Studies on Photosynthesis,Respiration and Morphology of Nostoc flagelliforme

Nostoc flagelliforme Born. et Flah. is one of the terrestrial cyanobacteria naturally distributed in arid and semi-arid areas in the Northern and the North-western parts of China. The cyanobacterium is an edible delicacy with special medical value. However, commercial N. flagelliforme has nov been collected from the field only. For cultivation of this valuable cyanobacterium, it is necessary to understand how it grows and how it adapts to the environment.The experimental material was collected in Siziwangqi of Nei Monggol. The effects of light intensity, temperature, pH, salinity, length of thallus and rewetting on photosynthesis and respiration of N. fiagelli[orme were measured using an oxygen electrode. The results were as follows: The photosynthetic light compensation point was around 40–90μmol photons·m-2·s-1, the light saturation point was 1200μmol photons·m-2·s-1, and no photoinhibition appeared when the light intensity was increased to 1800μmol photons· m-2·s-1. N. fiagelliforme exhibited its photosynthetic and respiratory activities in the temperature range of 5–45℃. The optimum temperature for its photosynthesis was 25℃ and that for respiration was 35--40℃. Between pH range of 4.5–9.5 N. flagelliforme had photosynthetic activity and respiratory activity at pH range of 4-10, with optimum pH for photosynthesis at 7.5 and for respiration at 7.5–8.0. N. flagelliforme exhibited maximum net photosynthesis in 0.15mol/L of NaC1 in BG-11 medium. When the salinity was increased to 0.9 mol/L the net photosynthesis dropped down to zero. Respiration decreased concordantly with the increasing salinity as well. Maxima photosynthesis and respiration was also detected when the thallus of N. flagelliforme reached a length of 0.5cm and aftewords the more the length the less the activities. The recovery time attaining to the maximum photosynthesis and respiration activities after rewetting was dependent on storage time in dryness. The cyanobacterial mats after being reserved for 3 months, attained its maximum photosynthesis by 0.5h after rewetting, and that being reserved for 18 months needed 3.5h after rewetting. For respiration, the mats reserved for 3 months and 18 months required 5 minutes and lh after rewetting, respectively to attain its maximum. Under scanning electron microscope, cells of N. flagelliforme were wrapped up within a gluey sheath, and usually attached closely to each other in pairs and the filaments were uni-trichome with branches in some cases. The surface of thallus tip was rougher than other parts which meant that the tip portion had greater surface area beneficial to water absorption and cell growth.     

The iron superoxide dismutase from the filamentous cyanobacterium Nostoc PCC 7120. Localization, overexpression, and biochemical characterization

The nitrogen-fixing filamentous cyanobacterium Nostoc PCC 7120 (formerly named Anabaena PCC 7120) possesses two genes for superoxide dismutase, a unique membrane-associated manganese superoxide dismutase (MnSOD) and a soluble iron superoxide dismutase (FeSOD). A phylogenetic analysis of FeSODs shows that cyanobacterial enzymes form a well separated cluster with filamentous species found in one subcluster and unicellular species in the other. Activity staining, inhibition patterns, and immunogold labeling show that FeSOD is localized in the cytosol of vegetative cells and heterocysts (nitrogenase containing specialized cells formed during nitrogen-limiting conditions). The recombinant Nostoc FeSOD is a homodimeric, acidic enzyme exhibiting the characteristic iron peak at 350 nm in its ferric state, an almost 100% occupancy of iron per subunit, a specific activity using the ferricytochrome assay of (2040 +/- 90) units mg(-1) at pH 7.8, and a dissociation constant Kd of the azide-FeSOD complex of 2.1 mM. Using stopped flow spectroscopy it was shown that the decay of superoxide in the presence of various FeSOD concentrations is first-order in enzyme concentration allowing the calculation of the catalytic rate constants, which increase with decreasing pH: 5.3 x 10(9) M(-1) s(-1) (pH 7) to 4.8 x 10(6) M(-1) s(-1) (pH 10). FeSOD and MnSOD complement each other to keep the superoxide level low in Nostoc PCC 7120, which is discussed with respect to the fact that Nostoc PCC 7120 exhibits oxygenic photosynthesis and oxygen-dependent respiration within a single prokaryotic cell and also has the ability to form differentiated cells under nitrogen-limiting conditions.     

Physiology of<Emphasis Type="Italic">Anabaena khannae</Emphasis> and<Emphasis Type="Italic">Chlorococcum humicola</Emphasis> under fluoride stress

Sodium fluoride showed pH-dependent physiological responses in the two test microalgae Anabaena khannae and Chlorococcum humicola. A. khannae showed severe membrane damage with fluoride at low pH with leakage of pigments and electrolytes. Annihilation of photosynthesis along with inhibition in 14C uptake was observed at pH 6 with 50 mg/L fluoride. While respiration was less affected in the cyanobacterium, C. humicola showed 30 % inhibition in respiratory activity. Resistance of C. humicola to fluoride toxicity has been attributed to the hindrance provided by the thick cell envelope, intracellular compartmentation and increase in extracellular pH as a consequence of its metabolism.     

Resistance of Spirulina platensis to Ammonia at High pH Values

Spirulina platensis is an alkalophilic cyanobacterium, exhibitingoptimal growth at pH 9.0 to 10.0. It grows well at pH 11.5 butnot at pH 7.0. Unlike many other photosynthetic microorganisms,it is capable of utilizing ammonia³ even at high pH values,and is resistant to the ammonia-mediated uncoupling of photosynthesis.The entry of ammonia into the cells is pH-dependent, and islimited by a relatively high average internal pH. This highpH value appears to be maintained predominantly by a high intrathylakoidpH. (Received November 20, 1990; Accepted July 3, 1991)     

Induction of anaerobic, photoautotrophic growth in the cyanobacterium Oscillatoria limnetica.

Anaerobic photoautotrophic growth of the cyanobacterium Oscillatoria limnetica was demonstrated under nitrogen in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (5micron), a constant concentration of Na2S (2.5 mM), and constant pH (7.3). The photoanaerobic growth rate (2 days doubling time) was similar to that obtained under oxygenic photoautotrophic growth conditions. The potential of oxygenic photosynthesis is constitutive in the cells; that of anoxygenic photosynthesis is rapidly (2 h) induced in the presence of Na2S in the light in a process requiring protein synthesis. The facultative anaerobic phototrophic growth physiology exhibited by O. limnetica would seem to represent an intermediate physiological pattern between the obligate anaerobic one of photosynthetic bacteria and the oxygenic one of eucaryotic algae.     

Evidence for HCO(3) Transport by the Blue-Green Alga (Cyanobacterium) Coccochloris peniocystis

The possibility of HCO₃⁻ transport in the blue-green alga (cyanobacterium) Coccochloris peniocystis has been investigated. Coccochloris photosynthesized most rapidly in the pH range 8 to 10, where most of the inorganic C exists as HCO₃⁻. If photosynthesis used only CO₂ from the external solution the rate of photosynthesis would be limited by the rate of HCO₃⁻ dehydration to CO₂. Observed rates of photosynthesis at alkaline pH were as much as 48-fold higher than could be supported by spontaneous dehydration of HCO₃⁻ in the external solution. Assays for extracellular carbonic anhydrase were negative. The evidence strongly suggests that HCO₃⁻ was a direct C source for photosynthesis.     

Role of dark respiration in photoinhibition of photosynthesis and its reactivation in the cyanobacterium Anacystis nidulans

Photoinhibition of photosynthesis and its reactivation was studied in the cyanobaterium A. nidulans in the presence of the respiratory inhibitor sodium azide, the uncouplers carbonyl cyanide p -(trifluoromethoxy)-phenylhydrazone (FCCP) and carbonyl cyanide m -chlorophenylhydrazone (CCCP) and the photosystem I elicitor phenazine methosulphate (PMS). Inhibition of dark respiration by azide increased the susceptibility of the cyanobacterium to photoinhibition. Both FCCP and CCCP also remarkably affected the process of photoinhibition in A. nidulans. The PMS at lower photoinhibitory light intensity partially protected A. nidulans from photoinhibition. The recovery from photoinhibition in the presence of azide or FCCP was slow and normal photosynthesis could not be resumed even after a longer period of incubation under suitable reactivating condition. Thus dark respiration has a key function in the process of photoinhibition of photosynthesis and its reactivation in the cyanobacterium A. nidulans.     

Na+ requirement for growth, photosynthesis, and pH regulation in the alkalotolerant cyanobacterium Synechococcus leopoliensis

We have found that Na+ is required for the alkalotolerance of the cyanobacterium Synechococcus leopoliensis. Cell division did not occur at any pH in the absence of Na+, but cells inoculated into Na+-free growth medium at pH 6.8 did continue metabolic activity, and over a period of 48 h, the cells became twice their normal size. Many of these cells remained viable for at least 59 h and formed colonies on Na+ -containing medium. Cells grown in the presence of Na+ and inoculated into Na+ -free growth medium at pH 9.6 rapidly lost viability. An Na+ concentration of ca. 0.5 milliequivalents X liter-1 was required for sustained growth above pH 9.0. The Na+ requirement could be only partially met by Li+ and not at all by K+ or Rb+. Cells incubated in darkness in growth medium at pH 6.8 had an intracellular pH near neutrality in the presence or absence of Na+. When the external pH was shifted to 9.6, only cells in the presence of Na+ were able to maintain an intracellular pH near 7.0. The membrane potential, however, remained high (-120 mV) in the absence or presence of Na+ unless collapsed by the addition of gramicidin. Thus, the inability to maintain a neutral intracellular pH at pH 9.6 in the absence of Na+ was not due to a generalized disruption of membrane integrity.Even cells containing Na+ still required added Na+ to restore photosynthetic rates to normal after the cells had been washed in Na+ -free buffer at pH 9.6. This requirement was only partially met by Li+ and was not met at all by K+, Rb+, Cs+ Mg2+, or Ca2+. The restoration of photosynthesis by added Na+ occurred within 30 s and suggests a role for extracellular Na+. Part of our results can be explained in terms of the operation of an Na+/H+ antiporter activity in the plasma membrane, but some results would seem to require other mechanisms for Na+ action.     

Microscale vertical profiles of n(2) fixation, photosynthesis, o(2), chlorophyll a, and light in a cyanobacterial assemblage

Profiles of N(2) fixation, O(2) production (gross photosynthesis), O(2) concentration, chlorophyll a concentration, and photon fluence rates were measured with 50-mum resolution in colonies of the heterocyst-forming cyanobacterium Nostoc parmelioides. Microelectrode measurements were made after 20 h of incubation under N(2) gas. Colonies were frozen, and 50-mum sections were prepared by using a freezing microtome and analyzed for N enrichment and chlorophyll a concentration. Colonies exhibited steep spatial gradients in rates of gross photosynthesis, O(2) concentration, and irradiance, with the highest values generally occurring at the surface. O(2) concentration, photosynthesis, and irradiance all showed positive correlations, but chlorophyll a concentrations varied independently of photosynthesis and irradiance. Forty-four percent of the variation in N incorporation was explained by gross photosynthesis (a positive correlation) when incorporation of N was expressed per unit of biomass (chlorophyll a).     

Sulfide and pH effects on variable fluorescence of photosystem II in two strains of the cyanobacterium Oscillatoria amphigranulata

Changes in fluorescence of photosystem II (PS II) chlorophyll were used to monitor the in vivo effects of sulfide and pH on photosynthesis by the cyanobacterium Oscillatoria amphigranulata. O. amphigranulata is capable of both oxygenic photosynthesis and sulfide dependent anoxygenic photosynthesis. A genetic variant of O. amphigranulata which photosynthesizes oxygenically at normal rates, but is incapable of anoxygenic photosynthesis and cannot tolerate sulfide, was also used to explore the mode of action of sulfide. In vivo fluorescence responses of PS II chlorophyll in the first few seconds of exposure to light (Kautsky transients) reflected the electrochemical states of PS II and associated electron donors and acceptors. Kautsky transients showed a distinct difference between PS II of the wild type and the variant, but sulfide lowered fluorescence in both. Kautsky transients with sulfide were similar to transients with addition of NH₂OH, NH₄ ⁺ or HCN, indicating sulfide interacts with a protein on the donor side of PS II. The fluorescence steady-state (after 2 min) was measured in the presence of sulfide, cyanide and ammonium with pH ranging from 7.2–8.7. Sulfide and cyanide had the most impact at pH 7.2, ammonium at pH 8.7. This suggests that the uncharged forms (HCN, NH₃ and H₂S) had the strongest effect on PS II, possibly because of increased membrane permeability.Abbreviations DCMU 3(3,4-dichlorophenyl)-1,1-dimethyl-urea - Oa-wt Oscillatoria amphigranulata (wild type) - Oa-2 Oscillatoria amphigranulata (genetic variant)     

Tolerance of the widespread cyanobacterium Nostoc commune to extreme temperature variations (?269 to 105°C), pH and salt stress

Nostoc commune is a widespread colonial cyanobacterium living on bare soils that alternate between frost and thaw, drought and inundation and very low and high temperatures. We collected N. commune from alternating wet and dry limestone pavements in Sweden and tested its photosynthesis and respiration at 20°C after exposure to variations in temperature (-269 to 105°C), pH (2-10) and NaCl (0.02-50 g NaCl kg(-1)). We found that dry field samples and rewetted specimens tolerated exposure beyond that experienced in natural environmental conditions: -269 to 70°C, pH 3-10 and 0-20 g NaCl kg(-1), with only a modest reduction of respiration, photosynthesis and active carbon uptake at 20°C. (14)CO(2) uptake from air declined markedly below zero and above 55°C, but remained positive. Specimens maintained a high metabolism with daily exposure to 6 h of rehydration and 18 h of desiccation at -18 and 20°C, but died at 40°C. The field temperature never exceeded the critical 40°C threshold during the wet periods, but it frequently exceeded this temperature during dry periods when N. commune is already dry and unaffected. We conclude that N. commune has an excellent tolerance to low temperatures, long-term desiccation and recurring cycles of desiccation and rewetting. These traits explain why it is the pioneer species in extremely harsh, nutrient-poor and alternating wet and dry environments.     

Effects of pH on the growth rate, motility and photosynthesis inEuglena gracilis

The influence of pH 3–10 on the growth, motility and photosynthesis inEuglena gracilis was demonstrated during a 7-d cultivation. The cells did not survive at pH<4 and >8, highest growth rate being detected at pH 7. Motility followed a similar patterns as growth rate. Photosynthetic response curves were shown to be of the same type over the whole pH range. High respiration was characteristic for cells grown at pH 5 and 6, the lowest one at 7. At high and also at low pH more active respiration was found which can be considered as a protective response on proton stress. Respiration was not completely inhibited with potassium cyanide. Photosynthesis was the most effective at pH 6; lower and higher pH decreased photosynthetic efficiency. pH affected more the growth rate than the photosynthesis.     

Biogeochemical processes in the algal-bacterial mats of the Urinskii alkaline hot spring

The structure and production characteristics of microbial communities from the Urinskii alkaline hot spring (Buryat Republic, Russia) have been investigated. A distinctive characteristic of this hot spring is the lack of sulfide in the issuing water. The water temperature near the spring vents ranged from 69 to 38.5°C and pH values ranged from 8.8 to 9.2. The total mineralization of water was less than 0.1 g/liter. Temperature has a profound effect on the species composition and biogeochemical processes occurring in the algal-bacterial mats of the Urinskii hot spring. The maximum diversity of the phototrophic community was observed at the temperatures 40 and 46°C. A total of 12 species of cyanobacteria, 4 species of diatoms, and one species of thermophilic anoxygenic phototrophic bacteria, Chloroflexus aurantiacus, have been isolated from mat samples. At temperatures above 40°C, the filamentous cyanobacterium Phormidium laminosum was predominant; its cell number and biomass concentration comprised 95.1 and 63.9%, respectively. At lower temperatures, the biomass concentrations of the cyanobacterium Oscillatoria limosa and diatoms increased (50.2 and 36.4%, respectively). The cyanobacterium Mastigocladus laminosus, which is normally found in neutral or slightly acidic hydrothermal systems, was detected in microbial communities. As the diatom concentration increases, so does the dry matter concentration in mats, while the content of organic matter decreases. The concentrations of proteins and carbohydrates reached their maximum levels at 45–50°C. The maximum average rate of oxygenic photosynthesis [2.1 g C/(m² day)], chlorophyll a content (343.4 mg/m²), and cell number of phototrophic microorganisms were observed at temperatures from 45 to 50°C. The peak mass of bacterial mats (56.75 g/m²) occurred at a temperature of 65–60°C. The maximum biomass concentration of phototrophs (414.63 × 10^?6 g/ml) and the peak rate of anoxygenic photosynthesis [0.42 g C/(m² day)] were observed at a temperature of 35–40°C.     

DO,pH, and Eh microprofiles in cyanobacterial granules from Lake Taihu under different environmental conditions

To understand characteristics of cyanobacterial granules from Lake Taihu, dissolved oxygen (DO), pH, and redox potential (Eh) microelectrodes were used to investigate physiological responses within these granules under different irradiance, temperature, and external pH levels. DO and pH levels increased with rising irradiance, while the Eh had an opposite trend. High light combined with high temperature decreased photosynthesis of the cyanobacterial granules. DO diffused from the surrounding water to the granules at low irradiance; however, DO began to diffuse from the granules to the water at high irradiance owing to increased photosynthesis. Dynamic changes of DO, pH, and Eh levels existed within the cyanobacterial granules under light–dark cycles. High DO levels within intercellular space of the cyanobacterial granules are another important buoyancy regulation mechanism. An external initial pH affected photosynthesis of the cyanobacteria in the granules. DO and pH levels of the granules in slightly alkaline solution (pH 8–9) were higher than those in highly alkaline solution (pH 10). Such physical and chemical characteristics within cyanobacterial granules in eutrophic water allowed them to outcompete other aquatic algae. The characterization of the physiological microenvironment within these cyanobacterial granules provides a new research approach to a better bloom management.     

Evidence for a sodium-dependent proline and glycine-betaine uptake in the cyanobacterium Nostoc muscorum

The cyanobacterium Nostoc muscorum is able to utilized proline and glycine-betaine as a nitrogen source under unstressed growth conditions. This cyanobacterium when grow in modified Chu No. 10 medium (without Na+) unable to utilized proline and glycine-betaine as a nitrogen source. Spontaneously occurring mutant clones defective in Na+ transport (Na+-R) were isolated and analyzed for proline and glycine-betaine utilization. The mutant phenotype showed normal heterocyst frequency and nitrogenase activity even in the medium containing 1 mM proline or 1 mM glycine-betaine, indicates the role of Na+ for proline/glycine-betaine uptake. The Na+-R mutant showed 100% survival at pH 11 and was simultaneously able to uptake and utilize proline/glycine-betaine at higher alkaline pH. This indicates that proline and glycine-betaine uptake systems are more efficient at higher alkaline pH. Since, the hypersaline environments are rich in Na+ contents and have alkaline pH, therefore it is suggested that the origin and evolution of specific compatible solutes may not depend only on the osmoregulatory role they play, but also on the other ecological factors operating simultaneously in the organism's niche.     

Microelectrode Studies of Interstitial Water Chemistry and Photosynthetic Activity in a Hot Spring Microbial Mat

Microelectrodes were used to measure oxygen, pH, and oxygenic photosynthetic activity in a hot spring microbial mat (Octopus Spring, Yellowstone National Park), where the cyanobacterium Synechococcus lividus and the filamentous bacterium Chloroflexus aurantiacus are the only known phototrophs. The data showed very high biological activities in the topmost layers of the microbial mat, resulting in extreme values for oxygen and pH. At a 1-mm depth at a 55°C site, oxygen and pH reached 900 μM and 9.4, respectively, just after solar noon, whereas anoxic conditions with a pH of 7.2 were measured before sunrise. Although diurnal changes between these extremes occurred over hours during a diurnal cycle, microbial activity was great enough to give the same response in 1 to 2 min after artificial shading. Oxygenic photosynthesis was confined to a 0.5- to 1.1-mm layer at sites with temperatures at or above about 50°C, with maximum activities in the 55 to 60°C region. The data suggest that S. lividus is the dominant primary producer of the mat.     

蓝藻化感抑制作用研究进展

在蓝藻水华的众多危害中,对其他生物的化感抑制效应是一个重要的方面,相关研究也越来越受到生态学及环境科学领域研究者的广泛关注.系统阐述了蓝藻化感抑制作用的现象、机理及条件,总结和归纳了具有化感抑制效应的蓝藻种类、化感物质及其作用对象,讨论了蓝藻化感抑制作用的生理生态机制、影响因素、研究方法及应用前景.在此基础上提出了该领域尚未解决的问题及今后的研究方向.     

Biogeochemical processes in the algal-bacterial mats of the Urinskii alkaline hot spring

The structure and production characteristics of microbial communities from the Urinskii alkaline hot spring (Buryat Republic, Russia) have been investigated. A distinctive characteristic of this hot spring is the lack of sulfide in the issuing water. The water temperature near the spring vents ranged from 69 to 38.5 degrees C and pH values ranged from 8.8 to 9.2. The total mineralization of water was less than 0.1 g/liter. Temperature has a profound effect on the species composition and biogeochemical processes occurring in the algal-bacterial mats of the Urinskii hot spring. The maximum diversity of the phototrophic community was observed at the temperatures 40 and 46 degrees C. A total of 12 species of cyanobacteria, 4 species of diatoms, and one species of thermophilic anoxygenic phototrophic bacteria, Chloroflexus aurantiacus, have been isolated from mat samples. At temperatures above 40 degrees C, the filamentous cyanobacterium Phormidium laminosum was predominant; its cell number and biomass concentration were 95.1 and 63.9%, respectively. At lower temperatures, the biomass concentrations of the cyanobacterium Oscillatoria limosa and diatoms increased (50.2 and 36.4%, respectively). The cyanobacterium Mastigocladus laminosus, which is normally found in neutral or slightly acidic hydrothermal systems, was detected in microbial communities. As the diatom concentration increases, so does the dry matter concentration in mats, while the content of organic matter decreases. The concentrations of proteins and carbohydrates reached their maximum levels at 45-50 degrees C. The maximum average rate of oxygenic photosynthesis (2.1 g C/m2 day), chlorophyll a content (343.4 mg/m2), and cell number of phototrophic microorganisms were observed at temperatures from 45 to 50 degrees C. The peak mass of bacterial mats (56.75 g/m2) occurred at a temperature of 65-60 degrees C. The maximum biomass concentration of phototrophs (414.63 x 10(-6) g/ml) and the peak rate of anoxygenic photosynthesis [0.42 g C/(m2 day)] were observed at a temperature of 35-40 degrees C.     

Evidence for energy-dependent copper efflux as a mechanism of Cu2+ resistance in the cyanobacterium Nostoc calcicola

Wild-type Nostoc calcicola carried out oxygenic photosynthesis extremely sensitive to copper. A Cu(2+)-resistant mutant (Cu-R1) of the cyanobacterium grew normally at high concentrations of Cu2+. Its ability to grow under such conditions was found to be due to mutational acquisition of an energy-dependent efficient system of Cu(2+)-efflux, which rendered Cu(2+)-inhibited oxygenic photosynthesis fully reversible.