Bioactive natural products from blue-green algae

Since 1981 we have cultured and prepared lipophilic and hydrophilic extracts from more than 1500 strains representing some 400 species of blue-green algae. Screening for a wide variety of potentially useful bioactivities, including cytotoxic, multi-drug-resistance reversal, antifungal, and antiviral effects, has led to the discovery and identification of numerous novel bioactive metabolites including peptides, macrolides and glycosides.A systematic evaluation of the chemical and environmental factors that influence the production of secondary metabolites inScytonema ocellatum, which produces tolytoxin (a macrocyclic lactone that depolymerizes actinin vivo to disrupt cell division in eukaryotic organisms), has shown that cyanophytes can be manipulated in culture to improve growth and product yields.     

Mesosomes in blue-green algae

Summary Mesosome-like, unit-membrane structures are clearly defined in the blue-green algae, Spirulina and three strains of Synechococcus, after osmium or potassium permanganate fixation and observation with the electron microscope. The membranous structures are distinct from the photosynthetic membranes and, in the case of Spirulina, are frequently observed in cells and can occur in large volume within the cell.     

Studies with deoxyribonucleic acid from blue-green algae

Summary The total DNA in species of blue-green algae is similar to that of bacteria on an individual cell, but not on a dry weight, basis. The % G+C content of DNA from four species of blue-green algae has been determined by melting temperature measurement. An attempt tomeasure genetic homology between blue-green algae and certain bacterial species is described.     

Studies with deoxyribonucleic Acid from blue-green algae

DNA from two blue-green algae was isolated and characterized. The buoyant densities, thermal denaturation and renaturation, thermal melting values, base compositions, sedimentation coefficients, and molecular weights were determined. Blue-green algal DNA renatured extensively and at a comparable rate to that of bacterial DNA. The similarities among the kinds of DNA from bacteria and blue-green algae were interpreted to reflect a close relationship.     

Morphology-habitat associations in blue-green algae

Morphological and habitat features have been recorded on punchcards for three genera in the Oscillatoriaceae and two in the Nostocaceae. As a result it is concluded that generic divisions in the Oscillatoriaceae are arbitrary and artificial, but that in the Nostocaceae, Cylindrospermum represents a grouping of distinct forms to a greater degree than does the amorphous genus Anabaena.

Some morphological comparisons between the two groups are attempted and detectable associations between morphological and habitat features are suggested : together these may contribute to an eventual separation of taxa on a more logical basis than at present.     

Ammonia assimilation in blue-green algae

Summary The occurrence of alanine dehydrogenase (AlaDH), glutamate dehydrogenase (GDH), and 2-ketoglutarate: glutamine amidotransferase (GGAT), has been surveyed in a number of blue-green algae. Among nine unicellular strains grown with nitrate, and belonging to five of the major typological groups, AlaDH was present in seven, and GDH in all eight that were assayed. In ten filamentous strains grown with nitrate, and belonging to the three nonheterocyst-forming and four heterocyst-forming groups, AlaDH was present in six, but both AlaDH and GDH were present in only one strain. In those strains which could be grown with N₂ as sole nitrogen source, levels of GDH were generally lower, and AlaDH higher in cells fixing N₂ than in those growing with nitrate. GGAT was undetectable in N₂-grown cells. Two unicellular and three filamentous strains were tested for their ability to use L-alanine, L-glutamate, L-glutamine, and L-asparagine as sole sources of nitrogen. Of these, L-asparagine was utilized most effectively. There was little difference in levels of GDH in cells grown with nitrate or with L-asparagine, while the levels of AlaDH were slightly lower in cells grown with L-asparagine.     

Nitrogen chlorosis in blue-green algae

Summary Nitrogen deficient Anacystis nidulans contained normal levels of chlorophyll-a and carotenoids but did not contain any phycocyanin. These organisms also contained large amounts of polysaccharide. The addition of nitrate to a deficient culture resulted in the recovery of normal pigmentation over a period of several hours.The relation between these changes and growth was established by a kinetic study of the changes in cell composition during pigment loss and recovery. Loss of phycocyanin commenced with the cessation of growth due to nitrogen limitation and was complete after 15 hours. In contrast there were only minor changes in chlorophyll-a and carotenoid. After growth had ceased polysaccharide continued to increase and viability dropped sharply although total cell counts did not change. These trends were reversed by the addition of nitrate to deficient cultures. Phycocyanin was detected after a short lag and normal levels of phycobiliprotein were present within 8 hours. Cell division did not begin until normal levels of phycocyanin had been restored. During the recovery of normal pigmentation there was a decrease in reducing sugar content and a sharp rise in viability. Qualitative studies with 9 additional blue-green algae suggest that loss of phycocyanin is a characteristic feature of nitrogen deficiency in blue-green algae.     

Hydrocarbons in green and blue-green algae

Liquid column chromatography and thin-layer chromatography were used to determine the total content of hydrocarbons and gas chromatography was used to evaluate composition of hydrocarbons in green algae (Chlorella kessleri, C. vulgaris, Chlorella sp.,Scenedesmus acutus, S. acuminatus, S. obliquus) and the blue-green alga (Spirulina platensis) cultivated under autotrophic or heterotrophic conditions. InC. kessleri cultivated under heterotrophic conditions the content of hydrocarbons was found to be about 10^-2 % (per dry mass), whereas under autotrophic conditions it was about 10^-3 % (per dry mass). The highest content of hydrocarbons was detected in species of the genusScenedesmus cultivated autotrophically (10^-1 %). Heptadecane and hexacosane were found as major alkanes, 1-heptadecene was detected among alkenes.     

Heterocyst division in two blue-green algae

Bacteriophage 16-6-12 of Rhizobium lupini has a long, non-contractile tail and a head which is hexagonal in outline. The tail is 140 nm in length, 11 nm in diameter, and carries a short terminal fiber. Analysis of the tail structure by optical diffraction indicates that it is of the helical “stacked disc” type. After phenol-extraction from purified particles, the DNA of phage 16-6-12 can circularize in vitro. No significant difference in contour length was observed between the linear (14.34±0.28 μm) and circular (14.44±0.24 μm) forms of molecules. After partial denaturation with alkali an AT-GC-map was constructed, which shows an asymmetric distribution of AT- and GC-rich regions. It is concluded that this phage DNA can circularize due to the presence of cohesive ends and that it is not circularly permuted.