Symbiotic Cyanobacteria Research Articles

Heterotrophic metabolism and regulation of uptake hydrogenase activity in symbiotic cyanobacteria

Heterotrophic metabolism and regulation of uptake hydrogenase activity in symbiotic cyanobacteria

Identification of a common cyanobacterial symbiont associated with Azolla spp. through molecular and morphological characterization of free-living and symbiotic cyanobacteria

Symbiotically associated cyanobacteria from Azolla mexicana and Azolla pinnata were isolated and cultured in a free-living state. Morphological analyses revealed differences between the free-living isolates and their symbiotic counterparts, as did restriction fragment length polymorphism (RFLP) analyses with both single-copy glnA and rbcS gene probes and a multicopy psbA gene probe. RFLP analyses with Anabaena sp. strain PCC 7120 nifD excision element probes, including an xisA gene probe, detected homologous sequences in DNA extracted from the free-living isolates. Sequences homologous to these probes were not detected in DNA from the symbiotically associated cyanobacteria. These analyses indicated that the isolates were not identical to the major cyanobacterial symbiont species residing in leaf cavities of Azolla spp. Nevertheless, striking similarities between several free-living isolates were observed. In every instance, the isolate from A. pinnata displayed banding patterns virtually identical to those of free-living cultures previously isolated from Azolla caroliniana and Azolla filiculoides. These results suggest the ubiquitous presence of a culturable minor cyanobacterial symbiont in at least three species of Azolla.

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.

Limited Multiplication of Symbiotic Cyanobacteria of Azolla spp. on Artificial Media

We examined various media and conditions to isolate symbiotic cyanobacteria from the leaf cavities of Azolla spp. Cyanobacteria survived and multiplied to a limited extent on a medium with fructose, Casamino Acids, yeast extract, and NaNO(3) under 1% O(2). These cyanobacteria were antigenically identical to the endosymbionts.

Foliose Dictyoceratida of the Australian Great Barrier Reef III. Preliminary Electrophoretic Systematics

Abstract. Techniques of starch‐gel electrophoresis were applied in a taxonomic assessment of a difficult group of dictyoceratid sponges. A phylogenetic tree derived from the resultant electrophoretic characters agreed well with a recent taxonomic revision of this group produced in a companion study. However, this must be seen as a preliminary result, as the electrophoretic character set was restricted to only three enzyme systems due to the extensive effects of a nonspecific enzyme which precluded the effective interpretation of most other enzymes assayed. This non‐specific enzyme may be linked to a highly developed relationship between this group of sponges and symbiotic cyanobacteria.

The Hydrogenase-Nitrogenase Relationship in a Symbiotic Cyanobacterium Isolated From Macrozamia communis L. Johnson

The relationship between nitrogenase and hydrogenase activity in the cyanobacterial isolate from the corolloid roots of the cycad Macrozamia communis, grown both photoautotrophically and heterotrophically, has been investigated. The organism actively consumes hydrogen gas in both light and darkness in an oxygen-dependent reaction. The hydrogen consumption was substantially stimulated by light and was nickel-dependent. Nitrogenase activity was found not to be enhanced by hydrogen, either in the dark or light.

CARBON NUTRITION AND THE REGULATION OF UPTAKE HYDROGENASE ACTIVITY IN FREE-LIVING AND SYMBIOTIC ANABAENA CYCADEAE.

Anabaena cycadeae was grown with N2 as nitrogen source, either photoautotrophically in light or with glucose as carbon source in darkness. The rate of growth was much slower in darkness but the heterocyst frequency was much the same; nitrogenase activity (on a chlorophyll basis) was about half that of light-grown cells. Light-grown organisms contained uptake hydrogenase activity but dark-grown organisms did not. The addition of glucose to light-grown organisms was followed by the disappearance of uptake hydrogenase activity over the following 48 hours and the disappearance was independent of light. Heterocyst frequency and nitrogenase activity were much less affected by glucose addition. A. cycadeae growing symbiotically in cycad roots had much higher heterocyst frequency and nitrogenase activity than the free-living form but no detectable uptake hydrogenase activity. It is suggested that the rate of supply of carbohydrate to the heterocyst controls the development of uptake hydrogenase activity and that the absence of this activity in the symbiotic cyanobacteria indicates that the organisms in the cycad roots have an ample supply of carbohydrate.

Evidence for an ammonium transport system in free-living and symbiotic cyanobacteria

The free-living cyanobacterium Anabaena variabilis showed a biphasic pattern of 14CH3NH 3 + uptake. Initial accumulation (up to 60 s) was independent of CH3NH 3 + metabolism, but long-term uptake was dependent on its metabolism via glutamine synthetase (GS). The CH3NH 3 + was converted into methylglutamine which was not further metabolised. The addition of l-methionine-dl-sulphoximine (MSX), to inhibit GS, inhibited CH3NH 3 + metabolism, but did not affect the CH3NH 3 + transport system.

Net Primary Productivity in Coral Reef Sponges

Nine of the ten most common sponge species on the fore-reef slope of Davies Reef(Great Barrier Reef) contain symbiotic cyanobacteria. Six of the ten are net primary producers, with three times more oxygen produced by photosynthesis than is consumed during respiration. Light interception is enhanced by morphological flattening, thereby increasing the potential for phototrophic nutrition, a factor crucial in the ecology of most sessile coral reef invertebrates.

Abundance and production rates of floating diatom mats (Rhizosolenia castracanei and R. imbricata var. shrubsolei) in the Eastern Pacific Ocean

Abundance and production rates were measured on freefloating mats composed of the diatoms Rhizosolenia castracanei and R. imbricata var. shrubsolei in the California Current and boundary waters of the central North Pacific during October, 1980. Mats ranged from 3.0 to 10.6 cm in maximum length and had a mean volume of 6.4 ml. Production rates of the diatom mats averaged 4.0 μg C colony-1 h-1, more than 103 times higher than that of an equal volume of surrounding water. However, because of their low density at these sites, about 1 mat m-3, diatom mats contributed only about 1% of the total primary production. The two large Rhizosolenia species comprised almost all of the phytoplankton biomass within the mats. Rhizosolenia species rarely occurred in seawater between mats, where the phytoplankton community was dominated by a diverse array of nannoplankton. The Rhizosolenia species in the mats appeared to be in healthy condition and contained intracellular bacteria. The very high production rates of the colonies indicate high nutrient demand and, since these particular diatoms lack the symbiotic cyanobacterium Richelia intracellularis, which is implicated in N-fixation in other species of Rhizosolenia, our results indicate that other nutrient sources must be present. We discuss the potential role of the intracellular bacteria in nitrogen fixation.

Glutamate Synthase Activity in Symbiotic Cyanobacteria

Glutamate synthase (GOGAT) activities of the symbiotic cyanobacteria of the lichens Peltigera canina and Peltigera aphthosa and of the water fern Azolla caroliniana have been determined and, like glutamine synthetase (GS) activity, found to be substantially reduced compared with the activities found in the free-living cyanobacteria. A similar reduction in GOGAT activity was not noted in the symbiotic green alga (Coccomyxa sp.) in P. aphthosa. The selective reduction of GS-GOGAT activity in symbiosis may be related to the production of extracellular nitrogen by the symbiotic cyanobacterium.

The ultrastructure of Anabaena azollae in Azolla pinnata

The water fern Azolla pinnata R. Br. was collected in Northwestern India and its structure was examined using scanning and transmission electron microscopy. Emphasis was given to the symbiotic cyanobacterium. Anabaena azollae, and to its relationship to the hairs of the leaf cavities. The cyanobacterial filaments are loosely arranged and often adhere to the protruding hairs and the folded cell walls of the cavities. The vegetative cells show a typical bilayered cell wall. Thylakoids are few and evenly dispersed in mature vegetative cells and appear to lack phycobilisomes. Clusters of polyglucoside granules are distinguished between the thylakoids. Thylakoid membranes are often seen forming whirls and lattices. Polyhedral bodies (carboxysomes) appear particularly frequently in younger cells and in the proximity of polyphosphate bodies. Presence of structured granules, often positioned at both sides of the cross‐wall of neighbouring vegetative cells, suggest a positive nitrogen balance. A high frequency of heterocysts is noted, while spores are not observed.The outer cell wall of the unbranched, mostly two‐celled, hairs shows frequent invaginations. The cytoplasma of the mature hair contains numerous organelles, and is penetrated by an electron transparent network with blebs and vesieles appearing. The exchange of metabolites between the symbiotic partners is discussed in relation to the structures noted.

The occurrence of fimbriae on a N 2 2 -fixing cyanobacterium which occurs in lichen symbiosis

The Nostoc cyanobiont of the lichen Peltigera canina when grown on N2 possesses, in the motile stage, discrete unbranched non-flagellar appendages (fimbriae or pili). These arise from the host cell surface in a peritrichous manner, have an axial hole, are 7.0 ±0.3 nm in diameter and are up to 3 μm long. They do not haemagglutinate guinea pig red blood corpuscles and differ from the major fimbrial types reported for Gram-negative heterotrophic bacteria and from sex pili. They may be involved in motility and specificity in symbiotic cyanobacteria.

Nitrogen fixation in coral reef sponges with symbiotic cyanobacteria

NITROGEN FIXATION by endosymbiotic cyanobacteria (blue-green algae) results in an important input of nitrogen into terrestrial ecosystems1; however, there is as yet little information on its significance in the marine environment2,3. Symbiosis of cyanobacteria with marine animals, although rare, is known to occur in an echiuroid worm4 and in sponges from coral reefs5 and the Mediterranean6. In the present study of sponge–cyanobacterial symbioses, several sponges from a coral reef in the Red Sea were tested, using the acetylene reduction technique7, immediately after their collection on reef-based platforms for their ability to fix nitrogen. Nitrogenase activity was detected in two sponges with cyanobacteria but not in a third with no cyanobacteria. This is the first demonstration of nitrogenase activity in an animal with symbiotic cyanobacteria. In two previous reports of nitrogen fixation in marine animals, the activity was attributed to bacteria in the gut8,9. Although these preliminary experiments are not sufficient to assess the significance of cyanobacterial nitrogenase activity in sponges, it is possible that any additional fixed nitrogen would be beneficial to sponges in tropical waters which are low in available nitrogen10 and in particulate nutrients11,12.

Transplantation of marine sponges to different conditions of light and current

Transplantation was employed to determine how marine sponges grow in different in situ conditions of light and current. The growth of Verongia aerophoba (Schmidt), which contained symbiotic cyanobacteria. was enhanced in light, particularly when sediment was excluded by a clear shield. V. cavernicola Vacelet and Chondrosia reniformis Nardo. which did not contain cyanobacteria, grew preferentially in the shade and were inhibited by light. The growth of Petrosia ficiformis (Poirct) and Chondrilla nucula Schmidt, which may or may not contain cyanobacteria. did not appear to be favoured by either light or shade. The growth of sponges in lower current speeds was considerably reduced ; this reduction was. however, partially reversed in those sponges with cyanobacteria when grown in the light. Presumably symbiotic cyanobacteria are beneficial to sponges growing in the light because they transfer photosynthetically fixed nutrient and shield the underlying tissue. Significant morphological differences were observed in sponges grown under different environmental conditions.

Microbial associations in sponges. III. Ultrastructure of the in situ associations in coral reef sponges

Symbiotic cyanobacteria are associated with marine sponges in three ways: the majority are free-living in the mesohyl; large aggregates occur in “cyanocytes” (specialized, vacuolated archeocytes); and few are present in digestive vacuoles. The cyanobacteria in Jaspis stellifera and Neofibularia irata are morphologically similar to those described in Mediterranean sponges, whereas those in Pericharax heteroraphis are different. The freeliving bacterial populations are morphologically similar, although the number of bacteria varies between the species. The fourth sponge Ircinia wistarii contains a mixed bacterial population unlike those in the other sponges. Sponge digestion of microbial associates is rare and not considered to contribute significant nutrients.