The effects of ultrasound on cyanobacteria

The use of ultrasound for the control of algae and in particular for Microcystis aeruginosa has been investigated. The results indicate that sonication may provide a more environmentally friendly and more effective method for the control of cyanobacteria blooms than conventional treatments.Algae blooms occur frequently and globally in water bodies and are a major concern in terms of their effects on other species such as plants, fish and other microorganisms together with the potential danger to human health from cyanobacterial toxins that are carcinogenic. In addition to removing the algae itself ultrasound can also degrade such toxins. A range of ultrasonic conditions (in terms of frequency and intensity) have been studied under laboratory conditions together with a small number of pilot (field) studies that confirm the potential for ultrasonic treatment of algae on a large scale.     

The effects of pyridoxine deficiency and of caloric restriction on lipids in the developing rat brain

Abstract— The effects of dietary deficiency of pyridoxine upon the contents of lipids in the brain were determined at several times after birth for three groups of rats. The mothers of the nursing pups were fed one of the following dietary regimes: pyridoxine-deficient diet ad lib., pyridoxine-supplemented diet ad lib., or pyridoxine-supplemented diet in restricted amounts. At 7 and 14 days of postnatal age there were no significant differences between supplemented and deficient animals for any of the cerebral lipids studied. At 21 days the content of sphingomyelin in the brains of deficient animals was significantly lower than that in brains from the supplemented or calorically restricted animals in terms of percentage of total lipid and phospholipid phosphorus or tissue weight. On a per brain basis the content of sphingomyelin in the brains of calorically-restricted rats was significantly lower than in the brains of rats fed the supplemented diet ad lib. The contents of cerebrosides but not of sulphatides or ceramides were also significantly lower in brains of the deficient group than in brains from the other two groups. The contents of pyridoxine in brains and in livers of the deficient animals were considerably lower than the contents found in the same organs of the other dietary groups. The results suggest that one reason for the abnormal development of the brains of rats on a pyridoxine-deficient diet during the early postnatal period may be due to decreased quantities of sphingolipids.     

Arginine and nitrogen mobilization in cyanobacteria

Cyanobacteria have evolved mechanisms to adapt to environmental stress and nutrient availability, including accumulation of storage compounds in inclusions and granules. As arginine is a key building block of cyanophycin, a dynamic nitrogen reservoir in many cyanobacteria, arginine metabolism plays a key role in cyanobacterial nitrogen storage and remobilization. Recently, an arginine dihydrolase AgrE/ArgZ was identified as a major arginine‐degrading enzyme in nondiazotrophic Synechocystis, which catalyzes the conversion of arginine into ornithine and ammonia. The N‐terminal domain of AgrE/ArgZ is responsible for arginine dihydrolase activity. Burnat et al. (2019) identified the arginine catabolic pathway in diazotrophic Anabaena, which starts with the reaction catalyzed by AgrE/ArgZ. Moreover, this study identified the C‐terminal domain of AgrE/ArgZ as an ornithine cyclodeaminase that catalyze the conversion of ornithine to proline. The results demonstrated that arginine is catabolized to generate glutamate by the concerted action of AgrE/ArgZ and bifunctional proline oxidase PutA in the vegetative cells of Anabaena. These findings expand our knowledge on nitrogen mobilization and redistribution in Anabaena under nitrogen‐fixation conditions. AgrE/ArgZ is widely present in many diazotrophic cyanobacteria and may be important for their contribution to marine nitrogen fixation. AgrE/ArgZ may have potential applications in metabolic engineering and biotechnology.     

Growth and nitrogen fixation by immobilized cyanobacteria

Summary The nitrogen-fixing photosynthetic cyanobacteria have significant potential for utilization as a biological system for the production of reduced nitrogen compounds, either by industrial fermentation or in the environment as soil inocula. In either system, the ability to immobilize cyanobacteria on the external surface of fibrous substrata would significantly improve the ease of manipulation of the cells, control of growth, and product recovery without the complications inherent in immobilization by entrapment. We have shown that the filamentous heterocystous species Nostoc muscorum is naturally able to attach to a variety of different fibres, both natural and artificial. Attached cells are able to grow and fix nitrogen in both liquid and plate culture. Nitrogen-fixing cells attach to the fibres much more readily than do non-fixing cells, suggesting that the physiological and morphological changes accompanying heterocyst differentiation result in the production of specific attachment sites. Scanning electron microscopy of attached cells shows that heterocysts act as attachment sites and that the external cell wall material specifically synthesized around the heterocysts may be acting as the biological glue for this attachment.Journal Paper No. J-13259 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa, Project No. 2649     

水华蓝藻对鱼类的营养毒理学效应

水体富营养化导致蓝藻水华的发生已成为全球关注的水环境问题,很多鱼类处于水生态系统食物链的最高级,蓝藻水华的主要次级代谢产物-微囊藻毒素可通过鱼类的摄食活动或生物富集作用在鱼体组织中累积,并通过食物链危及人类健康。近年来,微囊藻毒素对鱼类的毒性效应引起众多科学家的关注。在天然水体中不少鱼类可以主动摄食蓝藻,所以,水华蓝藻对鱼类来说既具有营养物作用、也具有潜在的毒性作用。鉴于目前机械收获的水华蓝藻生物量资源化利用问题以及水产饲料业亟需大力开发鱼粉替代蛋白源的需要,从营养学和毒理学这两个角度来研究水华蓝藻对鱼类的营养作用和毒性效应具有较高的理论和现实意义。主要概述了蓝藻粉、蓝藻细胞对鱼类的营养学和毒理学效应,以期拓展水华蓝藻对鱼类毒性效应的研究视野,同时也为水华蓝藻的资源化利用提供新的思路。     

Effects of nitrogen nutritional deficiency on the distribution of particular lipids in a eutrophic lake milieu]

The seasonal distribution of particulate lipids coupled with N-nutrient availability was studied in eutrophic Lake Aydat (Massif Central, France). The concentrations of lipids ranged between 196.9 and 2971.5 micrograms.l-1 (mean +/- s.d. = 1090.1 +/- 705.5 micrograms.l-1. Lipids were abundant in summer and fall when nitrates were insufficient reflecting thus an orientation of cell metabolism towards an accumulation of storage products. In such conditions, the heterocystous Cyanobacteria were found to develop due to their competitive advantage of exploiting atmospheric nitrogen. Their lipid metabolism did not seem to be affected at least partially by NO3- exhaustion.     

The development and effects of nitrogen deficiency in field-grown kiwifruit (Actinidia deliciosa) vines

The development and effects of nitrogen (N) deficiency in kiwifruit (Actinidia deliciosa Hayward) vines planted at three densities (25.0, 12.5 and 8.33 m² vine^–1) were examined in a long term (1982 to 1989) field experiment in which N was applied at rates from 0 to 200 kg N ha^–1 year^–1. The rate of applied N significantly affected leaf N concentrations every year from 1985 onwards, and the average leaf N concentrations declined throughout the experiment. Fruit N concentrations varied significantly with the level of applied N as early as 1986. The average fruit N concentrations varied strongly between years, and were inversely proportional to the fruit number (per m²), indicating that, after fruit set, growth of individual fruit was relatively insensitive to the vine N status. Effects of N supply on fruit yields resulted mostly from changes in fruit number (per m²). For vines planted at the high density, fruit yields responded significantly to the level of applied N each season from 1986 onwards. In any year, maximum fruit yields for vines planted at the high density were associated with leaf N concentrations (20 weeks after bud burst) of at least 1.8 mmol g^–1. For vines planted at low density, significant yield responses to the level of applied N were not recorded until 1988, and maximum yields in that year were associated with leaf N concentrations of at least 1.4 mmol g^–1. The delayed expression of effects of N deficiency on fruit yields for vines planted at low density appeared to follow a shift in partitioning of resources in favour of fruit growth. This shift in partitioning did not appear to be sustainable, and by 1989 the fruit yield response to applied N continued to the highest N level tested. In that year, the leaf N concentration associated with maximum yield was 1.8 mmol g^–1, the same as that recorded throughout the experiment for the vines planted at high density. In the last two seasons of the experiment, leaf necrosis developed extensively on vines receiving less than the highest rate of N. This necrosis appeared to be premature senescence resulting from N deficiency. Leaf chloride (Cl) concentrations increased significantly with increasing severity of N deficiency, but were never more than those associated with Cl toxicity. While N supply significantly affected fruit firmness immediately post-harvest, there were no significant effects on fruit firmness after 12–20 weeks storage.     

Structure and molecular organization of the photosynthetic accessory pigments of cyanobacteria and red algae

Summary Cyanobacteria (blue-green algae) and Rhodophyta (red algae) contain high concentrations of photosynthetic accessory pigments (phycobiliproteins) which trap light energy in the region between 400 and 650 nm. The electronic excitation energy is then transferred along a chain of these pigments to the reaction center chlorophyll of Photosystem II by a radiationless induced resonance process.Unlike the protein-chlorophyll complexes in the photosynthetic lamellae, the phycobiliproteins are readily soluble in aqueous solution, can be isolated in a variety of assembly forms, and crystallize readily. These properties facilitate the study of the structure of these proteins by chemical, physical, and immunological methods, as well as by X-ray diffraction and electron microscopy.The brilliantly colored phycobiliproteins are a homologous family of conjugated proteins of differing spectroscopic properties. The basic structural unit in these proteins is a monomer of 30,000–40,000 daltons made up of two dissimilar polypeptide chains, and . Each subunit carries covalently linked tetrapyrrole prosthetic groups related to the bile pigment biliverdin.The distinctive spectroscopic properties of each phycobiliprotein are a consequence of the chemical structure of the bile pigment it carries, and of the influence of the conformation and aggregation state of the protein on the spectra of these prosthetic groups. In vivo, the phycobiliproteins are organized into particles, phycobilisomes, attached in a regular array to the outer surface of the photosynthetic lamellae. Studies on phycobilisomes, and on intact cells, indicate the following pathway of energy transfer.Phycoerythrin Phycocyanin (_max 560 nm) (_max 620 nm) Allophycocyanin Allophycocyanin B (_max 650 nm)(_max 671 nm) Chlorophyll a (_max 680 nm)The amounts of the various phycobiliproteins in the cell are influenced by the intensity and energy distribution of the incident radiation. The phenomena of intensity adaptation and complementary chromatic adaptation yield insights into the structure of phycobilisomes and the molecular basis of the plasticity of the structure of this light-harvesting system.Invited article.     

香蕉苗期氮素亏缺与补偿对植株生长和根系形态的影响

为探究氮素亏缺及亏缺后补偿供氮对蕉苗生长及其根系形态特征的影响,该研究以主要栽培品种基因组类型(AAA型和ABB型)的香蕉品种为材料,通过石英砂基质培养结合氮素亏缺与补偿处理,分析其株高、叶长、叶宽、新增绿叶数、地上部和根系的鲜重和干物质质量、根长和根表面积及根体积等指标的变化。结果表明：(1)亏缺30 d,香蕉苗呈现明显的缺氮表型症状,株高、叶长、叶宽及新增绿叶数均显著降低,根系干物质积累增加,品种Ⅰ、Ⅱ根系干物质分别提高64.71%、87.50%,根冠比增加,总根表面积分别增加4.38%、11.85%,体积分别增加71.78%、66.55%。(2)亏缺68 d,干物质积累受到明显抑制,品种Ⅰ、Ⅱ全株干物质质量降低33.74%、42.04%,根系干物质质量与常规处理无显著差异,根系形态参数变化趋势与轻度亏缺一致。(3)亏缺后补偿供氮,缺氮症状消失,植株生长指标恢复正常水平;品种Ⅰ、Ⅱ根系干物质质量显著增加51.22%、52.38%,根冠比显著高于常规处理,根系趋向正常形态生长,并且总根体积分别增加61.80%、45.92%;轻度氮素亏缺后适时补偿供氮,缺氮蕉苗可恢复正常生长,根系干物...     

The production of biomass and phycobiliprotein pigments in filamentous cyanobacteria: the impact of light and carbon sources

Cyanobacteria are recognized as producers of bioactive substances and phycobiliproteins, whose medicinal and functional food properties have led to increased interest in recent years. In the present study, the biomass production and phycobiliprotein content in cyanobacterial strains belonging to Anabaena, Nostoc and Spirulina genera were investigated under the conditions of continuous illumination and mixotrophic nutrition. The results showed that biomass production was strongly stimulated by continuous light in Spirulina strains (4.5-fold), and by organic carbon sources in N₂-fixing strains (2.1–2.8-fold). The strategy of cells to accumulate primarily blue pigment phycocyanin and bluish green allophycocyanin was revealed under tested conditions. Furthermore, in the case of Spirulina S1 grown with glycerol, the culture medium became dense and changed its colour to pink, which may indicate the release of compounds including pigment(s) outside the cell, the phenomenon that seem to be rare among cyanobacteria. Moreover, under continuous light, in this strain the highest biomass level of 4.0 mg/mL was achieved, wherein phycocyanin and allophycocyanin content was increased 12- and 16-fold, respectively, which indicates the high potential of this strain for further investigation.     

The relation between nitrogen deficiency and leaf senescence

Because the "mobilization" of nitrogen resulting from nutritional nitrogen deficiency is also prominent during leaf senescence, the characteristics of these two syndromes were compared. Oat plants ( Avena sativa L. cv. Victory) were raised on a nutrient solution, complete except for nitrogen supply (i.e., with only the seed protein as nitrogen source), and the senescence of their leaves was compared with that of controls grown on a full nutrient solution. The N-deficient plants flowered after forming only 4 leaves and each set a single seed. The nitrogen lack affected the content of chlorophyll somewhat more than the content of the amino acids or protein nitrogen. However, spraying the plants with kinetin solution was able to retain 20–30% of the chlorophyll and protein. During senescence, the chlorophyll appears to be less stable in the N-deficient leaves than in the controls, while the protein is somewhat more stable than in the controls. Also, when the detached leaves from N-deficient plants senesced in white light or in darkness, kinetin delayed their senescence almost as effectively as that of control leaves. Most strikingly, the stomata of N-deficient leaves after detachment and floating on water were largely closed in light, just as in senescence, but could be partially induced to open by kinetin treatment. Since stomatal closure has earlier been shown to cause senescence, the characteristic syndrome of foliar nitrogen deficiency is concluded to be partly that of senescence.     

Oxygen relations of nitrogen fixation in cyanobacteria.

The enigmatic coexistence of O2-sensitive nitrogenase and O2-evolving photosynthesis in diazotrophic cyanobacteria has fascinated researchers for over two decades. Research efforts in the past 10 years have revealed a range of O2 sensitivity of nitrogenase in different strains of cyanobacteria and a variety of adaptations for the protection of nitrogenase from damage by both atmospheric and photosynthetic sources of O2. The most complex and apparently most efficient mechanisms for the protection of nitrogenase are incorporated in the heterocysts, the N2-fixing cells of cyanobacteria. Genetic studies indicate that the controls of heterocyst development and nitrogenase synthesis are closely interrelated and that the expression of N2 fixation (nif) genes is regulated by pO2.     

Physiological effects of nitrogen deficiency and recovery on the macroalga Gracilariopsis lemaneiformis (Rhodophyta)

Algal metabolites are the most promising feedstocks for bio‐energy production. Gracilariopsis lemaneiformis seems to be a good candidate red alga for polysaccharide production, especially relating to the agar production industry. Nitrogen deficiency is an efficient environmental pressure used to increase the accumulation of metabolites in algae. However, there are no studies on the physiological effects of G. lemaneiformis in response to nitrogen deficiency and its subsequent recovery. Here we integrated physiological data with molecular studies to explore the response strategy of G. lemaneiformis under nitrogen deficiency and recovery. Physiological measurements indicated that amino acids and protein biosynthesis were decreased, while endogenous NH₄⁺ and soluble polysaccharides levels were increased under nitrogen stress. The expression of key genes involved in these pathways further suggested that G. lemaneiformis responded to nitrogen stress through up‐regulation or down‐regulation of genes related to nitrogen metabolism, and increased levels of endogenous NH₄⁺ to complement the deficiency of exogenous nitrogen. Consistent with the highest accumulation of soluble polysaccharides, the gene encoding UDP‐glucose pyrophosphorylase, a molecular marker used to evaluate agar content, was dramatically up‐regulated more than 4‐fold compared to the relative expression of actin after 4 d of nitrogen recovery. The present data provide important information on the mechanisms of nutrient balance in macroalgae.     

The nitrogen physiology of the marine N2-fixing cyanobacteria Trichodesmium spp

Trichodesmium spp. have proved to be enigmatic organisms, and their ecology and physiology are unusual among diazotrophs. Recent research shows that they can simultaneously fix N2 and take up combined nitrogen. The co-occurrence of these two processes is thought to be incompatible, but they could be obligatory in Trichodesmium spp. if only a small fraction of cells within a colony or along a filament are capable of N2 fixation. Combined nitrogen is released from cells during periods of active growth and N2 fixation, and concomitantly taken up by Trichodesmium spp. or cells living in association with colonies. Although the nitrogenase of Trichodesmium spp. is affected by high concentrations of combined nitrogen, it might be relatively less sensitive to low concentrations of combined nitrogen typical of the oligotrophic ocean and culture conditions. Nitrogenase activity and synthesis exhibits an endogenous rhythm in Trichodesmium spp. cultures, which is affected by the addition of nitrogen.