree species. This study aimed to determine their presence and activity in a Scandinavian boreal forest, using immunodetection of nitrogenase enzyme subunits and acetylene-reduction assays of native Scots pine (Pinus sylvestris L.) needles. The presence and rate of nitrogen fixation by endophytic bacteria were compared between control plots and fertilized plots in a nitrogen-addition experiment. In contrast to the expectation that nitrogen-fixation rates would decline in fertilized plots, as seen, for instance, with nitrogen-fixing bacteria associated with bryophytes, there was no difference in the presence or activity of nitrogen-fixing bacteria between the two treatments. The extrapolated calculated rate of nitrogen fixation relevant for the forest stand was 20 g N ha-1 year-1, which is rather low compared with Scots pine annual nitrogen use but could be important for the nitrogen-poor forest in the long term. In addition, of 13 colonies of potential nitrogen-fixing bacteria isolated from the needles on nitrogen-free media, 10 showed in vitro nitrogen fixation. In summary, 16S rRNA sequencing identified the species as belonging to the genera Bacillus, Variovorax, Novosphingobium, Sphingomonas, Microbacterium and Priestia, which was confirmed by Illumina whole-genome sequencing. Our results confirm the presence of endophytic nitrogen-fixing bacteria in Scots pine needles and suggest that they could be important for the long-term nitrogen budget of the Scandinavian boreal forest.

More than protection: the function of TiO2 interlayers in hematite functionalized Si photoanodes

Worldwide significant efforts are ongoing to develop devices that store solar energy as fuels. In one such approach, solar energy is absorbed by semiconductors and utilized directly by catalysts at their surfaces to split water into H2 and O2. To protect the semiconductors in these photo-electrochemical cells (PEC) from corrosion, frequently thin TiO2 interlayers are applied. Employing a well-performing photoanode comprised of 1-D n-Si microwires (MWs) covered with a mesoporous (mp) TiO2 interlayer fabricated by solution processing and functionalized with α-Fe2O3 nanorods, we studied here the function of this TiO2 interlayer by high-energy resolution fluorescence detected X-ray absorption near edge structure (HERFD-XANES) spectroscopy, along with X-ray emission spectroscopy (XES) and standard characterization techniques. Our data reveal that the TiO2 interlayer not only protects the n-Si MW surface from corrosion, but that it also acts as a template for the hydrothermal growth of α-Fe2O3 nanorods and improves the photocatalytic efficiency. We show that the latter effect correlates with the presence of stable oxygen vacancies at the interface between mp-TiO2 and α-Fe2O3, which act as electron traps and thereby substantially reduce the charge recombination rate at the hematite surface.

Candidatus Frankia nodulisporulans sp. nov., an Alnus glutinosa-infective Frankia species unable to grow in pure culture and able to sporulate in-planta

We describe a new Frankia species, for three non-isolated strains obtained from Alnus glutinosa in France and Sweden, respectively. These strains can nodulate several Alnus species (A. glutinosa, A. incana, A. alnobetula), they form hyphae, vesicles and sporangia in the root nodule cortex but have resisted all attempts at isolation in pure culture. Their genomes have been sequenced, they are significantly smaller than those of other Alnus-infective species (5Mb instead of 7.5Mb) and are very closely related to one another (ANI of 100%). The name Candidatus Frankia nodulisporulans is proposed. The GenBank/EMBL/DDBJ accession numbers for the 16S rRNA gene and draft genome sequences reported in this study for AgTrS, AgUmASt1 and AgUmASH1 are MT023539/LR778176/LR778180 and NZ_CADCWS000000000.1/CADDZU010000001/CADDZW010000001, respectively.

Effects of light intensity on growth and lipid production in microalgae grown in wastewater

BACKGROUND

Cultivation of microalgae in wastewater could significantly contribute to wastewater treatment, biodiesel production, and thus the transition to renewable energy. However, more information on effects of environmental factors, including light intensity, on their growth and composition (particularly fatty acid contents) is required. Therefore, we investigated the biomass and fatty acid production of four microalgal species, isolated in the Northern hemisphere and grown at three light intensities (50, 150 and 300 μE m^-2 s^-1).

RESULTS

Increases in light intensities resulted in higher biomass of all four species and, importantly, raised fatty acid contents of both Desmodesmus sp. and Scenedesmus obliquus. Fourier-transform IR spectrometry analysis showed that the increases in fatty acid content were associated with reductions in protein, but not carbohydrate, contents. Assessment of fatty acid composition revealed that increasing light intensity led to higher and lower contents of oleic (18:1) and linolenic (18:3) acids, respectively. The microalgae consumed more than 75% of the nitrogen and phosphorus present in the wastewater used as growth medium.

CONCLUSION

The results show the importance of optimizing light intensities to improve fatty acid production by microalgae and their quality as sources of biodiesel. In addition, increase in fatty acid content is associated with decrease in protein content.

A microstructured p-Si photocathode outcompetes Pt as a counter electrode to hematite in photoelectrochemical water splitting

Herein, we communicate about an Earth-abundant semiconductor photocathode (p-Si/TiO2/NiOx) as an alternative for the rare and expensive Pt as a counter electrode for overall photoelectrochemical water splitting. The proposed photoelectrochemical (PEC) water-splitting device mimics the "Z"-scheme observed in natural photosynthesis by combining two photoelectrodes in a parallel-illumination mode. A nearly 60% increase in the photocurrent density (Jph) for pristine α-Fe2O3 and a 77% increase in the applied bias photocurrent efficiency (ABPE) were achieved by replacing the conventionally used Pt cathode with an efficient, cost effective p-Si/TiO2/NiOx photocathode under parallel illumination. The resulting photocurrent density of 1.26 mA cm-2 at 1.23VRHE represents a new record performance for hydrothermally grown pristine α-Fe2O3 nanorod photoanodes in combination with a photocathode, which opens the prospect for further improvement by doping α-Fe2O3 or by its decoration with co-catalysts. Electrochemical impedance spectroscopy measurements suggest that this significant performance increase is due to the enhancement of the space-charge field in α-Fe2O3.

Mixotrophic and heterotrophic production of lipids and carbohydrates by a locally isolated microalga using wastewater as a growth medium

The biomass production and changes in biochemical composition of a locally isolated microalga (Chlorella sp.) were investigated in autotrophic, mixotrophic and heterotrophic conditions, using glucose or glycerol as carbon sources and municipal wastewater as the growth medium. Both standard methods and Multivariate Curve Resolution-Alternating Least Squares (MCR-ALS) analysis of data acquired by Fourier-transform IR (FTIR) spectrometry showed that autotrophic and mixotrophic conditions promoted carbohydrate accumulation, while heterotrophic conditions with glycerol resulted in the highest lipid content and lowest carbohydrate content. Heterotrophic conditions with glycerol as a carbon source also resulted in high oleic acid (18:1) contents and low linolenic acid (18:3) contents, and thus increasing biodiesel quality. The results also show the utility of MCR-ALS for analyzing changes in microalgal biochemical composition.

Draft Genome Sequence of the Symbiotic Frankia Sp. Strain KB5 Isolated from Root Nodules of Casuarina equisetifolia

Frankia sp. strain KB5 was isolated from Casuarina equisetifolia and previous studies have shown both nitrogenase and uptake hydrogenase activities under free-living conditions. Here, we report 5.5-Mbp draft genome sequence with a G+C content of 70.03 %, 4,958 candidate protein-encoding genes, and 2 rRNA operons.

Expression of fungal acetyl xylan esterase in Arabidopsis thaliana improves saccharification of stem lignocellulose

Cell wall hemicelluloses and pectins are O-acetylated at specific positions, but the significance of these substitutions is poorly understood. Using a transgenic approach, we investigated how reducing the extent of O-acetylation in xylan affects cell wall chemistry, plant performance and the recalcitrance of lignocellulose to saccharification. The Aspergillus niger acetyl xylan esterase AnAXE1 was expressed in Arabidopsis under the control of either the constitutively expressed 35S CAMV promoter or a woody-tissue-specific GT43B aspen promoter, and the protein was targeted to the apoplast by its native signal peptide, resulting in elevated acetyl esterase activity in soluble and wall-bound protein extracts and reduced xylan acetylation. No significant alterations in cell wall composition were observed in the transgenic lines, but their xylans were more easily digested by a β-1,4-endoxylanase, and more readily extracted by hot water, acids or alkali. Enzymatic saccharification of lignocellulose after hot water and alkali pretreatments produced up to 20% more reducing sugars in several lines. Fermentation by Trametes versicolor of tissue hydrolysates from the line with a 30% reduction in acetyl content yielded ~70% more ethanol compared with wild type. Plants expressing 35S:AnAXE1 and pGT43B:AnAXE1 developed normally and showed increased resistance to the biotrophic pathogen Hyaloperonospora arabidopsidis, probably due to constitutive activation of defence pathways. However, unintended changes in xyloglucan and pectin acetylation were only observed in 35S:AnAXE1-expressing plants. This study demonstrates that postsynthetic xylan deacetylation in woody tissues is a promising strategy for optimizing lignocellulosic biomass for biofuel production.

Aspects of nitrogen-fixing Actinobacteria, in particular free-living and symbiotic Frankia

Studies of nitrogen-fixing properties among the Gram-positive Actinobacteria revealed that some species of Arthrobacter, Agromyces, Corynebacterium, Mycobacterium, Micromonospora, Propionibacteria and Streptomyces have nitrogen-fixing capacity. This is also valid for Frankia that fix nitrogen both in free-living and in symbiotic conditions. Frankia symbiosis results from interaction between the Frankia bacteria and dicotyledonous plants, that is, actinorhiza. These plants, which are important in forestry and agroforestry, form, together with the legumes (Fabales), a single nitrogen-fixing clade. It has been shown that a receptor-like kinase gene, SymRK, is necessary for nodulation in actinorhizal plants as well as in legumes and arbuscular mycorrhizal fungi. Recently, the involvement of isoflavonoids as signal molecules during nodulation of an actinorhizal plant was shown. The genome sizes of three Frankia species, Frankia EANpec, ACN14a and CcI3, are different, revealing a relationship between genome size and geographical distribution. Recent genomic sequencing data of Frankia represent genomes from cluster I to IV, indicating that the genome of DgI is one of the smallest genomes in Frankia. In addition, nonsymbiotic Frankiales such as Acidothermus cellulolyticus, Blastococcus saxoobsidens, Geodermatophilus obscurus and Modestobacter marinus have a variety of genome sizes ranging from 2.4 to 5.57 Mb.

The phylogeny of uptake hydrogenases in Frankia

Uptake hydrogenase is an enzyme that is beneficial for nitrogen fixation in bacteria. Recent studies have shown that Frankia sp. has two sets of uptake hydrogenase genes, organized in synton 1 and synton 2. In the present study, phylogenetic analysis of the structural subunits of hydrogenase syntons 1 and 2 showed a distinct clustering pattern between the proteins of Frankia strains that were isolated from different host plants and non-Frankia organisms. The structural subunits of hydrogenase synton 1 of Frankia sp. CpI1, Frankia alni ACN14a, and F. alni AvCI1 were grouped together while those of Frankia spp. CcI3, KB5, UGL140104, and UGL011102 formed another group. The structural subunits of hydrogenase synton 2 of F. alni ACN14a and Frankia spp. CcI3 and BCU110501 grouped together, but those of Frankia spp. KB5 and CpI1, F. alni ArI3, and F. alniAvCI1 comprised a separate group. The structural subunits of hydrogenase syntons 1 and 2 of Frankia sp. EAN1pec were more closely related to those of non-Frankia bacteria, i.e., Streptomyces avermitilis and Anaeromyxobacter sp., respectively, than to those of other Frankia strains, suggesting the occurrence of lateral gene transfer between these organisms. In addition, the accessory Hyp proteins of hydrogenase syntons 1 and 2 of F. alni ACN14a and Frankia sp. CcI3 were shown to be phylogenetically more related to each other than to those of Frankia EAN1pec.

Ecosystem controls on nitrogen fixation in boreal feather moss communities

N fixation in feather moss carpets is maximized in late secondary successional boreal forests; however, there is limited understanding of the ecosystem factors that drive cyanobacterial N fixation in feather mosses with successional stage. We conducted a reciprocal transplant experiment to assess factors in both early and late succession that control N fixation in feather moss carpets dominated by Pleurozium schreberi. In 2003, intact microplots of moss carpets (30 cm x 30 cm x 10-20 cm deep) were excavated from three early secondary successional (41-101 years since last fire) forest sites and either replanted within the same stand or transplanted into one of three late successional (241-356 years since last fire) forest sites and the transverse was done for late successional layers of moss. Moss plots were monitored for changes in N-fixation rates by acetylene reduction (June 2003-September 2005) and changes in the presence of cyanobacteria on moss shoots by microscopy (2004). Forest nutrient status was measured using ionic resin capsules buried in the humus layer. Late successional forests exhibit high rates of N fixation and consistently high numbers of cyanobacteria on moss shoots, but low levels of available N. Conversely, early successional forests have higher N availability and have low rates of N fixation and limited presence of cyanobacteria on moss shoots. Transplantation of moss carpets resulted in a significant shift in presence and activity of cyanobacteria 1 year after initiation of the experiment responding to N fertility differences in early versus late successional forests.

Genome characteristics of facultatively symbiotic Frankia sp. strains reflect host range and host plant biogeography

Soil bacteria that also form mutualistic symbioses in plants encounter two major levels of selection. One occurs during adaptation to and survival in soil, and the other occurs in concert with host plant speciation and adaptation. Actinobacteria from the genus Frankia are facultative symbionts that form N(2)-fixing root nodules on diverse and globally distributed angiosperms in the "actinorhizal" symbioses. Three closely related clades of Frankia sp. strains are recognized; members of each clade infect a subset of plants from among eight angiosperm families. We sequenced the genomes from three strains; their sizes varied from 5.43 Mbp for a narrow host range strain (Frankia sp. strain HFPCcI3) to 7.50 Mbp for a medium host range strain (Frankia alni strain ACN14a) to 9.04 Mbp for a broad host range strain (Frankia sp. strain EAN1pec.) This size divergence is the largest yet reported for such closely related soil bacteria (97.8%-98.9% identity of 16S rRNA genes). The extent of gene deletion, duplication, and acquisition is in concert with the biogeographic history of the symbioses and host plant speciation. Host plant isolation favored genome contraction, whereas host plant diversification favored genome expansion. The results support the idea that major genome expansions as well as reductions can occur in facultative symbiotic soil bacteria as they respond to new environments in the context of their symbioses.

Physiological and molecular diversity of feather moss associative N2-fixing cyanobacteria

Cyanobacteria colonizing the feather moss Pleurozium schreberi were isolated from moss samples collected in northern Sweden and subjected to physiological and molecular characterization. Morphological studies of isolated and moss-associated cyanobacteria were carried out by light microscopy. Molecular tools were used for cyanobacteria identification, and a reconstitution experiment of the association between non-associative mosses and cyanobacteria was conducted. The influence of temperature on N2 fixation in the different cyanobacterial isolates and the influence of light and temperature on N2-fixation rates in the moss were studied using the acetylene reduction assay. Two different cyanobacteria were effectively isolated from P. schreberi: Nostoc sp. and Calothrix sp. A third genus, Stigonema sp. was identified by microscopy, but could not be isolated. The Nostoc sp. was found to fix N2 at lower temperatures than Calothrix sp. Nostoc sp. and Stigonema sp. were the predominant cyanobacteria colonizing the moss. The attempt to reconstitute the association between the moss and cyanobacteria was successful. The two isolated genera of cyanobacteria in feather moss samples collected in northern Sweden differ in their temperature optima, which may have important ecological implications.

Molecular characterization of uptake hydrogenase in Frankia

A molecular characterization of uptake hydrogenase in Frankia was performed by using two-dimensional gel electrophoresis, matrix-assisted laser-desorption ionization-time-of-flight mass spectrometry, PCR amplification and Southern blotting. A polypeptide of approx. 60 kDa was recognized in Frankia UGL011102, AVCI1 and KB5 on the two-dimensional gel by blotting with Ralstonia eutropha (Hox G) antibody. Further analysis by MS resulted in a peptide 'fingerprint', which was similar to the membrane-bound hydrogenase 2 large subunit (HYD2) in Escherichia coli. In addition, a 127 bp PCR fragment could also be amplified from Frankia AVCI1, which gave a 76% similarity with the large subunit of hydrogenase in, e.g., Azotobacter chrococcum, Bradyrhizobium japonicum and Rhizobium leguminosarum. Although immunological similarity between the small subunit of Frankia hydrogenase and that of other organisms has not yet been found, a PCR product of 500 bp could be amplified from the local source of Frankia, the analysis of which gave 69 and 67% identity with the small subunit of hydrogenases in B. japonicum and R. leguminosarum respectively. A Southern-blot analysis further indicated evidence for the presence of the small hydrogenase subunit in other Frankia strains, i.e. KB5, AvcI1 and CcI3.

A hydrogen-evolving enzyme is present in Frankia sp. R43

The ability to evolve hydrogen using methyl viologen as an electron donor was assayed in the nitrogen-fixing actinomycetes Frankia sp. R43 and Frankia sp. KB5. To further examine the nature of hydrogen-evolving enzymes that may be present in these organisms immunological studies were performed. Under anaerobic conditions (both nitrogen-limiting and nitrogen-containing) Frankia sp. R43 but not Frankia sp. KB5 evolved hydrogen,which was not linked to NAD-reducing activity. Immunological analysis of total protein from Frankia sp. R43 and Frankia sp. KB5 using an antiserum raised against Ralstonia eutropha HoxF, recognized an antigen in Frankia sp. R43 but not in Frankia sp. KB5. Immunogold labeling using antibodies raised against the R. eutropha HoxH recognized sites in both hyphae and vesicles of Frankia sp. R43, but not in Frankia sp. KB5. Based on these physiological and immunological findings, we conclude that Frankia sp. R43 has a hydrogen-evolving hydrogenase.

Biodiversity of hydrogenases in Frankia

Eighteen Frankia strains originally isolated from nine different host plants were used to study the biodiversity of hydrogenase in Frankia. In the physiological analysis, the activities of uptake hydrogenase and bidirectional hydrogenase were performed by monitoring the oxidation of hydrogen after supplying the cells with 1% hydrogen and the evolution of hydrogen using methyl viologen as an electron donor, respectively. These analyses were supported with a study of the immunological relationship between Frankia hydrogenase and other different known hydrogenases from other microorganisms. Uptake hydrogenase activity was recorded from all the Frankia strains investigated. A methyl-viologen-mediated hydrogen evolution was recorded from only four Frankia strains irrespective of the source of Frankia. From the immunological and physiological studies, we here report that there are at least three types of hydrogenases in Frankia: Ni-Fe uptake hydrogenase, hydrogen-evolving hydrogenase, and [Fe]-hydrogenase. An immunogold localization study, by cryosection technique, of the effect of nickel on the intercellular distribution of hydrogenase proteins in Frankia indicated that nickel affects the transfer of hydrogenase proteins into the membrane.

Laser-based micromanipulation for separation and identification of individual Frankia vesicles

In studies of symbiotic efficiency it is of great importance to identify and separate individual Frankia strains from a nodule. Therefore, a new laser-based micromanipulation technique has been developed in which individual vesicles from root nodules of two Frankia-Alnus symbioses have been successfully cut loose and separated from clusters of vesicles in sterile conditions under light microscopy using a laser scalpel and optical tweezers. Vesicles from the Alnus incana-Frankia AvCI1 symbiosis were successfully isolated and grown in culture using this technique. The DNA from both Frankia sources was amplified by polymerase chain reaction (PCR). The work shows that a combination of laser-based manipulation techniques and PCR can be used for the separation and study of individual vesicles. This novel laser-based micromanipulation technique opens up various new possibilities, for instance, to study whether several Frankia strains can grow simultaneously in the same root nodule.

Quantifying nitrogen-fixation in feather moss carpets of boreal forests

Biological nitrogen (N) fixation is the primary source of N within natural ecosystems, yet the origin of boreal forest N has remained elusive. The boreal forests of Eurasia and North America lack any significant, widespread symbiotic N-fixing plants. With the exception of scattered stands of alder in early primary successional forests, N-fixation in boreal forests is considered to be extremely limited. Nitrogen-fixation in northern European boreal forests has been estimated at only 0.5 kg N ha(-1) yr(-1); however, organic N is accumulated in these ecosystems at a rate of 3 kg N ha(-1) yr(-1) (ref. 8). Our limited understanding of the origin of boreal N is unacceptable given the extent of the boreal forest region, but predictable given our imperfect knowledge of N-fixation. Herein we report on a N-fixing symbiosis between a cyanobacterium (Nostoc sp.) and the ubiquitous feather moss, Pleurozium schreberi (Bird) Mitt. that alone fixes between 1.5 and 2.0 kg N ha(-1) yr(-1) in mid- to late-successional forests of northern Scandinavia and Finland. Previous efforts have probably underestimated N-fixation potential in boreal forests.

Nickel affects activity more than expression of hydrogenase protein in Frankia

The effects of nickel on hydrogen uptake and the post-translational processing of the large subunit of the hydrogenase protein in three Frankia strains (one isolated from an Alnus-Frankia symbiosis and two from Casuarina-Frankia associations) were investigated. All three strains responded to the addition of nickel with an increase in hydrogen uptake. Additional nickel did not affect nitrogenase activity, however evolved hydrogen was detected in Frankia KB5 in the absence of additional nickel, indicating that hydrogenase was not active. No increase in the processing rate of the hydrogenase large subunit was found with increasing nickel concentrations for any of the strains, indicating that the strategy for regulating hydrogenase in Frankia is different from that in other microorganisms.

Frankia KB5 possesses a hydrogenase immunologically related to membrane-bound

The immunological relationship of the hydrogenase in Frankia KB5 to hydrogenases in other microorganisms was investigated using antisera raised against holo-[NiFe]-hydrogenases isolated from Alcaligenes latus, Azotobacter vinelandii, Ralstonia eutropha, and the small and large hydrogenase subunits from Bradyrhizobium japonicum. The antisera raised against the A. latus, R. eutropha, and B. japonicum (large subunit) polypeptides were found to recognize two polypeptides, corresponding to the unprocessed and processed forms of the hydrogenase subunit in Frankia KB5. None of the antisera, including the antibodies produced against the small hydrogenase subunit isolated from B. japonicum, recognized any polypeptide related to the small hydrogenase subunit in Frankia KB5. An immunogold localization study of the intracellular distribution of hydrogenase in Frankia KB5, with the cryo-section technique, showed that labeling in the membrane of both hyphae and vesicles was positively correlated with hydrogenase activity.

DNase-resistant DNA in the extracellular and cell wall-associated fractions of Frankia strains R43 and CcI3

DNases were shown to be present in the extracellular fraction of Frankia strains R43 and CcI3. In spite of this, DNA was found in both the extracellular and cell wall fractions of these strains, and it was shown that extracellular DNA was resistant to the DNases secreted into the culture medium of both Frankia strains. Furthermore, Southern blot analysis under high stringency conditions revealed the chromosomal origin of the cell wall-adsorbed DNA (CW-DNA). Mobility gel band shift assays suggested that the extracellular DNA and the CW-DNA are engaged in complexes with other molecules, most likely proteins, which are probably responsible for the enzymatic resistance observed against extracellular DNase activities. In addition, it was shown that lysis of a small proportion of the cells in the exponential growth phase may account for the DNA being released into the supernatant and adsorbed to the cell wall.

Hydrogenase in Frankia KB5: expression of and relation to nitrogenase

The localization and expression of the hydrogenase in free-living Frankia KB5 was investigated immunologically and by monitoring activity, focusing on its relationships with nitrogenase and H2. Immunological studies revealed that the large subunit of the hydrogenase in Frankia KB5 was modified post-translationally, and transferred into the membrane after processing. The large subunit was constitutively expressed and no correlation was found between hydrogenase activity and synthesis. Although H2 was not needed for induction of hydrogenase synthesis, exogenously added H2 triggered hydrogen uptake in medium containing nitrogen, i.e., in the hyphae. A correlation between nitrogenase activity and hydrogen uptake was found in cultures grown in media without nitrogen, but interestingly the two enzymes showed no co-regulation.

A simple, rapid and non-destructive procedure to extract cell wall-associated proteins from Frankia

A simple cell fractionation procedure was developed to extract cell wall-associated proteins from the nitrogen-fixing actinomycete Frankia. The method was based on washing Frankia mycelia in 62.5 mM Tris-HCl (pH 6.8) buffer supplemented with 0.1% Triton X-100 as solubilizing agent. Cell wall-associated proteins were efficiently extracted in less than 10 min, recovering approximately 94.5+/-7.44 microg protein per extraction procedure from exponentially growing cells corresponding to 50 ml of culture. The amount of cell lysis occurring during the cell wall extraction was estimated to be 1.50+/-0.51%. Three peptidoglycan hydrolases with apparent molecular masses of 4.7, 12.1, and 17.8 kDa were detected by zymography in the cell wall-associated protein fraction. On the contrary, no cell wall lytic enzyme was detected in the cytoplasmic protein fraction. These results indicate that the present method enables a specific extraction of cell wall-associated proteins. Moreover, fluorescein isothiocyanate (FITC) labelling of the cell surface proteins showed an efficient removal of cell wall-associated proteins. Growth of the treated Frankia cells (i.e. cells from which the cell wall-associated proteins were removed) in semi-solid media suggested that these cells were still viable. This technique is of importance for functionality studies of cell wall-associated proteins, particularly for bacteria where traditional cell fractionation methods are difficult to be applied.

DNase Activities of the Extracellular, Cell Wall-Associated, and Cytoplasmic Protein Fractions of Frankia Strain R43

DNase activities in different protein fractions of Frankia strain R43 were studied. The extracellular and the cell wall-associated fractions revealed the presence of exo- and endonucleolytic enzymes, but none was detected in the cytoplasmic fraction. The strongest DNase hydrolysis was found in the extracellular fraction, in which six DNases were detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis.

Specificity and effectivity in nodulation by Frankia on southern hemisphere actinorhiza

Nodulation ability was tested for Frankia strains HFPCcI3 and EL1, and Frankia sources A.t. and G.a. from Allocasaurina torulosa and Gymnostoma australianum, respectively, on A. torulosa Miq., Casuarina cunninghamiana Miq., G. australianum L. Johnson and Elaeagnus triflora Roxb. It was shown that A. torulosa and C. cunninghamiana formed nodules only with the Frankia sources obtained from their own host plant, while E. triflora formed nodules with three of the four Frankia sources tested. All nodules formed were effectively fixing nitrogen. Specific nitrogenase activity was highest in E. triflora inoculated with the Frankia strain isolated from nodules of the same species. Identification of Frankia sources in the nodules was performed by use of PCR amplification of DNA with a random primer. PCR amplification of DNA isolated from nodules of G. australianum and E. triflora inoculated with Frankia strain EL1 revealed, when compared with DNA amplified from free living Frankia strain EL1, that there was only one Frankia strain causing the observed nodules.

Identification of Casuarina-Frankia strains by use of polymerase chain reaction (PCR) with arbitrary primers

Free-living N2-fixing Frankia strains isolated from Casuarina sp. were investigated for genomic polymorphism. We used six 10-mer oligonucleotides as single arbitrary primers (AP) for the polymerase chain reaction (PCR) in order to amplify random DNA fragments in the genome of free-living Frankia strains. Agarose-gels of the amplified genomic DNA revealed that two of the six arbitrary primers showed polymorphism in the eight different Frankia genomes. Analysis of the AP-PCR products showed 9 polymorphic bands ranging from 4.1-0.60 kb. We conclude that single arbitrary primers can be used to amplify genomic DNA, and that polymorphism can be detected between the amplification products of the different Frankia genomes.

Acetylene, Not Ethylene, Inactivates the Uptake Hydrogenase of Actinorhizal Nodules during Acetylene Reduction Assays

Acetylene reduction assays were shown to inactivate uptake hydrogenase activity to different extents in one Casuarina and two Alnus symbioses. Inactivation was found to be caused by C(2)H(2) and not by C(2)H(4). Acetylene completely inactivated the hydrogenase activity of intact root systems of Alnus incana inoculated with Frankia strain Avcl1 in 90 minutes, as shown by a drop in the relative efficiency of nitrogenase from 1.0 to 0.73. The hydrogenase of Frankia preparations (containing vesicles) and of cell-free extracts (not containing vesicles) from the same symbiosis was much more susceptible to acetylene inactivation. Cell-free extracts lost all hydrogenase activity after 5 minutes of exposure to acetylene. The hydrogenase activity of intact root systems of Casuarina obesa was less sensitive to acetylene than that of root systems of A. incana, since the relative efficiency of nitrogenase changed only from 1.0 to 0.95 over 90 minutes. Frankia preparations and cell-free extracts of C. obesa still retained hydrogenase activity after a 10 minute-exposure to acetylene.

Activities, occurrence, and localization of hydrogenase in free-living and symbiotic frankia

Symbiotic and free-living Frankia were investigated for correlation between hydrogenase activities (in vivo/in vitro assays) and for occurrence and localization of hydrogenase protein by Western blots and immuno-gold localization, respectively. Freshly prepared nodule homogenates from the symbiosis between Alnus incana and a local source of Frankia did not show any detectable in vivo or in vitro hydrogenase uptake activity, as also has been shown earlier. However, a free-living Frankia strain originally isolated from these nodules clearly showed both in vivo and in vitro hydrogenase activity, with the latter being approximately four times higher. Frankia strain Cpl1 showed hydrogen uptake activity both in symbiosis with Alnus incana and in a free-living state. Western blots on the different combinations of host plants and Frankia strains used in the present study revealed that all the Frankia sources contained a hydrogenase protein, even the local source where no in vivo or in vitro activity could be measured. The 72 kilodalton protein found in the symbiotic Frankia as well as in the free-living Frankia strains were immunologically related to the large subunit of a dimeric hydrogenase purified from Alcaligenes latus. Recognitions to polypeptides with molecular masses of about 41 and 19.5 kilodaltons were also observed in Frankia strain UGL011101 and in the local source of Frankia, respectively. Immunogold localization of the protein demonstrated that in both the symbiotic state and the free-living nitrogen-fixing Frankia, the protein is located in vesicles and in hyphae. The inability to measure any uptake hydrogenase activity is therefore not due to the absence of hydrogenase enzyme. However, the possibility of an inactive hydrogenase enzyme cannot be ruled out.

Acetylene reduction, H2 evolution and (15)N 2 fixation in the Alnus incana-Frankia symbiosis

Acetylene reduction, (15)N2 reduction and H2 evolution were measured in root systems of intact plants of grey alder (Alnus incana (L.) Moench) in symbiosis with Frankia. The ratios of C2H2: (15)N2 were compared with C2H2:N2 ratios calculated from C2H2 reduction and H2 evolution, and with C2H2:N2 ratios calculated from accumulated C2H4 production and nitrogen content. It was possible to calculate C2H2:N2 ratios from C2H2 reduction and H2 evolution because this source of Frankia did not show any hydrogenase activity. The ratios obtained using the different methods ranged from 2.72 to 4.42, but these values were not significantly different. It was also shown that enriched (15)N could be detected in the shoot after a 1-h incubation of the root-system. It is concluded that the measurement of H2 evolution in combination with C2H2 reduction represents a nondestructive assay for nitrogen fixation in a Frankia symbiosis which shows no detectable hydrogenase activity.

Biomass production and nitrogen utilization by Alnus incana when grown on N2 or NH 4 (+) made available at the same rate

A single clone of Alnus incana (L.) Moench was grown in a controlled-environment chamber. The plants were either inoculated with Frankia and fixed atmospheric nitrogen or were left uninoculated but received ammonium at the same rate as the first group fixed their nitrogen. Nitrogen fixation was calculated from frequenct measurements of acetylene reduction and hydrogen evolution. The diurnal variation of acetylene reduction was also taken into account. The relative efficiency of nitrogenase could be used in the calculations of fixed nitrogen since the Frankia used did not show any detectable hydrogenase activity. Alders fixing nitrogen developed more biomass, longer shoots, larger leaf areas and contained more nitrogen than alders receiving ammonium. In one experiment, almost all ammonium given to the non-nodulated alders was taken up and 15% of the nitrogen taken up was excreted. In the other experiment, 34% of the ammonium was left in the nutrient solution and 8% of the nitrogen taken up was excreted. Alders inoculated with Frankia did not excrete any detectable amount of nitrogen. It seems that the energy demand for nitrogen fixation is not so high that biomass production in alders is retarded. The symbiotic system of A. incana and Frankia seems to be more efficient in utilizing its nitrogen than non-symbiotic A. incana receiving ammonium.

Nitrogenase activity in response to restricted shoot growth in Alnus incana

In the Alnus–Frankia symbiosis the nitrogen-fixing root nodules are one of the sinks for carbon compounds newly formed in photosynthesis and exported from the leaves (source). The competition for assimilates between shoot tips and root nodules was studied by reducing shoot growth. Cloned plants of Alnus incana (L.) Moench were grown without combined nitrogen in a growth chamber. Shoot growth was inhibited by excision of all buds or by induced dormancy. The experiments showed an increased root biomass in the treated plants, indicating a changed source–sink balance. The treatments never caused an increased nitrogenase activity (C2H2-dependent C2H4 production); rather it was decreased. The nitrogenase activity was always correlated with leaf areas. It was also correlated with growth, which is shown by the similar nitrogen percentage in intact and treated plants.

Ammonium effects on function and structure of nitrogen-fixing root nodules of Alnus incana (L.) Moench

Cloned plants of Alnus incana (L.) Moench were inoculated and grown without combined nitrogen for seven weeks. The effects of ammonium on the function and structure of the root nodules were studied by adding 20 mM NH4Cl (20 mM KCl=control) for four days. Nitrogenase activity decreased to ca. 50% after one day and to less than 10% after two days in ammonium treated plants, but was unaffected in control plants. The results were similar at photon flux densities of 200 and 50 μmol m(-2) s(-1). At the higher light level the effect was concentration dependent between 2 and 20 mM NH4Cl. The recovery was slow, and more than 11 d were needed for plants treated with 20 mM ammonium to reach initial activity. The distribution of (14)C to the root nodules after assimilation of (14)CO2 by the plants was not changed by the ammonium treatment. Microscopical studies of root nodules showed high frequencies of endophyte vesicles being visually damaged in nodules from ammonium-treated plants, but not in nodules from control plants. When nitrogenase activity was restored, visually damaged vesicles were again few, whereas young developing vesicles were numerous. The slow recovery, the (14)C-translocation pattern, and the structural changes of the endophyte indicate a more complex mechanism of ammonium influence than simply a short-term reduction in supply of carbon compounds to the nodules.