PHOTOINDUCTION AND PHOTOREVERSAL OF THE NOSTOCACEAN DEVELOPMENTAL CYCLE(1)

Isolation and characterization of 1-palmitoyl-2-linoleoyl-sn-glycerol as a hormogonium-inducing factor (HIF) from the coralloid roots of Cycas revoluta (Cycadaceae)

Coralloid roots are specialized tissues of cycads (Cycas revoluta) that are involved in symbioses with nitrogen-fixing Nostoc cyanobacteria. We found that a crude methanolic extract of coralloid roots induced differentiation of the filamentous cell aggregates of Nostoc species into motile hormogonia. Hence, the hormogonium-inducing factor (HIF) was chased using bioassay-based isolation, and the active principle was characterized as a mixture of diacylglycerols (DAGs), mainly composed of 1-palmitoyl-2-linoleoyl-sn-glycerol (1), 1-palmitoyl-2-oleoyl-sn-glycerol (2), 1-stearoyl-2-linolenoyl-sn-glycerol (3), and 1-stearoyl-2-linoleoyl-sn-glycerol (4). Enantioselectively synthesised compound 1 showed a clear HIF activity at 1 nmol (0.6 µg) disc⁻¹ for the filamentous cells, whereas synthesised 2-linoleoyl-3-palmitoyl-sn-glycerol (1′) and 1-palmitoyl-2-linoleoyl-rac-glycerol (1/1′) were less active than 1. Conversely, synthesised 1-linoleoyl-2-palmitoyl-rac-glycerol (8/8′) which is an acyl positional isomer of compound 1 was inactive. In addition, neither 1-monoacylglycerols nor phospholipids structurally related to 1 showed HIF-like activities. As DAGs are protein kinase C (PKC) activators, 12-O-tetradecanoylphorbol-13-acetate (12), urushiol C15:3-Δ^10,13,16 (13), and a skin irritant anacardic acid C15:1-Δ⁸ (14) were also examined for HIF-like activities toward the Nostoc cells. Neither 12 nor 13 showed HIF-like activities, whereas 14 showed an HIF-like activity at 1 nmol/disc. These findings appear to indicate that some DAGs act as hormogonium-inducing signal molecules for filamentous Nostoc cyanobacteria.

Comparison of Nostocean hormogonium induction and its motility on solid plates between agar and gellan gum at varying gel matrix concentrations

To establish a sensitive bioassay for Nostocean hormogonium induction, we compared the effectiveness of the morpho-differentiation induction on two gelled plates, agar and gellan gum, for anacardic acid C15:1-Δ⁸ decyl ester (1) (100 nmol/disc). On BG-11₀ (nitrogen-free) medium-based 0.6 and 0.8% agar plates, Nostoc sp. strain Yaku-1 isolated from a coralloid root of Cycas revoluta in Yakushima Island showed clear morpho-differentiation from filamentous aggregates into hormogonia, and the induced hormogonia dispersed within 24 h; however, similar hormogonium formation was not observed at agar concentrations of 1.0% or higher. Conversely, hormogonium induction was considerably more pronounced on gellan gum plates than those on agar plates through concentrations ranging from 0.6 to 1.6% even after 12 h of incubation, particularly active on the 0.8-1.0% gellan gum plates. Thus, gellan gum plates can achieve clear results within 12 h and are thus highly useful for primary screening for hormogonium-inducing factors (HIFs).

Halotia gen. nov., a phylogenetically and physiologically coherent cyanobacterial genus isolated from marine coastal environments

Nostoc is a common and well-studied genus of cyanobacteria and, according to molecular phylogeny, is a polyphyletic group. Therefore, revisions of this genus are urged in an attempt to clarify its taxonomy. Novel strains isolated from underexplored environments and assigned morphologically to the genus Nostoc are not genetically related to the ‘true Nostoc’ group. In this study, four strains isolated from biofilms collected in Antarctica and five strains originated from Brazilian mangroves were evaluated. Despite their morphological similarities to other morphotypes of Nostoc , these nine strains differed from other morphotypes in ecological, physiological and genetic aspects. Based on the phylogeny of the 16S rRNA gene, the Antarctic sequences were grouped together with the sequences of the Brazilian mangrove isolates and Nostoc sp. Mollenhauer 1 : 1-067 in a well-supported cluster (74 % bootstrap value, maximum-likelihood). This novel cluster was separated phylogenetically from the ‘true Nostoc’ clade and from the clades of the morphologically similar genera Mojavia and Desmonostoc. The 16S rRNA gene sequences generated in this study exhibited 96 % similarity to sequences from the nostocacean genera mentioned above. Physiologically, these nine strains showed the capacity to grow in a salinity range of 1–10 % NaCl, indicating their tolerance of saline conditions. These results provide support for the description of a new genus, named Halotia gen. nov., which is related morphologically to the genera Nostoc , Mojavia and Desmonostoc. Within this new genus, three novel species were recognized and described based on morphology and internal transcribed spacer secondary structures: Halotia branconii sp. nov., Halotia longispora sp. nov. and Halotia wernerae sp. nov., under the provisions of the International Code of Nomenclature for Algae, Fungi and Plants.

Photoreversible pigment: occurrence in a blue-green alga

A new photoreversible pigment has been isolated from the blue-green alga Tolypothrix tenuis. This pigment bears certain resemblances to phytochrome, except that absorption maxima for the two forms are in the green and red portions of the spectrum instead of the red and far-red. The pigment may control diverse differentiative processes in blue-green algae.

Effects of alkaline earth metal ions on the growth of Calothrix strain RC3, a natural isolate from Rock Creek, British Columbia

Calothrix is a filamentous cyanobacterium that has a single terminal heterocyst and a tapering morphology. It exists in two forms: mature filaments as described and motile hormogonia, which have a distinct morphology and serve as a dispersal mechanism for the organism. These cyanobacteria are common inhabitants of freshwater environments, where they are subjected to a variety of fluctuating conditions, including levels of dissolved metal ions. The present study represented an initial investigation of the effects of increasing metal ion concentrations on Calothrix as assessed ultrastructurally by transmission electron microscopy and through alterations observable by light microscopy and growth studies. Exposure of filaments to various levels of the alkaline earth cations Ca2+, Mg2+, Sr2+, and Ba2+ led to various changes in structure, indicating effects on the organism's physiology. These included perturbation of cell envelope layers, such that the formation of outer membrane vesicles was enhanced, alteration to the patterns and abundance of sheath material formed, alteration of thylakoid (photosynthetic) membrane structure, and inhibition of hormogonium formation and release. It was interesting to note that even cations that are not typically thought of as toxic (Ca2+ and Mg2+) could have profound effects on the cells to the extent of inhibiting growth at the maximum levels used in this study (5 mM), which are below these often found in natural environments. These results give an indication that the presence of metal ions in natural environments can have an important influence on the structural and growth characteristics of commonly found cyanobacteria to the extent of making them appear, on a macroscopic basis, as different organisms entirely. This puts a note of caution on future field observations and interpretations of the effects of pollutants on natural microbial communities.Key words: cyanobacteria, metals, ultrastructure.

Sporulation and the development of planktonic blue-green algae in two Salopian meres

Factors affecting akinete formation and the survival of planktonic bluegreen algal populations after the formation of 'water blooms’ were investigated in two eutrophic kataglacial lakes. It is considered that the induction of sporulation may be due to extreme conditions at the water surface during the summer to which the algal bloom is exposed, rather than to nutrient, especially orthophosphate, deficiency. It has not been shown conclusively that akinetes constitute an overwintering stage of the planktonic algal life cycle, or that akinetes germinate in the spring to produce the inoculum for subsequent vegetative growth. Comparisons of planktonic, sedimenting and benthic algal material indicate that germination shortly after maturation may provide the greater part of the overwintering planktonic vegetative populations. Population sizes and life cycles appear to be influenced by the physical factors which control the stability of the water column.

B-Phycoerythrin from Rhodella violacea: characterization of two isoproteins

Two isoproteins of the "native" B-phycoerythrin of the red alga, Rhodella violacea, were purified from crude extracts by preparative polyacrylamide gel electrophoresis and subsequently characterized. The slower moving pigment in gel electrophoresis was designated B-PE I, the faster as B-PE II. Both were found to occur in about equal amounts. B-PE I has a molecular weight of about 280000 and an IEP at 4.39, B-PE II a molecular weight of nearly 265000 and an IEP at 4.23. B-PE I and II are characterized by absorption maxima at 568 and 542 nm and a shoulder at 500 nm in the visible part of the absorption spectra. Their absorption coefficients at 542 nm differ with values of 5.54 and 5.63, respectively. The fluorescence emission spectra show a single maximum at 575 for B-PE I and at 578 nm for B-PE II. Both spectra have a shoulder at 630 nm. The fluorescence yield of B-PE II is lower by 25%. In calibrated SDS gel electrophoresis of the purified pigments B-PE I and II show two subunits of molecular weights of 18900 and 29200 and 18500 and 29900, respectively. Quantitative amino acid analyses indicated, that the isoproteins are very similar. B-PE II, however, has a significantly higher content of acidic amino acids and a lower percentage of basic residues, which is in keeping with its lower isoelectric point. Functional aspects of the occurrence of two isoproteins of B-phycoerythrin are discussed.

Physiology and cytological chemistry blue-green algae

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Polychlorinated biphenyls: toxicity to certain phytoplankters

The growth rates of two species of marine diatoms were reduced by polychlorinated biphenyls (PCB's), widespread pollutants of the marine environment, at concentrations as low as 10 to 25 parts per billion. In contrast, a marine green alga and two species of freshwater algae were not inhibited at these or higher concentrations. The sensitivity of these species to PCB's paralleled their sensitivity to DDT [1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane].

Marine phytoplankton vary in their response to chlorinated hydrocarbons

Photosynthesis and growth in cultures of four marine phytoplankton species, isolated from different oceanic environments, were affected by three chlorinated hydrocarbons (DDT, dieldrin, and endrin) to varying extents. This ranged from complete insensitivity in Dunaliella to toxicity at concentrations of 0.1 to 1.0 part per billion of the pesticides in Cyclotella. Other forms were intermediate in their response.

DDT reduces photosynthesis by marine phytoplankton

Concentrations of DDT [1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane] as low as a few parts per billion in water reduced photosynthesis in laboratory cultures of four species of coastal and oceanic phytoplankton representing four major classes of algae, and in a natural phytoplankton community from Woods Hole, Massachusetts. Toxicity to diatoms increased as cell concentration decreased. This inhibition may be of ecological importance.