The program of protein synthesis during heterocyst differentiation in nitrogen-fixing blue-green algae

The program of protein synthesis that accompanies cellular differentiation following transfer of the blue-green alga Nostoc muscorum from nitrogen-containing to nitrogen-free medium has been determined by polyacrylamide gel electrophoresis of whole cell proteins labeled with ³⁵SO₄⁼ during successive intervals of the differentiation. Differentiating cells (proheterocysts, which become heterocysts) are distinguished from vegetative cells on the basis of the latter's susceptibility to lysis with lysozyme.At least ten sets of proteins can be distinguished on the basis of the time at which they are synthesized or the type of cell in which they are located. Regulation of most of these sets can be accounted for by classical induction or repression involving NH₄⁺ or a simple derivative of NH₄⁺. An additional mechanism is required to explain how the synthesis of several sets of proteins is initiated in all cells following transfer to nitrogen-free medium, but is permitted to continue only in developing proheterocysts. The structural polypeptides of the nitrogenase enzyme complex are members of the latter set.In differentiated filaments, very few proteins are synthesized in both vegetative cells and heterocysts. The qualitatively different pattern of protein synthesis is established very early, within the first 9 hr after transfer. Moreover, the proteins present in proheterocysts at that time are already qualitatively different from those of vegetative cells. Rapid turnover of vegetative cell proteins appears to be a characteristic of the early development of proheterocysts.     

Physiological studies on nitrogen-fixing blue-green algae

Summary The various types of blue-green algae known to fix nitrogen are considered. Particular attention has been paid to the effects of oxygen and other physiological parameters on nitrogenase activity and on the ecological distribution of the group. Data on nitrogen fixation by cell-free extracts of blue-green algae are presented.     

Effects of some amino acid analogues on growth and heterocyst formation in the blue-green algaNostoc linckia

The effects of two amino acid analogues, viz., L-methionine-DL-sulphoximine and L-methyl-DL-methionine on growth, heterocyst differentiation and nitrogen fixation in the blue-green algaNostoc linckia have been studied with special reference to heterocyst spacing pattern. L-methionine-DL-sulphoximine strongly inhibited growth but produced an unusual number of heterocysts with changed heterocyst spacing pattern in both nitrogen-free and ammonium-containing media. L-methyl-DL-methionine was less effective than L-methionine-DL-sulphoximine. An attempt was also made to counteract the toxic effects of these analogues by supplying amino acids. Glutamine and methionine reversed the inhibitory effect of L-methionine-DL-sulphoximine while only methionine reversed the inhibitory effect of L-methyl-DL-methionine. Production of changed heterocyst spacing pattern in nitrogen-free and ammonium-containing media when supplemented with L-methionine-DL-sulphioximine suggests that ammonia may not be the inhibitor of heterocyst spacing pattern.     

The ultrastructure of the heterocyst and akinete of the blue-green algae

Summary The ultrastructure of the heterocyst and its development from the vegetative cell is described. The ultrastructure of the akinete is also described. The mature heterocyst (still attached to the filament) has an elaborate structure which is distinct from both that of the normal vegetative cell and the akinete (the normal reproductive cell).Despite the extra structural detail seen in the electron micrographs, the observations do not indicate a likely physiological role for the heterocyst. However, since the developing-mature heterocyst has an organised structure, it is probable that it has an active metabolism. In contrast, the detached heterocyst has a highly disorganised structure and, for this reason, it is likely to be metabolically inactive and incapable of germination.     

Evidence for nitrogenase-catalyzed hydrogen uptake in nitrogen-fixing filamentous blue-green algae

Abstract Two new strains of (heterocystous) Anabaena , one of them devoid of hydrogenase activity, were compared with respect to hydrogen-uptake activities. Evidence was obtained for a hydrogen-recycling pathway in the dark independent of hydrogenase, because a similar recycling activity is measured in both strains. This hydrogen uptake is dependent on substrates for nitrogenase (molecular nitrogen or acetylene) and can be abolished by oxygen treatment of filaments or by uncouplers. The findings are interpreted as nitrogenase itself being directly involved in the hydrogen-uptake mechanism.     

Nitrogenase activity,amino acid pool patterns and amination in blue-green algae

Summary The free amino acid pools in the nitrogen-fixing blue-green algae Anabaena cylindrica, A. flos-aquae and Westiellopsis prolifica contain a variety of amino acids with aspartic acid, glutamic acid and the amide glutamine being present in much higher concentrations than the others. This pattern is characteristic of that found in organisms having glutamine synthetage/glutamate synthetase [glutamine amide-2-oxoglutarate amino transferase (oxido-reductase)] as an important pathway of ammonia incorporation. Under nitrogen-starved conditions the level of acetylene reduction (nitrogen fixation) and the glutamine pool both increase but the free ammonia pool decreases, suggesting that ammonia rather than glutamine regulates nitrogen fixation.Glutamine synthetase has been demonstrated in Anabaena cylindrica using the -glutamyl transferase assay and also using a biosynthetic assay in which P_i release from ATP during glutamine synthesis was measured. The enzyme (-glutamyl transferase assay) is present in nitrogen-fixing cultures and activity is higher in aerobic than in microaerophilic cultures. Ammonium-grown cultures have lowest levels of all and activity in the presence of nitrate-nitrogen (150 mg nitrogen 1^-1) is lower than in aerobic cultures growing on elemental nitrogen. Ammonium-nitrogen and nitrate-nitrogen have no effect on glutamine synthetase in vitro. Glutamate synthetase also operates in nitrogen-fixing cultures of Anabaena cylindrica.     

Action of 2,4-dichlorophenoxyacetic acid and rifampicin on heterocyst differentiation in the blue-green alga,Nostoc linckia

2,4-Dichlorophenoxyacetic acid, a commonly used herbicide, increased the growth of the filamentous blue-green alga,Nostoc linckia at doses upto 100 μg /ml. The herbicidetreated N₂-cultures showed enhanced heterocyst frequency and N₂-growth. Thus, the herbicide stimulated algal growth at the expense of molecular nitrogen under aerobic growth conditions. Rifampicin caused chain formation of heterocysts. This was effectively counteracted by 2,4-dichlorophenoxyacetic acid, suggesting a biological interaction between them at the level of the heterocyst spacing control mechanism.     

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.     

太湖蓝藻滤液的遗传毒性研究

蓝藻爆发是环境污染引发的重要事件之一,随之产生的蓝藻毒素又直接危及区域水安全.该论文采用蚕豆和大蒜根尖微核试验研究了太湖蓝藻暴发期间蓝藻滤液的遗传毒性.结果表明,同阴性对照相比,所有试验处理对蚕豆根尖细胞微核发生率的影响显著增加;对大蒜根尖细胞微核发生率而言除蓝藻滤液8倍稀释液的影响不显著外,其它水平效应显著高于阴性对照,而且表现出一定的剂量效应.暴发期蓝藻滤液原液对蚕豆根尖细胞微核发生率影响显著高于阳性对照(0.8mg·mL^-1环磷酰胺)的效应,从而说明蓝藻暴发时期蓝藻滤液具有较强的遗传毒性.通过微核试验效果分析,蚕豆作为植物监测系统的敏感性和稳定性都优于大蒜材料.     

Antimicrobial effects of Cellvibrio on blue-green algae

Summary The culture fluids from two Cellvibrio strains, in the stationary phase of growth, are shown to contain heat-resistant, low molecular weight substances with antibiotic-like effects on blue-green algae. Morphological changes and lysis of cells were observed in various species of blue-green algae; ultrastructural changes were noted in the cell walls of growing vegetative cells of Anabaena inaequalis. The viability of resting cells, including heterocysts and akinetes was not affected.     

Effect of rifampicin (3-(4-methylpiperazinyl-iminomethyl)rifamycin) on heterocyst differentiation in the blue-green algae Anabaena and Calothrix.

Chains of multiple heterocysts form in Anabaena und Calothrix filaments on treatment with rifampicin. The multiple heterocysts form irrespective of whether the rifampicin treatment is given in combined nitrogen-free or supplemented medium. This suggests the possibility of involvement of a species of RNA or of protein as intracellular heterocyst inhibitor and indicates that some latent pattern-determining mechanism may operate in the combined nitrogen medium.     

The effect of light on growth and development of two nitrogen fixing blue-green algae

Summary Green, blue, yellow, red and white light all support spore germination whereas vegetative growth occurs only in red, yellow or white light. This indicates a requirement of nonphotosynthetic light for spore germination and of photosynthetic light for growth and cell divisions. The green or blue light is neither inhibitory to vegetative growth nor to sporulation of red, yellow or white light grown filaments. The growth promoting effect of white light is greater than that of red or yellow light. Whereas spore germination is not affected by the intensity of white light, vegetative growth increases linearly with increase in white light intensity.     

Isolation and characterization of rapidly-growing,marine, nitrogen-fixing strains of blue-green algae

Five strains of heterocystous blue-green algae capable of high rates of growth and nitrogenase activity were isolated from shallow coastal environments. Growth of the organisms was characterized with respect to temperature, NaCl concentration in the medium, and nitrogen source. The temperature optima ranged from 35–42°C, and all but one of the strains displayed a requirement for added NaCl. The generation times under N₂-fixing conditions were 5.1–5.9 h, and were as low as 3.4 h for growth on NH₄Cl. Nitrogenase activity (C₂H₂ reduction) was high throughout the logarithmic growth phase of each strain. The maximum value observed for one strain was 65.5 nmoles C₂H₄ produced/mg protein x min, and the average values for the five strains ranged from 24.5–46.7 nmoles C₂H₄/mg protein x min. The organisms all belong to the genusAnabaena. The growth and nitrogenase activity of these strains are much higher than those of the heterocystous blue-green algae commonly used for investigation of nitrogen metabolism, and they thus should prove to be useful physiological tools. Their prevalence, as judged by the ease of their enrichment and isolation, in bay and estuarine environments suggests that they are important contributors of combined nitrogen.