Effect of UV-B radiation on the synthesis of UV-absorbing compounds in a terrestrial cyanobacterium, Nostoc flagelliforme

Effects of two intensities (1 and 5 W?m^?2) of UV-B radiation on the synthesis of UV-absorbing compounds in a terrestrial cyanobacterium Nostoc flagelliforme were investigated. UV-B radiation resulted in lower biomass. Short period (less than 12 h) of UV-B radiation caused an increase of chlorophyll a content, but subsequent duration of treatment (more than 24 h) resulted in a rapid decrease. N. flagelliforme synthesized UV-absorbing compounds such as scytonemin and mycosporine-like amino acids (MAAs) in response to UV-B radiation. Upon 48 h of exposure to UV-B radiation, scytonemin content in cells increased by 103.8 and 164.0 % at 1 and 5 W?m^?2, respectively. Oligosaccharide-linked mycosporine-like amino acids increased by 145.5 % after 12 h at 5 W?m^?2 and 114.5 % after 48 h at 1 W?m^?2 UV-B radiation. HPLC analysis showed that nine MAAs existed in N. flagelliforme cells both from liquid suspension culture and field colony. But the concentration and kinds of them were different. At the two distinct levels of UV-B radiation, the content of particular MAAs increased, declined, or remained unchanged. Moreover, the appearance of two new MAAs was observed.     

The odd behaviour of carbonic anhydrase in the terrestrial cyanobacterium Nostoc flagelliforme during hydration-dehydration cycles

The terrestrial cyanobacterium Nostoc flagelliforme , inhabiting arid areas, withstands prolonged periods of dehydration. How dehydration and occasional wetting affect inorganic C acquisition in this organism is not well known. As inorganic C acquisition in cyanobacteria often involves carbonic anhydrases (CA), we studied the effect of cycles of hydration and dehydration on the extracellular and intracellular CA activities, at the pH values presumably associated with dew or rain wetting. The external CA of N. flagelliforme (or of the microorganismal consortium of which N. flagelliforme is the main component) is activated by hydration, especially at low pH, and it may facilitate inorganic C acquisition when N. flagelliforme colonies are wetted by dew. Internal CA is present in dry colonies and is rapidly inactivated upon rehydration, therefore an anaplerotic role for this enzyme is proposed.     

Growth characteristics of the cyanobacterium Nostoc flagelliforme in photoautotrophic, mixotrophic and heterotrophic cultivation

Nostoc flagelliforme is a terrestrial cyanobacterium with high economic value. Dissociated cells separated from a natural colony of N. flagelliforme were cultivated for 7 days under either phototrophic, mixotrophic or heterotrophic culture conditions. The highest biomass, 1.67 g L⁻¹ cell concentration, was obtained under mixotrophic culture, representing 4.98 and 2.28 times the biomass obtained in phototrophic and heterotrophic cultures, respectively. The biomass in mixotrophic culture was not the sum as that in photoautotrophic and heterotrophic cultures. During the first 4 days of culture, the cell concentration in mixotrophic culture was lower than the sum of those in photoautotrophic and heterotrophic cultures. However, from the 5th day, the cell concentration in mixotrophic culture surpassed the sum of those obtained from the other two trophic modes. Although the inhibitor of photosynthetic electron transport DCMU [3-(3,4-dichlorophenyl)-1,1-dimethylurea] efficiently inhibited autotrophic growth of N. flagelliforme cells, under mixotrophic culture they could grow by using glucose. The addition of glucose changed the response of N.flagelliforme cells to light. The maximal photosynthetic rate, dark respiration rate and light compensation point in mixotrophic culture were higher than those in photoautotrophic cultures. These results suggest that photoautotrophic (photosynthesis) and heterotrophic (oxidative metabolism of glucose) growth interact in mixotrophic growth of N. flagelliforme cells.     

Effect of mixed carbon substrate on exopolysaccharide production of cyanobacterium Nostoc flagelliforme in mixotrophic cultures

The effects of organic carbon sources on cell growth and exopolysaccharide (EPS) production of dissociated Nostoc flagelliforme cells under mixotrophic batch culture were investigated. After 7?days of cultivation, glycerol, acetate, sucrose, and glucose increased the final cell density and final EPS concentrations, and mixotrophic growth achieved higher biomass concentrations. The increase in cell growth was particularly high when glucose was added as the sole carbon source. On the other hand, EPS production per dry cell weight was significantly enhanced by adding acetate. For more effective EPS production, the effects of the mixture of glucose and acetate were investigated. Increasing the ratio of glucose to acetate resulted in higher growth rate with BG-11 medium and higher EPS productivity with BG-11₀ medium (without NaNO₃). When the medium was supplemented with a mixture of glucose (4.0?g?L^?1) and acetate (2.0?g?L^?1), 1.79?g?L^?1 biomass with BG-11 medium and 879.6?mg?L^?1 of EPS production with BG-11₀ medium were achieved. Adopting this optimal ratio of glucose to acetate established in flask culture, the culture was also conducted in a 20-L photobioreactor with BG-11 medium for 7?days. A maximum biomass of 2.32?g?L^?1 was achieved, and the EPS production was 634.6?mg?L^?1.     

干旱胁迫对发菜超微结构及抗性生理的影响

发菜是一种陆生固氮蓝藻,具有强烈的旱生生态适应性。对干旱胁迫条件下发菜超微结构和抗性生理进行了研究。结果表明：随着干旱胁迫加重,发菜细胞大小和细胞壁厚度变化不显著,胶质鞘趋于紧密,类囊体排列趋于紊乱,多角体变得模糊不清甚至消失,糖原颗粒数目减少,但结构颗粒数目没有明显变化。随着干旱胁迫的加重,发菜SOD、CAT活性呈先升高再下降趋势,SOD在含水量为120%时达到高峰;CAT活性在含水量为445%时达到高峰;MDA,氧自由基随着干旱胁迫加重,其含量呈上升趋势;H₂O₂含量随干旱胁迫加重呈先升高再下降趋势,在含水量为120%时达到峰值。干燥储存1年的发菜与恢复活性的发菜有明显差异性,其SOD、CAT活性较低、MDA、H₂O₂含量较少,但是氧自由基含量最高。研究结果对深入研究发菜的耐旱机理奠定了基础。     

UV-B-induced synthesis of photoprotective pigments and extracellular polysaccharides in the terrestrial cyanobacterium Nostoc commune.

Liquid cultures of the terrestrial cyanobacterium Nostoc commune derived from field material were treated with artificial UV-B and UV-A irradiation. We studied the induction of various pigments which are though to provide protection against damaging UV-B irradiation. First, UV-B irradiation induced an increase in carotenoids, especially echinenone and myxoxanthophyll, but did not influence production of chlorophyll a. Second, an increase of an extracellular, water-soluble UV-A/B-absorbing mycosporine occurred, which was associated with extracellular glycan synthesis. Finally, synthesis of scytonemin, a lipid-soluble, extracellular pigment known to function as a UV-A sunscreen, was observed. After long-time exposure, the UV-B effect on carotenoid and scytonemin synthesis ceased whereas the mycosporine content remained constantly high. The UV-B sunscreen mycosporine is exclusively induced by UV-B (< 315 nm). The UV-A sunscreen scytonemin is induced only slightly by UV-B (< 315 nm), very strongly by near UV-A (350 to 400 nm), and not at all by far UV-A (320 to 350 nm). These results may indicate that the syntheses of these UV sunscreens are triggered by different UV photoreceptors.     

Effect of cell water amount on photosynthetic yield in the cyanobacterium Nostoc flagelliforme and involvement of NADPH dehydrogenase-mediated cyclic electron transport

Nostoc flagelliforme is a terrestrial cyanobacterium, and water is one of the most important factors limiting its photosynthetic yield. The aims of the present study were to investigate the effect of cell water amount on photosynhetic yield and the role of NADPH dehydrogenase (NDH-1)-mediated cyclic electron transport in this effect. The role of NDH-1-mediated cyclic electron transport was assessed by measuring NDH-1 expression, several chlorophyll fluorescence parameters, and photosynthetic O₂ evolution at several time points after cell water had been redried. The results indicated that the highest rate of NDH-1-mediated cyclic electron transport, reflected by post-illumination increase in chlorophyll fluorescence and NDH-1 amount, was only obtained when the cells contained about 1.8 times water relative to dry weight. This was consistent with observed changes in photosynthetic yield, reflected by O₂ evolution. However, the highest photochemical activity of photosystem II, reflected by F _v/F _m and qP, could be maintained when N. flagelliforme cells included water in a broad range. This implies that the effect of cell water amount on photosynthetic yield is related to NDH-1-mediated cyclic electron transport. The possible mechanisms of this effect are discussed.     

Crucial role of extracellular polysaccharides in desiccation and freezing tolerance in the terrestrial cyanobacterium Nostoc commune

The cyanobacterium Nostoc commune is adapted to the terrestrial environment and has a cosmopolitan distribution. In this study, the role of extracellular polysaccharides (EPS) in the desiccation tolerance of photosynthesis in N. commune was examined. Although photosynthetic O2 evolution was not detected in desiccated colonies, the ability of the cells to evolve O2 rapidly recovered after rehydration. The air-dried colonies contained approximately 10% (wt/wt) water, and field-isolated, natural colonies with EPS were highly water absorbent and were rapidly hydrated by atmospheric moisture. The cells embedded in EPS in Nostoc colonies were highly desiccation tolerant, and O2 evolution was not damaged by air drying. Although N. commune was determined to be a mesophilic cyanobacterium, the cells with EPS were heat tolerant in a desiccated state. EPS could be removed from cells by homogenizing colonies with a blender and filtering with coarse filter paper. This treatment to remove EPS did not damage Nostoc cells or their ability to evolve O2, but O2 evolution was significantly damaged by desiccation treatment of the EPS-depleted cells. Similar to the EPS-depleted cells, the laboratory culture strain KU002 had only small amount of EPS and was highly sensitive to desiccation. In the EPS-depleted cells, O2 evolution was also sensitive to freeze-thaw treatment. These results strongly suggest that EPS of N. commune is crucial for the stress tolerance of photosynthesis during desiccation and during freezing and thawing.     

Effects of solar UV radiation on morphology and photosynthesis of filamentous cyanobacterium Arthrospira platensis

To study the impact of solar UV radiation (UVR) (280 to 400 nm) on the filamentous cyanobacterium Arthrospira (Spirulina) platensis, we examined the morphological changes and photosynthetic performance using an indoor-grown strain (which had not been exposed to sunlight for decades) and an outdoor-grown strain (which had been grown under sunlight for decades) while they were cultured with three solar radiation treatments: PAB (photosynthetically active radiation [PAR] plus UVR; 280 to 700 nm), PA (PAR plus UV-A; 320 to 700 nm), and P (PAR only; 400 to 700 nm). Solar UVR broke the spiral filaments of A. platensis exposed to full solar radiation in short-term low-cell-density cultures. This breakage was observed after 2 h for the indoor strain but after 4 to 6 h for the outdoor strain. Filament breakage also occurred in the cultures exposed to PAR alone; however, the extent of breakage was less than that observed for filaments exposed to full solar radiation. The spiral filaments broke and compressed when high-cell-density cultures were exposed to full solar radiation during long-term experiments. When UV-B was screened off, the filaments initially broke, but they elongated and became loosely arranged later (i.e., there were fewer spirals per unit of filament length). When UVR was filtered out, the spiral structure hardly broke or became looser. Photosynthetic O(2) evolution in the presence of UVR was significantly suppressed in the indoor strain compared to the outdoor strain. UVR-induced inhibition increased with exposure time, and it was significantly lower in the outdoor strain. The concentration of UV-absorbing compounds was low in both strains, and there was no significant change in the amount regardless of the radiation treatment, suggesting that these compounds were not effectively used as protection against solar UVR. Self-shading, on the other hand, produced by compression of the spirals over adaptive time scales, seems to play an important role in protecting this species against deleterious UVR. Our findings suggest that the increase in UV-B irradiance due to ozone depletion not only might affect photosynthesis but also might alter the morphological development of filamentous cyanobacteria during acclimation or over adaptive time scales.     

Recovery of photosynthetic systems during rewetting is quite rapid in a terrestrial cyanobacterium, Nostoc commune

Recovery processes of photosynthetic systems during rewetting were studied in detail in a terrestrial, highly drought-tolerant cyanobacterium, Nostoc commune. With absorption of water, the weight of N. commune colony increased in three phases with half-increase times of about 1 min, 2 h and 9 h. Fluorescence intensities of phycobiliproteins and photosystem (PS) I complexes were recovered almost completely within 1 min, suggesting that their functional forms were restored very quickly. Energy transfer from allophycocyanin to the core-membrane linker peptide (L(CM)) was recovered within 1 min, but not that from L(CM) to PSII. PSI activity and cyclic electron flow around PSI recovered within 2 min, while the PSII activity recovered in two phases after a time lag of about 5 min, with half times of about 20 min and 2 h. Photosynthetic CO(2) fixation was restored almost in parallel with the first recovery phase of the PSII reaction center activity. Although the amount of absorbed water became more than 20 times the initial dry weight of the N. commune colony in the presence of sufficient water, about twice the initial dry weight was enough for recovery and maintenance of the PSII activity.     

Molecular genetic and chemotaxonomic characterization of the terrestrial cyanobacterium Nostoc commune and its neighboring species

The phylogeny of the terrestrial cyanobacterium Nostoc commune and its neighboring Nostoc species was studied using molecular genetic and chemotaxonomic approaches. At least eight genotypes of N. commune were characterized by the differences among 16S rRNA gene sequences and the petH gene encoding ferredoxin-NADP? oxidoreductase and by random amplified polymorphic DNA analysis. The genotypes of N. commune were distributed in Japan without regional specificity. The nrtP gene encoding NrtP-type nitrate/nitrite permease was widely distributed in the genus Nostoc, suggesting that the occurrence of the nrtP gene can be one of the characteristic features that separate cyanobacteria into two groups. The wspA gene encoding a 36-kDa water stress protein was only found in N. commune and Nostoc verrucosum, suggesting that these Nostoc species that form massive colonies with extracellular polysaccharides can be exclusively characterized by the occurrence of the wspA gene. Fifteen species of Nostoc and Anabaena were investigated by comparing their carotenoid composition. Three groups with distinct patterns of carotenoids were related to the phylogenic tree constructed on the basis of 16S rRNA sequences. Nostoc commune and Nostoc punctiforme were clustered in one monophyletic group and characterized by the occurrence of nostoxanthin, canthaxanthin, and myxol glycosides.     

Effects of amines and aminoalcohols on bovine intestine alkaline phosphatase activity

Bovine intestine alkaline phosphatase (BIALP) is widely used as a signaling enzyme in sensitive assays such as enzyme immunoassay (EIA). In this study, we evaluated the effects of various aminoalcohols and amines on the activity of BIALP in the hydrolysis of p-nitrophenyl phosphate (pNPP) at pH 9.8, at 20 °C. The k_cat values at 0.05 M diethanolamine, 0.1 M triethanolamine, and 0.2 M N-methylethanolamine were 190 ± 10, 840 ± 30, and 500 ± 10 s⁻¹, respectively. The k_cat values increased with increasing concentrations of diethanolamine, triethanolamine, and N-methylethanolamine and reached 1240 ± 60, 1450 ± 30, and 2250 ± 80 s⁻¹, respectively, at 1.0 M. On the other hand, the k_cat values at 0.05-1.0 M ethanolamine, ethylamine, methylamine, and dimethylamine were in the range of 100-600 s⁻¹. These results indicate that diethanolamine, triethanolamine and N-methylethanolamine highly activate BIALP and might be suitable as a dilution buffer of BIALP in EIA. Interestingly, the K_m values increased with increasing concentrations of diethanolamine and N-methylethanolamine, but not triethanolamine: the K_m value at 1.0 M diethanolamine (0.83 ± 0.15 mM) was 12-fold higher than that at 0.05 M (0.07 ± 0.01 mM), and that at 1.0 M N-methylethanolamine (2.53 ± 0.20 mM) was 14-fold higher than that at 0.2 M (0.18 ± 0.02 mM), while that at 1.0 M triethanolamine (0.31 ± 0.01 mM) was similar as that at 0.2 M (0.25 ± 0.01 mM), suggesting that the mechanisms of BIALP activation are different between the aminoalcohols.     

Effects of UV-B Radiation and Periodic Desiccation on the Morphogenesis of the Edible Terrestrial Cyanobacterium Nostoc flagelliforme

The terrestrial cyanobacterium Nostoc flagelliforme Berk. et M. A. Curtis has been a popular food and herbal ingredient for hundreds of years. To meet great market demand and protect the local ecosystem, for decades researchers have tried to cultivate N. flagelliforme but have failed to get macroscopic filamentous thalli. In this study, single trichomes with 50 to 200 vegetative cells were induced from free-living cells by low light and used to investigate the morphogenesis of N. flagelliforme under low UV-B radiation and periodic desiccation. Low-fluence-rate UV-B (0.1 W m(-2)) did not inhibit trichome growth; however, it significantly increased the synthesis of extracellular polysaccharides and mycosporine-like amino acids and promoted sheath formation outside the trichomes. Under low UV-B radiation, single trichomes developed into filamentous thalli more than 1 cm long after 28 days of cultivation, most of which grew separately in liquid BG11 medium. With periodic desiccation treatment, the single trichomes formed flat or banded thalli that grew up to 2 cm long after 3 months on solid BG11 medium. When trichomes were cultivated on solid BG11 medium with alternate treatments of low UV-B and periodic desiccation, dark and scraggly filamentous thalli that grew up to about 3 cm in length after 40 days were obtained. In addition, the cultivation of trichomes on nitrogen-deficient solid BG11 medium (BG11(0)) suggested that nitrogen availability could affect the color and lubricity of newly developed thalli. This study provides promising techniques for artificial cultivation of N. flagelliforme in the future.