Comparative analysis of cyanobacteria in the rhizosphere and as endosymbionts of cycads in drought-affected soils

Does the diversity of cyanobacteria in the cycad rhizosphere relate to the cyanobiont species found in the coralloid roots of these ancient plants? The aim of this study was to identify the diversity of soil cyanobacteria occurring in the immediate vicinity of 22 colonized coralloid roots belonging to members of the cycad genera: Macrozamia, Lepidozamia, Bowenia and Cycas. The majority of coralloid roots were sampled at depths >?10?cm below the soil surface. A total of 32 cyanobacterial isolates were cultured and their 16S rRNA gene partially sequenced. Phylogenetic analysis revealed nine operational taxonomic units of soil cyanobacteria comprising 30 Nostoc spp., a Tolypothrix sp. and a Leptolyngbya sp. Microscopy indicated that all isolates were unialgal and confirmed their genus identity. Rhizospheric diversity was compared to existing data on cyanobionts isolated at the same time from the cycad coralloid root. The same isolate was present in both the cycad coralloid root and rhizosphere at only six sites. Phylogenetic evidence indicates that most rhizosphere isolates were distinct from root cyanobionts. This weak relationship between the soil cyanobacteria and cycad cyanobionts might indicate that changes in the soil community composition are due to environmental factors.     

Genetic diversity of symbiotic cyanobacteria in Cycas revoluta (Cycadaceae)

The diversity of cyanobacterial species within the coralloid roots of an individual and populations of Cycas revoluta was investigated based on 16S rRNA gene sequences. Sixty-six coralloid roots were collected from nine natural populations of cycads on Kyushu and the Ryukyu Islands, covering the entire distribution range of the species. Approximately 400?bp of the 5'-end of 16S rRNA genes was amplified, and each was identified by denaturing gradient gel electrophoresis. Most coralloid roots harbored only one cyanobiont, Nostoc, whereas some contained two or three, representing cyanobiont diversity within a single coralloid root isolated from a natural habitat. Genotypes of Nostoc within a natural population were occasionally highly diverged and lacked DNA sequence similarity, implying genetic divergence of Nostoc. On the other hand, Nostoc genotypes showed no phylogeographic structure across the distribution range, while host cycads exhibited distinct north-south differentiation. Cycads may exist in symbiosis with either single or multiple Nostoc strains in natural soil habitats.     

Associative cyanobacteria isolated from the roots of epiphytic orchids

Associative cyanobacteria were isolated from the rhizoplane and velamen of the aerial roots of the epiphytic orchids Acampe papillosa, Phalaenopsis amabilis, and Dendrobium moschatum and from the substrate roots of Acampe papillosa and Dendrobium moschatum. Cyanobacteria were isolated on complete and nitrogen-free variants of BG-11 medium. On all media and in all samples, cyanobacteria of the genus Nostoc predominated. Nostoc, Anabaena, and Calothrix were isolated from the surface of the A. papillosa aerial roots, whereas the isolates from the substrate roots were Nostoc, Oscillatoria, and representatives of the LPP-group (Lyngbia, Phormidium, and Plectonema, incapable of nitrogen fixation). On the D. moschatum substrate roots, Nostoc and LPP-group representatives were also found, as well as Fischerella. On the aerial roots of P. amabilis and D. phalaenopsis grown in a greenhouse simulating the climate of moist tropical forest, cyanobacteria were represented by Nostoc, LPP-group, and Scytonema in the D. phalaenopsis and by Nostoc, Scytonema, Calothrix, Spirulina, Oscillatoria, and the LPP-group in P. amabilis. For D. moschatum, the spectra of cyanobacteria populating the substrate root zhizophane and the substrate (pine bark) were compared. In the parenchyma of the aerial roots of P. amabilis, fungal hyphae and/or their half-degraded remains were detected, which testifies to the presence of mycorrhizal fungi this plant. This phenomenon is attributed to the presence of a sheath formed by cyanobacteria and serving as a substrate for fungi.     

Isolation and characterization of hydrogen-oxidizing bacteria induced following exposure of soil to hydrogen gas and their impact on plant growth

In many legumes, the nitrogen fixing root nodules produce H2 gas that diffuses into soil. It has been demonstrated that such exposure of soil to H2 can promote plant growth. To assess whether this may be due to H2-oxidizing microorganisms, bacteria were isolated from soil treated with H2 under laboratory conditions and from soils collected adjacent to H2 producing soybean nodules. Nineteen isolates of H2-oxidizing bacteria were obtained and all exhibited a half-saturation coefficient (Ks) for H2 of about 1 ml l(-1). The isolates were identified as Variovorax paradoxus, Flavobacterium johnsoniae and Burkholderia spp. using conventional microbiological tests and 16S rRNA gene sequence analysis. Seventeen of the isolates enhanced (57-254%) root elongation of spring wheat seedlings. Using an Arabidopsis thaliana bioassay, plant biomass was increased by 11-27% when inoculated by one of four isolates of V. paradoxus or one isolate of Burkholderia that were selected for evaluation. The isolates of V. paradoxus found in both H2-treated soil and in soil adjacent to soybean nodules had the greatest impact on plant growth. The results are consistent with the hypothesis that H2-oxidizing bacteria in soils have plant growth promoting properties.     

Paracrystalline inclusions in various isolates of the blue-green bacteria Nostoc and Anabaena.

A number of different crystalline inclusions were observed in various isolates of Anabaena and Nostoc. Membrane-limited crystalline bodies were observed in 7 of 20 isolates of Anabaena and 19 of 29 isolates of Nostoc. These are spherical, single membrane-limited bodies from 0.6 to 0.1 micron in diameter. In most of the isolates they contained needle-like crystals 20 A in thickness and up to 80 nm in length. In 9 of the isolates the inclusions contained granular and fibrillar material. The number of bodies per cell varied in the different isolates from only a few, observed in many sections, up to 5 in a single section of A. subtropica (B1618). Crystalloids were observed in the cytoplasm of Anabaena sp. (1551), N. calcicola (B382), Nostoc sp. (588), and N. punctiforme (1629). In Anabaena sp. (1551) the roughly cuboidal inclusions 0.6 micron in diameter were composed of 100 A thick osmiophilic striations spaced to produce a 150 A periodicity. In Nostoc sp. (588) the elongate, 0.1 micron by 2.5 micron, crystalloids were composed of 100 A thick osmiophilic striations spaced to produce a 200 A periodicity. N. punctiforme (1629) and N. calciola (B382) contained intrathylakoidal crystalloids which consisted of short curved segments with 100 A thick osmiophilic striations producing a 200 A periodicity. Granular areas were observed in 2 isolates of Anabaena and 5 of Nostoc. These bodies found in various locations in the cells, were interpreted to be elongate structures 0.2 micron thick, 1.2 micron long and about 5 micron in depth. These inclusions were composed of 15 nm diameter granules which in some section planes appeared in rows spaced 20 nm apart. Spherical bodies up to 0.7 micron in diameter and of medium electron density were observed in 4 isolates of Anabaena and 2 of Nostoc. Convoluted inclusions were found in N. calcicola (B382) and Anabaena sp. (1551). These roughly spherical bodies up to 0.8 micron in diameter contain lighter swirled areas.     

Comparison between Rosellinia necatrix isolates from soil and diseased roots in terms of hypovirulence

The white root rot fungus, Rosellinia necatrix, is a devastating soil-borne pathogen of many plant species. Biocontrol with the hypovirulence factor is promising, but disease symptoms, signs or culture morphology of the pathogen cannot be reliably used as markers for hypovirulence in this fungus. We attempted to obtain hypovirulent isolates from soil rather than from diseased roots, based on the hypothesis that hypovirulent isolates were more likely to persist in soil as saprobes. Sixteen isolates, belonging to eight mycelial compatibility groups (MCGs), were obtained from soil in two active and one abandoned Japanese pear orchards. Comparison of these isolates based on clonality revealed that six MCGs were commonly recovered from both diseased roots and soil and two MCGs exclusively from soil. No MCG was found in more than one orchard. With two exceptions, isolates within the same MCG were similar in virulence, competitive saprophytic ability (CSA) and mycelial growth rate whether or not they carried dsRNA. The two exceptional isolates recovered from soil had multiple dsRNA segments that caused hypovirulence, weakened CSA and restricted mycelial growth on nutrient-rich media. They belonged to different MCGs, each including dsRNA-free isolates. Isolates from soil contained various dsRNAs (44%), including the hypovirulence factor, more frequently than isolates from diseased roots in the same fields (25%), which is much higher than the proportion of isolates with dsRNA from diseased roots (19%) in a total of 424 isolates from Japan examined so far. These results suggest that isolation of R. necatrix from soil is an effective method to obtain isolates with dsRNAs, including the hypovirulence factor.     

Influence of Two Plant Species (Flax and Tomato) on the Distribution of Nitrogen Dissimilative Abilities within Fluorescent Pseudomonas spp

The distribution of nitrogen-dissimilative abilities among 317 isolates of fluorescent pseudomonads was studied. These strains were isolated from an uncultivated soil and from the rhizosphere, rhizoplane, and root tissue of two plant species (flax and tomato) cultivated on this same soil. The isolates were distributed into two species, Pseudomonas fluorescens (45.1%) and Pseudomonas putida (40.4%), plus an intermediate type (14.5%). P. fluorescens was the species with the greatest proportion of isolates in the root compartments and the greatest proportion of dissimilatory and denitrifying strains. According to their ability to dissimilate nitrogen, the isolates have been distributed into nondissimilatory and dissimilatory strains, nitrate reducers and true denitrifiers with or without N(inf2)O reductase. The proportion of dissimilatory isolates was significantly enhanced in the compartments affected by flax and tomato roots (55% in uncultivated soil and 90 and 82% in the root tissue of flax and tomato, respectively). Among these strains, the proportion of denitrifiers gradually and significantly increased in the root vicinity of tomato (44, 68, 75, and 94% in uncultivated soil, rhizosphere, rhizoplane, and root tissue, respectively) and was higher in the flax rhizoplane (66%) than in the uncultivated soil. A higher proportion of N(inf2)O reducers was also found in the root compartments. This result was particularly clear for tomato. It is hypothesized that denitrification could be a selective advantage for the denitrifiers in the root environment and that this process could contribute to modify the specific composition of the bacterial communities in the rhizosphere.     

Fate of nitrogen applied as Azolla and blue-green algae (Cyanobacteria) in waterlogged rice soils—a15N tracer study

Summary ¹⁵N tracer was used to detect the extent to which nitrogen of appliedAzolla caroliniana, Anabaena variabilis andNostoc muscorum was available for assimilation by the growing rice plants in pots under 4 cm flood water for 60 days. The rate of release of nitrogen from the above biofertilizers, the amount of nitrogen remaining in the soils and the amount that was lost from the soils during this period were also examined. Previously¹⁵N-labelled biomass of Azolla, Anabaena and Nostoc to provide 40 mg N was mixed thoroughly with 0.5 kg silt loam Bangladesh soil (Sonatola series) in each of three pots used for a single treatment. Each pot received four 16 days old IR8 rice seedlings. A parallet set of experiments was conducted without rice plants.It was found that nitrogen uptake in the rice plants was increased by 91, 176 and 215% on using Azolla, Anabaena and Nostoc which resulted in increased total dry matter yields (shoot plus root) of 74, 105 and 125%, respectively. Of the total¹⁵N applied at the start, 26, 49 and 53% was released from Azolla, Anabaena and Nostoc; about 7, 14 and 13% was lost by denitrification and 74, 51 and 47% remained in the soils as the undecomposed part of the biofertilizers, respeciively, after 60 days. Of 15.76, 22.72 and 25.92 mg N assimilated by the rice plants, 48, 61 and 62% was supplied by Azolla, Anabaena and Nostoc, respectively. The rest was obtained from the soil used.In the absence of the rice plants 30, 43 and 45% of applied¹⁵N of Azolla, Anabaena and Nostoc was released, respectively, in 60 days of which 93–96% was lost as N₂ through denitrification.     

Screening for acetylcholinesterase inhibitory activity in cyanobacteria of the genus Nostoc

Fifty-four cyanobacterial strains of the genus Nostoc from different habitats were screened for acetylcholinesterase inhibitory activity. Water-methanolic extracts from freeze-dried biomasses were tested for inhibitory activity using Ellman's spectrophotometric method. Acetylcholinesterase inhibitory activity higher than 90% was found in the crude extracts of Nostoc sp. str. Lukesova 27/97 and Nostoc ellipsosporum Rabenh. str. Lukesova 51/91. Extracts from Nostoc ellipsosporum str. Lukesova 52/91 and Nostoc linckia f. muscorum (Ag.) Elenk. str. Gromov, 1988, CALU-980 inhibited AChE activity by 84.9% and 65.3% respectively. Moderate AChE inhibitory activity (29.1-37.5%) was found in extracts of Nostoc linckia Roth. str. Gromov, 1962/10, CALU-129, Nostoc muscorum Ag. str. Lukesova 127/97, Nostoc sp. str. Lhotsky, CALU-327 and Nostoc sp. str. Gromov, CALU-998. Extracts from another seven strains showed weak anti-AChE activities. The active component responsible for acetylcholinesterase inhibition was identified in a crude extract of Nostoc sp. str. Lukesova 27/97 using HPLC and found to occur in one single peak.     

Microbiota of the Orchid rhizoplane

Six bacterial strains isolated from the underground roots of the terrestrial orchid Calanthe vestita var. rubrooculata were found to belong to the genera Arthrobacter, Bacillus, Mycobacterium, and Pseudomonas. Strains isolated from the aerial roots of the epiphytic orchid Dendrobium moschatum were classified into the genera Bacillus, Curtobacterium, Flavobacterium, Nocardia, Pseudomonas, Rhodococcus, and Xanthomonas. The rhizoplane of the terrestrial orchid was also populated by cyanobacteria of the genera Nostoc and Oscillatoria, whereas that of the epiphytic orchid was populated by one genus, Nostoc. In orchids occupying different econiches the spectra of the bacterial genera revealed differed. The microbial complex of the terrestrial orchid rhizoplane differed from that of the surrounding soil.     

Phenotypic and Genotypic Comparison of Symbiotic and Free-Living Cyanobacteria from a Single Field Site

PCR amplification techniques were used to compare cyanobacterial symbionts from a cyanobacterium-bryophyte symbiosis and free-living cyanobacteria from the same field site. Thirty-one symbiotic cyanobacteria were isolated from the hornwort Phaeoceros sp. at several closely spaced locations, and 40 free-living cyanobacteria were isolated from the immediate vicinity of the same plants. One of the symbiotic isolates was a species of Calothrix, a genus not previously known to form bryophyte symbioses, and the remainder were Nostoc spp. Of the free-living strains, two were Calothrix spp., three were Chlorogloeopsis spp. and the rest were Nostoc spp. All of the symbiotic and all but one of the free-living strains were able to reconstitute the symbiosis with axenic cultures of both Phaeoceros and the liverwort Blasia sp. Axenic cyanobacterial strains were compared by DNA amplification using PCR with either short arbitrary primers or primers specific for the regions flanking the 16S-23S rRNA internal transcribed spacer. With one exception, the two techniques produced complementary results and confirmed for the first time that a diversity of symbiotic cyanobacteria infect Phaeoceros in the field. Symbionts from adjacent colonies were different as often as they were the same, showing that the same thallus could be infected with many different cyanobacterial strains. Strains found to be identical by the techniques employed here were often found as symbionts in different thalli at the same locale but were never found free-living. Only one of the free-living strains, and none of the symbiotic strains, was found at more than one sample site, implying a highly localized distribution of strains.     

Cyanobiont specificity in some Nostoc-containing lichens and in a Peltigera aphthosa photosymbiodeme

The cyanobacterial symbionts in some Nostoc -containing lichens were investigated using the nucleotide sequence of the highly variable cyanobacterial tRNA^Leu (UAA) intron. When comparing different Nostoc -containing lichens, identical intron sequences were found in different samples of the same lichen species collected from two remote areas. This was true for all species where this comparison was made ( Peltigera aphthosa (L.) Willd., P. canina (L.) Willd. and Nephroma arcticum (L.) Torss.). With one exception, a specific intron sequence was never found in more than one lichen species. However, for two of the species, Peltigera aphthosa and Nephroma arcticum , two different cyanobionts were found in different samples. By examining a P. aphthosa photosymbiodeme it could be shown that the same Nostoc is present in both bipartite and tripartite lobes of this lichen. It is thus possible for one cyanobiont/ Nostoc to form the physiologically different symbioses that are found in bipartite and tripartite lichens. The connection between photobiont identity and secondary chemistry is discussed, as a correlation between differences in secondary chemistry and different cyanobionts/ Nostoc s in the species Peltigera neopolydactyla (Gyeln.) Gyeln. was observed. It is concluded that more knowledge concerning the photobiont will give us valuable information on many aspects of lichen biology.     

Distribution of Hydrogen-Metabolizing Bacteria in Alfalfa Field Soil

H₂ evolved by alfalfa root nodules during the process of N₂ fixation may be an important factor influencing the distribution of soil bacteria. To test this hypothesis under field conditions, over 700 bacterial isolates were obtained from fallow soil or from the 3-mm layer of soil surrounding alfalfa (Medicago sativa L.) root nodules, alfalfa roots, or bindweed (Convolvulus arvensis L.) roots. Bacteria were isolated under either aerobic or microaerophilic conditions and were tested for their capacity to metabolize H₂. Isolates showing net H₂ uptake and ³H₂ incorporation activity under laboratory conditions were assigned a Hup⁺ phenotype, whereas organisms with significant H₂ output capacity were designated as a Hout⁺ phenotype. Under aerobic isolation conditions two Hup⁺ isolates were obtained, whereas under microaerophilic conditions five Hup⁺ and two Hout⁺ isolates were found. The nine isolates differed on the basis of 24 standard bacteriological characteristics or fatty acid composition. Five of the nine organisms were isolated from soil around root nodules, whereas the other four were found distributed among the other three soil environments. On the basis of the microaerophilic isolations, 4.8% of the total procaryotic isolates from soil around root nodules were capable of oxidizing H₂, and 1.2% could produce H₂. Two of the Hup⁺ isolates were identified as Rhizobium meliloti by root nodulation tests, but the fact that none of the isolates reduced C₂H₂ under the assay conditions suggested that the H₂ metabolism traits were associated with various hydrogenase systems rather than with nitrogenase activity. Results from this study support the concept that H₂ evolution by alfalfa root nodules has a significant effect on the surrounding microenvironment and influences the number and diversity of bacteria occupying that region.     

Effect of Two Plant Species, Flax (Linum usitatissinum L.) and Tomato (Lycopersicon esculentum Mill.), on the Diversity of Soilborne Populations of Fluorescent Pseudomonads

Suppression of soilborne disease by fluorescent pseudomonads may be inconsistent. Inefficient root colonization by the introduced bacteria is often responsible for this inconsistency. To better understand the bacterial traits involved in root colonization, the effect of two plant species, flax (Linum usitatissinum L.) and tomato (Lycopersicon esculentum Mill.), on the diversity of soilborne populations was assessed. Fluorescent pseudomonads were isolated from an uncultivated soil and from rhizosphere, rhizoplane, and root tissue of flax and tomato cultivated in the same soil. Species and biovars were identified by classical biochemical and physiological tests. The ability of bacterial isolates to assimilate 147 different organic compounds and to show three different enzyme activities was assessed to determine their intraspecific phenotypic diversity. Numerical analysis of these characteristics allowed the clustering of isolates showing a high level (87.8%) of similarity. On the whole, the populations isolated from soil were different from those isolated from plants with respect to their phenotypic characteristics. The difference in bacteria isolated from uncultivated soil and from root tissue of flax was particularly marked. The intensity of plant selection was more strongly expressed with flax than with tomato plants. The selection was, at least partly, plant specific. The use of 10 different substrates allowed us to discriminate between flax and tomato isolates. Pseudomonas fluorescens biovars II, III, and V and Pseudomonas putida biovar A and intermediate type were well distributed among the isolates from soil, rhizosphere, and rhizoplane. Most isolates from root tissue of flax and tomato belonged to P. putida bv. A and to P. fluorescens bv. II, respectively. Phenotypic characterization of bacterial isolates was well correlated with genotypic characterization based on repetitive extragenic palindromic PCR fingerprinting.     

喀麦隆芋艿根腐病病原菌鉴定

从采自喀麦隆不同地区的芋艿(Xanthosoma mafaffa L.)病根及田土中分离菌株,分别从雅温得(Yaound(?))和巴马约(Mbalmayo)分离到的腐霉菌株XPMY和XPMM1,根据其形态学及生理学特征鉴定为群结腐霉Pythium myriotylum,用上述腐霉菌株的游动孢子悬液或菌丝体片断悬液人工接种,表现叶黄化及根腐等典型症状。用经常伴随群结腐霉的立枯丝核菌Rhizoctonia solani及茄镰孢Fusarium solani人工接种后均未表现症状。研究结果表明:群结腐霉Pythium myriotylum Drechsler是喀麦隆芋艿根腐病的致病菌。     

The structure and interrelationship of fungal populations in native and cultivated soils

Mitochondrial DNA haplotypes have been characterized for 120 isolates of the asexual fungus Fusarium oxysporum. Sixty of these isolates were obtained from soil in a native grassland in the San Joaquin Valley of California, including 20 isolates from each of six different sampling locations. The same sampling strategy was used to obtain 60 additional isolates from an agricultural field of the same soil type directly adjacent to the native soil. Twenty-three different mitochondrial DNA haplotypes were identified among the 120 isolates, including 11 haplotypes represented by two or more isolates and 12 that were unique. The five most common mitochondrial DNA haplotypes accounted for 93 (78%) of the 120 isolates. Isolates representing each of these five mitochondrial DNA haplotypes were found both in the cultivated and in the native soil. Seventy-two per cent of the isolates found in the cultivated soil were associated with the same mitochondrial DNA haplotype as one or more isolates in the native soil. The remaining isolates in the cultivated soil were associated with comparatively rare mitochondrial DNA haplotypes, most of which showed a close relationship to one of the haplotypes found in the native soil. Hierarchial gene diversity analysis indicated that a significant proportion of the mitochondrial DNA haplotype diversity was attributable to differences between sampling sites in the native soil but not in the cultivated soil. This may reflect significant spatial structuring of genetic diversity in populations of F. oxysporum in a native soil. The proportion of mtDNA haplotype diversity attributable to differences between populations in the native and cultivated soils was not significant. This suggests that our entire collection, encompassing strains from both native and cultivated soils, is representative of a single population of F. oxysporum.     

Biological Control of Fusarium oxysporum f.sp. asparagi by Applying Non-pathogenic Isolates of F . oxysporum

Root rot severity of asparagus plants grown in sterilized field soil inoculated with Fusarium oxysporum f . sp . asparagi (Foa) was reduced by more than 50% when the soil was precolo nized by each of 13 non - pathogenic (np) isolates of F. oxysporum originating from asparagus roots or field soils . In a greenhouse experiment , application of six np isolates to naturally infested field soil was followed by a 23 - 49% decrease of disease severity , depending on the isolate . One of them , Fo47 originating from Fusarium suppressive soil in France , was applied to field plots infested with Foa . Foa root rot was not suppressed in asparagus plants grown for 1 year in these plots . Pathogenic and np isolates extensively colonized the root surface and isolates of both types infected the roots of asparagus plants grown in sterilized field soil , with significant differences among the np isolates . Inoculation of sterilized field soil with np isolates reduced germination of Foa chlamydospores by 43 - 64% depending on the isolate used . It is concluded that np isolates of F. oxysporum can suppress asparagus root rot caused by Foa in naturally infested field soil . The differences for root colonization capacity among the np isolates imply that selection for this trait might reveal isolates that perform better under field conditions .     

Competition among symbiotic cyanobacterial Nostoc strains forming artificial associations with rice (Oryza sativa)

Competition among four symbiotically competent Nostoc strains, colonizing rice roots, was examined using hetR-DGGE (denaturing gradient gel electrophoresis) as strain identification. Although mixed in various combinations, only one strain at a time associated with the rice roots. Nostoc strain 8964:3 was the most competitive and our data suggest that its competitive fitness was dependent on rapid hormogonial spreading as displayed on agar plates. Furthermore, rice roots induced hormogonia in all tested Nostoc strains, but only Nostoc strain 9104 showed positive chemotaxis towards the root. Inhibition of growth of competing cyanobacterial strains was not apparent.     

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.     

Screening,production, optimization and characterization of cyanobacterial polysaccharide

Biotechnological applications of algal polysaccharide as emulsifiers, thickeners and laxatives have led to the screening and selection of certain diazotrophic filamentous cyanobacteria from saline/alkaline soil of Madhya Pradesh, India. Strain specific variation in cell bound, extracellular and total polysaccharide content was quantified under laboratory conditions. Among the cyanobacterial isolates examined Nostoc calcicola RDU-3 was found to produce highest amount (105 mg l⁻¹) of extracellular polysaccharide on 44th day of growth under diazotrophic growth conditions. Extracellular polysaccharide production of cyanobacterium Nostoc calcicola RDU-3 was optimal at pH-10, temperature 35°C, photoperiod of 24 h and in white light. The Gas Chromatographic analysis of polysaccharide from Nostoc calcicola RDU-3 revealed the presence of ribose (36.03%), xylose (34.13%), rhamnose (29.67%) and glucose (4.0%). The polysaccharide is novel in that it possesses ribose as the predominant monosaccharide with very low levels of glucose. Predominance of ribose monosaccharide is the unique feature which is reported to be used as metabolic supplement to the heart. IR spectrum of extracellular polysaccharide revealed the presence of sulphate group. Such sulphated polysaccharide is reported to have antiviral properties.