Aerobic nitrogen fixation is confined to a subset of cells in the non-heterocystous cyanobacterium Symploca PCC 8002

Symploca PCC 8002 Kützing is a filamentous cyanobacterium that lacks the specialized cells, known as heterocysts, that protect nitrogenase from O₂ in most aerobic N₂-fixing cyanobacteria. Nevertheless, Symploca is able to carry out N₂ fixation in the light under aerobic conditions. When cultures were grown under light/dark cycles, nitrogenase activity commenced and increased in the light phase and declined towards zero in the dark. Immunolocalization of dinitrogenase reductase in sectioned Symploca trichomes showed that the enzyme was present only in 9% of the cells. These cells lacked any obvious mechanical protection against atmospheric O₂ and their ultrastructural characteristics were similar to those of cells that did not contain any dinitrogenase reductase. The nitrogenase-containing cells possessed carboxysomes that were rich in ribulose-1,5-bisphosphate carboxylase/oxygenase and phycoerythrin, a light harvesting pigment of PS II. This indicates that these cells had a capacity for both N₂ fixation and photosynthesis. The significance of the localization pattern for dinitrogenase reductase is discussed in the context of N₂ fixation in Symploca PCC 8002.     

发光二极管光质对念珠藻葛仙米生长及生理生化特性的影响简

利用发光二极管(LED)作为光源,以冷百荧光灯光作为对照,研究不同光质[红光637 nm、绿光529 nm、蓝光453 nm、白光(400—700)nm]对念珠藻葛仙米生长和生理生化特性的影响。结果表明:在培养前期,红光促进藻蓝蛋白合成,而藻红蛋白合成受抑制;蓝光和绿光则促进藻蓝蛋白合成。在培养后期,红光处理有利于叶绿素a和类胡萝卜素积累,其含量分别达到干重的1.33%和0.24%;绿光、白光和冷白荧光培养物的相应色素的含量均约占1.0%和0.16%;蓝光培养物的相应色素含量分别仅为0.45%和0.11%。红光培养物的氨基酸含量达干重的23.1%,是对照的1.58倍。除蓝光外其他光质对还原糖的含量影响无显著差异。在培养过程中LED白光和冷白荧光培养物的平均相对生长速率分别约为其他色光培养物的1.3和1.5倍。     

Structural characterization of sulfated arabinans extracted from Cladophora glomerata Kützing and their macrophage activation

Water-soluble sulfated heteropolysaccharides were extracted from Cladophora glomerata Kützing and fractionated by ion-exchange chromatography, which yielded two subfractions, F₁ and F₂. The crude and fractionated polysaccharides (F₁ and F₂) mostly consisted of carbohydrates (62.8–74.5%) with various amounts of proteins (9.00–17.3%) and sulfates (16.5–23.5%), including different levels of arabinose (41.7–54.4%), galactose (13.5–39.0%), glucose (0.80–10.6%), xylose (6.84–13.4%), and rhamnose (0.20–2.83%). Based on the size exclusion chromatography (SEC) profiles, the crude and fractions mainly contained one peak with shoulders having molecular weight (M_w) ranges of 358–1,501 × 10³. The F₁ fraction stimulated RAW264.7 cells to produce considerable amounts of nitric oxide and cytokines compared to the crude and F₂ fraction. The backbone of the most potent immunostimulating fraction (F₁) was α-(1→4)-L-arabinopyranoside with galactose and xylose residues as branches at O-2 position, and sulfates mainly at O-2 position as well.     

Photoregulated or Energy Dependent Process of Hormogonia Differentiation in Nostoc sphaeroides Kutzing （Cyanobacterium）

Abstract: Hormogonium, which was thought to play an important role in the dispersal and survival of these microorganisms in their natural habitats, is a distinguishable developmental stage of heterocystous cyanobacteria. The present study examined the effects of different light conditions and sugars on the differentiation of Nostoc sphaeroides Kützing to the hormogonia stage. Results showed that differentiation of hormogonia was light dependent in the absence of sugar, but that close to 100% of cyanobacteria differentiated to hormogonia in the presence of glucose or sucrose, irrespective of the light conditions. This differentiation was inhibited, even in the presence of sugars, upon application of an inhibitor of respiration. Following the testing of different sugars, the effects of different lights were examined. It was found that 5–10 umol‐nT2‐s‐1 photon flux density was optimal for hormogonia differentiation. One hundred percent differentiation was obtained with white light irradiation, in contrast with irradiation with green light (80% differentiation) and red light (0–10% differentiation). Although they showed different efficiencies in inducing hormogonia differentiation in N. sphaeroides, the green and red radiation did not display antagonistic effects. When the additional aspect of time dependence was investigated through the application of different light radiations and an inhibitor of protein synthesis, it was found that the initial 6 h of the differentiation process was crucial for hormogonia differentiation. Taken together, these results show that hormogonia differentiation in N. sphaeroides is either a photoregulated or an energy dependent process. (Managing editor: Ping HE)     

Edible blue-green algae reduce the production of pro-inflammatory cytokines by inhibiting NF-κB pathway in macrophages and splenocytes

Background

Chronic inflammation contributes to the development of pathological disorders including insulin resistance and atherosclerosis. Identification of anti-inflammatory natural products can prevent the inflammatory diseases.

Methods

Anti-inflammatory effects of blue-green algae (BGA), i.e., Nostoc commune var. sphaeroides Kützing (NO) and Spirulina platensis (SP), were compared in RAW 264.7 and mouse bone marrow-derived macrophages (BMM) as well as splenocytes from apolipoprotein E knockout (apoE^−/−) mice fed BGA.

Results

When macrophages pretreated with 100 μg/ml NO lipid extract (NOE) or SP lipid extract (SPE) were activated by lipopolysaccharide (LPS), expression and secretion of pro-inflammatory cytokines, such as tumor necrosis factor α (TNFα), interleukin 1β (IL-1β), and IL-6, were significantly repressed. NOE and SPE also significantly repressed the expression of TNFα and IL-1β in BMM. LPS-induced secretion of IL-6 was lower in splenocytes from apoE^−/− fed an atherogenic diet containing 5% NO or SP for 12 weeks. In RAW 264.7 macrophages, NOE and SPE markedly decreased nuclear translocation of NF-κB. The degree of repression of pro-inflammatory gene expression by algal extracts was much stronger than that of SN50, an inhibitor of NF-κB nuclear translocation. Trichostatin A, a pan histone deacetylase inhibitor, increased basal expression of IL-1β and attenuated the repression of the gene expression by SPE. SPE significantly down-regulated mRNA abundance of 11 HDAC isoforms, consequently increasing acetylated histone 3 levels.

Conclusion

NOE and SPE repress pro-inflammatory cytokine expression and secretion in macrophages and splenocytes via inhibition of NF-κB pathway. Histone acetylation state is likely involved in the inhibition.

General significance

This study underscores natural products can exert anti-inflammatory effects by epigenetic modifications such as histone acetylation.