Cyanobacterium Anabaena Azollae Research Articles

Effect of Water Sources on the Growth Performance and Chlorophyll Content of Azolla pinnata R.Br.


 
 
 Azolla pinnata R.Br. is an aquatic fern that grows on the surface of water bodies. The unique quality of A. pinnata is its symbiotic relationship with a prokaryotic cyanobacterium (Anabaena azollae), which confers a high rate of nitrogen fixation. It is important to find the growing conditions of Azolla in different water sources for its optimum biomass production for different usages such as biofertilizers, animal feeds, water purification and biofuel production. This preliminary study was conducted to investigate the effect of water sources on the growth performance (shoot biomass, root biomass, root length), and the chlorophyll content of Azolla. Presence of Anabaena in Azolla fronds was monitored by light microscope and number of filaments were counted per leaflet. The experiment utilized three types of water sources (tap water as control (T1), lake water (T2) and cattle manure mixed tap water (T3), in plastic buckets with 40 cm in diameter and 25 cm in height. Each treatment was triplicated in a completely randomized design and total biomass was collected weekly. Data were statistically analyzed using Minitab 17. The highest biomass of Azolla was obtained in T3 from the first week until 8th week and it was higher from T1 and T2. The highest chlorophyll content was obtained in T3 (6.4 SPAD value) showed a significant difference from T1 and T2 (p<0.05). The dry weight of roots and root length in T1 showed a significant difference from T2 and T3 (p<0.05). The highest root length was observed as 5 cm in T1 indicating that roots may be in search of nutrients and the lowest root length was observed as 0.8 cm in T3 with high nutrient concentrations in water. The highest number of Anabaena was observed in the leaflet of Azolla fronds in T3 which in turn increase N content in Azolla plants. It reveals that application of cattle manure in tap water significantly affects the plant biomass and the chlorophyll content of Azolla. Further studies are needed to conduct in large scale growing facilities with different nutrient concentrations of water sources to find sustainable and optimum growing conditions for Azolla and the nutrient concentrations of the plants.
 Keywords: Azolla, Chlorophyll, Growth performance, Water sources
 
 

Perspectives on the utilization of Azolla-Anabaena system as feed supplement

The nitrogen fixing aquatic pteridophyte Azolla is one of the fastest growing nitrogen-fixing plants and it is used as a potential source for high rate biomass production. Azolla has the ability to fix atmospheric nitrogen at cheaper and faster rates due to the presence of a symbiotic cyanobacterium Anabaena azollae. Therefore, the ability to fix atmospheric nitrogen is important from an agricultural perspective. However, Azolla is gaining popularity as feed supplement for cattle, poultry and fish. Further, the ease of cultivation and favourable nutrient composition make Azolla an important feed supplement. This review focuses on the perspectives of Azolla as feed supplement.

GC-MS Analysis of Bioactive Compounds and Hosttoxicity Studies of Azolla caroliniana Symbiotic with the Cyanobacterium Anabaena azollae

Abstract: Objective: The present research work was conducted to do the gas chromatography and mass spectrometry (GC-MS) analysis of the water fern, Azolla caroliniana symbiotic with the cyanobacterium Anabaena azollae, along with in vitro host toxicity testing to check its toxicity level. Materials and methods: The GC-MS analysis of the methanol extract of A. caroliniana was carried out using a GC-MS instrument and in vitro host toxicity testing of A. caroliniana extract was carried out with cultured lymphocytes from human umbilical cord blood. Results: It was evident that only one phytochemical, 3-o-methyld- glucose with retention time 16.581 min and a peak area of 91.89% as the major phytochemical was present in methanolic extract of the fern, while the rest 7 of the total 8 chemicals namely (with peak area values), ‘2-butanone, 3-methoxy-3-methyl’ (0.865%), ‘2,2-dimethyl propionic acid, cyclopentyl ester’ (0.670%), ‘butane, 1-bromo- 2-methyl’ (0.398%), ‘2-hexen-1-ol,2-ethyl’ (0.269%), ‘5-hydroxy-2,2-dimethyl hexan- 3-one’ (0.212%), ‘phthalic acid, ethyl pentyl ester’ (0.21%), ‘pentanoic acid, 2-methyl’ (0.182%), were present in minor quantities. Host toxicity testing was done with in vitro cultured lymphocytes from human umbilical cord blood. The LC25 values were 870.96 and 691.83 mg/L with the trypan blue and acridine orange/ethidium bromide staining, respectively by methanolic extract of A. caroliniana in cellular toxicity experiments, against the minimum inhibitory concentration values of 300 mg/L extract. During the assessment of nuclear toxicity, no comet was found in the cells grown with 0 to 1000 mg/L of the extract. Conclusion: The extract had neither cellular nor nuclear toxicity to cultured human lymphocytes. Key words: Azolla Caroliniana, Fern, Gc-Ms Analysis, 3-O-Methyl-D-Glucose, Host Toxicity Testing, In Vitro Cultured Lymphocytes.

Aquatic plant Azolla as the universal feedstock for biofuel production.

BackgroundThe quest for sustainable production of renewable and cheap biofuels has triggered an intensive search for domestication of the next generation of bioenergy crops. Aquatic plants which can rapidly colonize wetlands are attracting attention because of their ability to grow in wastewaters and produce large amounts of biomass. Representatives of Azolla species are some of the fastest growing plants, producing substantial biomass when growing in contaminated water and natural ecosystems. Together with their evolutional symbiont, the cyanobacterium Anabaena azollae, Azolla biomass has a unique chemical composition accumulating in each leaf including three major types of bioenergy molecules: cellulose/hemicellulose, starch and lipids, resembling combinations of terrestrial bioenergy crops and microalgae.ResultsThe growth of Azolla filiculoides in synthetic wastewater led up to 25, 69, 24 and 40 % reduction of NH4–N, NO3–N, PO4–P and selenium, respectively, after 5 days of treatment. This led to a 2.6-fold reduction in toxicity of the treated wastewater to shrimps, common inhabitants of wetlands. Two Azolla species, Azolla filiculoides and Azolla pinnata, were used as feedstock for the production of a range of functional hydrocarbons through hydrothermal liquefaction, bio-hydrogen and bio-ethanol. Given the high annual productivity of Azolla, hydrothermal liquefaction can lead to the theoretical production of 20.2 t/ha-year of bio-oil and 48 t/ha-year of bio-char. The ethanol production from Azolla filiculoides, 11.7 × 103 L/ha-year, is close to that from corn stover (13.3 × 103 L/ha-year), but higher than from miscanthus (2.3 × 103 L/ha-year) and woody plants, such as willow (0.3 × 103 L/ha-year) and poplar (1.3 × 103 L/ha-year). With a high C/N ratio, fermentation of Azolla biomass generates 2.2 mol/mol glucose/xylose of hydrogen, making this species a competitive feedstock for hydrogen production compared with other bioenergy crops.ConclusionsThe high productivity, the ability to grow on wastewaters and unique chemical composition make Azolla species the most attractive, sustainable and universal feedstock for low cost, low energy demanding, near zero maintenance system for the production of a wide spectrum of renewable biofuels.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0628-5) contains supplementary material, which is available to authorized users.

The aquatic fern Azolla as a natural plant-factory for ammonia removal from fish-breeding fresh wastewater.

This study has investigated the potential of an Azolla-Anabaena symbiosis, a marriage between the cyanobacterium Anabaena azollae and the aquatic fern (Azolla), to remove ammonia from freshwater fish breeding areas. Experiments were carried out under artificial light of 20, 70, and 140μmolm(-2) s(-1). We investigated three different water temperatures for the growing Azolla, ranging from sub-optimal to optimal temperatures (15, 22, and 28°C). The capability of Azolla to remove ammonia from wastewater was demonstrated, and the highest ammonia concentration tolerated by the symbiosis between Azolla-anabaena without any toxic effect on the aquatic ferns was ascertained. The shortest time taken to remove ammonia from wastes, 2.5cm deep and at 28°C, was 40min. The ammonia removal rate (A RR) was both light and temperature dependent and the highest rate (6.394h(-1)) was attained at light intensity of 140μmolm(-2)s(-1) and at a temperature of 28°C; the lowest (0.947h(-1)) was achieved at 20μmolm(-2) s(-1) and 15°C. The depth of the fish-wastewater pool also affected the A RR with the relation between A RR and the depth being a hyperbolic function.

Advancements in the Utilization of Azolla-anabaena System in Relation to Sustainable Agricultural Practices

The nitrogen fixing aquatic pteridophyte Azolla has the ability to fix atmospheric nitrogen at cheaper and faster rates due to the presence of a symbiotic cyanobacterium Anabaena azollae. Because of this property it has been exploited widely as biofertilizer for rice plants. In addition to this it has several other uses such as food, feed, biogas producer and hyperaccumulator of heavy metals etc. Because of the multifaceted uses the promotion and use of Azolla-Anabaena system would be ideal and environment friendly in sustainable agriculture. This article provides a brief account of the importance as well as developments in the utilization of Azolla-Anabaena system in agriculture and allied sectors.

Effects of Seasonal Changes on Pigment Composition ofAzolla filiculoidesLam.

Abstract Azolla is a floating fern, which contains the nitrogen-fixing cyanobacterium Anabaena azollae in the dorsal lobe cavity of the leaves. This study investigated the effects of seasonal changes on the pigment composition of Azolla filiculoides in a small pond located in Istanbul, Turkey. Sampling was conducted in March, April, May, October, November, December 2007. The average total chlorophyll and carotenoid content of the leaves was almost a half fold lower in March-April-May than in October-November-December. For late winter–spring, while the average chlorophyll a/b ratio of the leaves was 2.6, for autumn - early winter it was 5.5. In March, leaf dimensions reduced, whereas the anthocyanin accumulation in the leaves increased. In May, together with the increasing temperature values, while the leaf dimensions and biomass increased, the leaves returned to green. From October to November, both leaf dimensions and amount of anthocyanin in the leaves reduced. Results showed that the probable growth se...

CHARACTERIZATION OF ANABAENA AZOLLAE ISOLATED FROM AZOLLA PINNATA

A symbiotically associated cyanobacterium (Anabaena azollae) was isolated from Azolla pinnata and cultured under a free-living state. It is characterized by filamentous brown to olive in color culture, its vegetative cells are cylindrical and their diameters ranged from 8 to 9µm width and from 5 to 6 µm length. Heterocysts were found to be internal and terminal in the filament, its shape is spherical and its diameters ranged from 9 to 9.5 µm width and from 9 to 9.5 µm length. Akintes are present with cylindrical shape, with diameters of 9-10 µm width and 6-8 µm length. Nitrogenase activity of Anabaena azollae increased gradually from 0.1786 to 4.7992 μ mole C2H4 g soil/hr along 4 weeks. The strain showed high efficacy in suppressing the fungal mycelial growth of either Fusarium oxysporum or Alternaria alternate by 100 %.

Azolla-Anabaenaas a Biofertilizer for Rice Paddy Fields in the Po Valley, a Temperate Rice Area in Northern Italy

Azollais a floating pteridophyte, which contains as endosymbiont the nitrogen-fixing cyanobacteriumAnabaena azollae(Nostocaceae family). Widely cultivated in the Asian regions,Azollais either incorporated into the soil before rice transplanting or grown as a dual crop along with rice. To examine the feasibility of its use in flooded rice fields sited in the Temperate European Areas, we carried out a series of experiments in PVC tanks during 2000–2002 in Po Valley (northern Italy) conditions, to study the growth-development dynamics and the resistance/tolerance to low temperatures and to commonly used herbicides of several differentAzollastrains. Three out of five strains tested survived the winter, with an increase in biomass from March to May producing approximately 30–40 kg of nitrogen. One of these strains, named “Milan”, emerged as the most resistant to herbicide and the most productive. Of the herbicides tested, Propanil permitted the survival of growingAzolla.

Cyanobacterial biofertilizers in rice agriculture

Floodwater and the surface of soil provide the sites for aerobic phototrophic nitrogen (N) fixation by free-living cyanobacteria and theAzolla-Anabaena symbiotic N2-fixing complex. Free-living cyanobacteria, the majority of which are heterocystous and nitrogen fixing, contribute an average of 20–30 kg N ha-1, whereas the value is up to 600 kg ha-1 for theAzollaAnabaena system (the most beneficial cyanobacterial symbiosis from an agronomic point of view). Synthesis and excretion of organic/growth-promoting substances by the cyanobacteria are also on record. During the last two or three decades a large number of studies have been published on the various important fundamental and applied aspects of both kinds of cyanobacterial biofertilizers (the free-living cyanobacteria and the cyanobacteriumAnabaena azollae in symbiotic association with the water fernAzolla), which include strain identification, isolation, purification, and culture; laboratory analyses of their N2-fixing activity and related physiology, biochemistry, and energetics; and identification of the structure and regulation of nitrogenfixing (nif) genes and nitrogenase enzyme. The symbiotic biology of theAzolla-Anabaena mutualistic N2-fixing complex has been clarified. In free-living cyanobacterial strains, improvement through mutagenesis with respect to constitutive N2 fixation and resistance to the noncongenial agronomic factors has been achieved. By preliminary meristem mutagenesis inAzolla, reduced phosphate dependence was achieved, as were temperature tolerance and significant sporulation/spore germination under controlled conditions. Mass-production biofertilizer technology of free-living and symbiotic (Azolla-Anabaena) cyanobacteria was studied, as were the interacting and agronomic effects of both kinds of cyanobacterial biofertilizer with rice, improving the economics of rice cultivation with the cyanobacterial biofertilizers. Recent results indicate a strong potential for cyanobacterial biofertilizer technology in rice-growing countries, which opens up a vast area of more concerted basic, applied, and extension work in the future to make these self-renewable natural nitrogen resources even more promising at the field level in order to help reduce the requirement for inorganic N to the bare minimum, if not to zero.

351 Nitrogen-fixing Water Fern Azolla as Biofertilizer for Hot Pepper (Capsicum chinense var. Scotch Bonnet)

Scotch Bonnet pepper is a valuable commodity for Jamaica and the Caribbean, both for local consumption and for export because of its unique flavor and pungency. It is a valuable cash crop for small farmers who supply most of the fruit needed for processing and export. Azolla is a small water fern that grows on the surface of water bodies or on moist soil. Due to the presence of the nitrogen-fixing cyanobacterium Anabaena azollae, it fixes molecular nitrogen. This fern is used as biofertilizer for rice in millions of hectares in Asia. In the present work, experiments were carried out to determine the suitability and usefulness of both fresh and dried Azolla as biofertilizer for Scotch Bonnet pepper. A control without any fertilizer and a fertilizer control with 100 kg N/ha, supplied as ammonium sulfate, were used in 2-m2 plots, with three replicates for each treatment. Fertilizer was supplied in three split doses. Fresh Azolla was spread at the base of each plant and the soil was kept moist for the duration of the study. Dry Azolla was spread like a mulch around the base of the plant and used as a split treatment similar to inorganic fertilizer. Both the fresh and dry Azolla increased the marketable fruit yield over the control without fertilizer. Dry Azolla resulted in a similar yield as the fertilizer treatment [80%] while the fresh Azolla had a 60% increase in the yield over the control. In addition, dry Azolla resulted in early anthesis by 3 days over the fertilizer control. The dry weights of the whole shoot also showed increases similar to fruit yield. The dry Azolla also helped to improve the soil conditions and retained moisture for long periods. The results suggest that dry Azolla can be successfully substituted for chemical fertilizer for pepper. The cost of preparing Azolla to be used as fertilizer is calculated to be about 10% to 15% of the cost of chemical fertilizer for small farmers.

Mutational analysis of Asp51 of Anabaena azollae glutamine synthetase. D51E mutation confers resistance to the active site inhibitors L-methionine-DL-sulfoximine and phosphinothricin.

The role of Asp51 in the catalytic activity of glutamine synthetase from the cyanobacterium Anabaena azollae has been analyzed. Five mutant enzymes, D51S, D51A, D51E, D51N and D51R, were constructed by site-directed mutagenesis and characterized. Asp51 appears to participate in the binding of ammonium ion, as affinity for this substrate was affected in all cases, although it varied according to the charge and/or size of the amino-acid residue, decreasing in the order Glu > Asn > Ser > Ala. The replacement of Asp51 by Glu (D51E) conferred besides a high resistance to the herbicides L-methionine-DL-sulfoximine and phosphinothricin, as a result of a decreased phosphorylation ability.

Characterization of akinete differentiation in the cyanobacterium Anabaena azollae

Differentiation of akinetes was investigated in the filamentous cyanobacterium Anabaena azollae Stras. In this organism all pre-existing vegetative cells are capable of developing into akinetes. Standard sporulation medium (SSM) was used to synchronously induce the formation of akinetes, while cultures in Allen and Arnon (AA/8) medium were used as controls.This paper describes the changes in photosynthetic pigments and total soluble proteins in these cultures over a 25-day period encompassing akinete differentiation. Heterocyst frequencies and nitrogenase activity were also monitored during the same period in both media. SDS-PAGE results indicated that specific proteins were synthesized in a manner correlated with akinete differentiation. The results demonstrate that in cultures undergoing akinete development, some of the photosynthetic pigments are maintained, nitrogen-fixation and heterocyst differentiation are suppressed, and the cells synthesize a variety of specific proteins.

Azolla: An efficient N2-fixing association with three components

Abstract Bacterial population is found together with the cyanobacterium Anabaena azollae in the leaf cavities and the sporocarps of Azolla. Different Arthrobacter species have been invariably isolated from the leaf cavities and sporocarps of several fern species. About the role of the bacteria in the association, it is probable that the bacteria affect the carbon and nitrogen metabolism of the cavity by competing with the Anabaena for the nutrients and in the meantime it is likely that their high respiratory activity favours the establishment of a microaerobic environment and consequently the nitrogenase activity. Furthermore Arthrobacter may contribute to the production of the mucilage present in the algal packets by excreting extracellular polysaccharides, which components can be involved in lectin binding with Azolla and Anabaena. Finally the IAA formation by Arthrobacter may influence the hormonal balance during the establishment of the association.

Effect of Benlate and Rhizoctonia interactions on the growth, chlorophyll contents and nitrogen fixation in three species of Azolla

Azolla is an aquatic fern that fixes atmospheric nitrogen in symbiotic association with the cyanobacterium Anabaena azollae. Azolla fronds are commonly affected by a soil-borne pathogen, namely Rhizoctonia solani. Benlate, a systemic fungicide, was used for treating three species of Azolla with a view to assessing its effect on growth, chlorophyll synthesis and nitrogen-fixing potential besides checking the Rhizoctonia solani infection. Benlate at 2.5 p.p.m. induced the growth of Azolla microphylla – BR–GI, Azolla caroliniana – WT–V and Azolla sp. – ST–SI. The growth rate induction in Azolla sp. – ST–SI due to Benlate treatment was significant. The culture Azolla sp. – ST–SI showed maximum nitrogenase activity due to Benlate treatment, followed by A. microphylla – BR–GI. A. caroliniana – WT–V and Azolla sp. – ST–SI, when treated with Benlate, have shown higher chlorophyll. Benlate treatment reduced the nitrogen content in A. microphylla – BR-GI and Azolla sp. – ST–SI, while carbon content was not affected much. Azolla is ’n watervaring wat atmosferiese stikstof bind in simbiotiese assosiasie met die sianobakterie Anabaena azollae. Azolla blare word algemeen aangetas deur die grondpatogeen Rhizoctonia solani. Benlate, ’n sistemiese swamdoder, is gebruik om drie Azolla spesies te behandel, nie net om die Rhizoctonia solani infeksie te stuit nie, maar ook om die uitwerking daarvan op die groei, chlorofilsintese en stikstofbindingspotensiaal te bepaal. Benlate, teen 2.5 d.p.m., het die groei van Azolla microphylla – BR–GI, Azolla caroliniana – WT–V en Azolla sp. – ST–SI geïnduseer. Die groeitempo-induksie by Azolla sp. – ST–SI as gevolg van Benlate-behandeling was betekenisvol. Die kultuur Azolla sp. – ST–SI het maksimum nitrogenase-aktiwiteit as gevolg van Benlate-behandeling getoon, gevolg deur A. microphylla – BR–GI. Wanneer met Benlate behandel, het A. caroliniana – WT–V en Azolla sp. – ST–SI hoër chlorofil getoon. Benlate-behandeling het die stikstofinhoud van A. microphylla – BR–GI en Azolla sp. – ST–SI verminder, terwyl die koolstofinhoud nie veel beïnvloed is nie.

Indigenous plasmids in Anabaena azollae: their taxonomic distribution and existence of regions of homology with symbiotic genes of Rhizobium

The method of horizontal agarose gel electrophoresis was used to demonstrate the presence of indigenous plasmid DNAs in different isolates of the symbiotic cyanobacterium Anabaena azollae. All isolates extracted from seven distinct species of the host fern Azolla were found to possess one to three cryptic plasmids ranging in sizes from 35 to 100 MDa (million daltons). Anabaenas isolated from Azolla caroliniana, Az. nilotica, and Az. pinnata species contained a single plasmid band of molecular mass approximately 60 MDa, whereas other endosymbiotic cyanobacteria extracted from Azolla filiculoides, Az. rubra, Az. mexicana, and Az. microphylla were shown to possess two or three covalently closed circular (CCC) DNAs. Cloned DNA fragments derived from the plasmid sequences of two different An. azollae isolates were used as hybridization probes. Hybridization data indicated that these symbiotic cyanobacteria possess different but related plasmid species and that it is possible to construct specific plasmid DNA probes capable of distinguishing among several strains of the symbiotic anabaenas. Several heterologous DNA probes, including Rhizobium symbiotic genes, were used to seek homologous sequences on the An. azollae plasmids. DNA sequences homologous to the nod box and nodMN genes were present on the Anabaena plasmids. Moreover, homology of a key Rhizobium exopolysaccharide (exoY) gene to the An. azollae CCC DNAs was detected. In addition, the introduction of the An. azollae plasmid clone into Rhizobium Exo− mutant (exoY) resulted in the Exo+ transconjugants. Those findings suggest that some of the An. azollae plasmids may play a role in symbiotic interactions with Azolla fem. Key words: Anabaena azollae, Azolla, symbiosis, cyanobacterium, plasmids.

Isolation of Agrobacterium sp., strain from the Azolla leaf cavity

We have isolated a bacterial strain from surface sterilized fronds of the aquatic fern Azolla filiculoides and infer that it occurs in leaf cavities, along with the nitrogen-fixing cyanobacterium Anabaena azollae. This strain grew slowly on rich media, appeared to be Gram-negative, and was identified using a bacteriological multitest system as Agrobacterium sp. This strain, designated AFSR-1, could grow in the presence of 400 ppm of ammonium sulphate. DNA/DNA hydrodization analysis showed that a 16 S ribosomal RNA gene is located in the AFSR-1 strain on an identical DNA restriction fragment as in a strain of Agrobacterium tumefaciens. In addition, it was found that strain AFSR-1 contained DNA regions homologous to the modulation genes nodABC and nodL of Rhizobium trifolii, AFSR-1 contains a cryptic plasmid, and the genetic transfer of a broad-host-range plasmid pLAFR3 to strain AFSR-1 was achieved.

Isolation ofAgrobacteriumsp., strain from theAzollaleaf cavity

We have isolated a bacterial strain from surface sterilized fronds of the aquatic fern Azolla filiculoides and infer that it occurs in leaf cavities, along with the nitrogen-fixing cyanobacterium Anabaena azollae. This strain grew slowly on rich media, appeared to be Gram-negative, and was identified using a bacteriological multitest system as Agrobacterium sp. This strain, designated AFSR-1, could grow in the presence of 400 ppm of ammonium sulphate. DNA/DNA hydrodization analysis showed that a 16 S ribosomal RNA gene is located in the AFSR-1 strain on an identical DNA restriction fragment as in a strain of Agrobacterium tumefaciens. In addition, it was found that strain AFSR-1 contained DNA regions homologous to the modulation genes nodABC and nodL of Rhizobium trifolii, AFSR-1 contains a cryptic plasmid, and the genetic transfer of a broad-host-range plasmid pLAFR3 to strain AFSR-1 was achieved.

Regulation of nitrogen fixation in diazotrophs: the regulatorynifA gene and its characteristics

Biological nitrogen fixation is an important link in the nitrogen cycle. The ability to convert atmospheric nitrogen to metabolically usable compounds is confined to a few classes of bacteria and blue-green algae. Nitrogen-fixing organisms can be divided into two groups, (i) The free-living species that fix nitrogen for their own purpose, e.g. Klebsiella pneumoniae and Azotobacter vinelandii. (ii) The species that depend on an intimate association with plants, e.g. the cyanobacterium Anabaena azollae with the waterfern Azolla, or on intracellular symbiosis, e.g. the bacterial genera Rhizobium, Bradyrhizobium and Azorhizobium with various, specific leguminous host plants, and the actinomycete Frankia with alders. Nitrogen fixation by Rhizobium species in symbiosis with members of the plant family Leguminosae [amongst others: pea, ( Pisum sativum L.), soybean ( Glycine max L.) and alfalfa ( Medicago sativa L.)] is of great importance to agriculture. The interaction of bacteria and plants is a very complicated multistep process that involves gene products from both symbiotic partners. Rhizobium bacteria interact with their specific host plants, which results in the formation of newly developed anatomical structures on the main and lateral roots of the plants, the root nodules. In some cases, e.g. Azorhizobium caulinodans, with its host plant Sesbania rostrata, nodules are also formed on the stem. In the nodules some cells contain bacteroids, specialized forms of the bacterium that are capable of fixing nitrogen by means of the oxygen-sensitive enzyme, nitrogenase. This enzyme complex, which consists of three different polypeptides, fixes atmospheric nitrogen into ammonia. The symbiotic bacteria-plant interaction is marked by the symbiosis-specific expression of both bacterial and plant genes. In this review we will summarize and discuss data specifically concerning the regulation of the genes that are expressed in nitrogen-fixing bacteria. We will focus upon two bacterial species that are exemplary: the facultative anearobic K. pneumoniae and the obligate aerobe Rhizobium meliloti, the symbiont of alfalfa ( M. sativa).

Tunicamycin suppresses differentiation and stimulates dedifferentiation of heterocysts in the cyanobacteriumAnabaena azollae Stras

The effect of tunicamycin (TM), a specific inhibitor of glycosylation of proteins, on heterocyst differentiation inAnabaena azollae Stras. was investigated. Heterocysts were developed in the presence of TM up to a concentration of 0.2 μg ml−1, whereas at higher concentrations differentiation proceeded only up to the proheterocyst stage. Analysis of lipids by thinlayer chromatography showed that the glycolipid that is specific for the laminated layer of mature heterocysts was synthesized even in the cultures where the differentiation had proceeded only up to the early proheterocyst stage (i.e., at>0.2 μg TM ml−1). Further, deposition of the glycolipid-containing laminated layer in the envelope of the heterocysts differentiated in the presence of TM (i.e., at ≤0.2 μg ml−1) was incohesive as observed at the ultrastructural level. These findings clearly suggest that the process leading to the transportation of the heterocyst-specific glycolipid and its deposition as a laminated layer are affected by TM treatment. Because of the reported highly selective mode of action of TM, our results implicate a role for protein glycosylation in the process of heterocyst development and maturation.