Proton release during successive oxidation steps of the photosynthetic water oxidation process: stoichiometries and pH dependence.

Flash-induced absorption changes of pH-indicating dyes were investigated in photosystem II enriched membrane fragments, in order to retrieve the individual contributions to proton release of the successive transitions of the Kok cycle. These stoichiometric coefficients were found to be, in general, noninteger and to vary as a function of pH. Proton release on the S0----S1 step decreases from 1.75 at pH 5.5 to 1 at pH 8, while, on S1----S2 the stoichiometry increases from 0 to 0.5 in the same pH range and remains close to 1 for S2----S3. These findings are analyzed in terms of pK shifts of neighboring amino acid residues caused by electrostatic interactions with the redox centers involved in the two first transitions. The electrochromic shift of a chlorophyll, associated with the S transitions, responding to local electrostatic effects was investigated under similar conditions. The pH dependence of this signal upon the successive transitions was found correlated with the titration of the proton release stoichiometries, expressing the electrostatic balance between the oxidation and deprotonation processes.     

Effect of pH on growth of acid stream algae

Five species of algae (Chlamydomonas applanata var. acidophila, Euglena mutabilis, Gloeochrysis turfosa, Hormidium rivulare, Stichococcus bacillaris) were isolated from a stream at pH 2·6–3·1, and their laboratory growth studied. Growth of all species could occur at pH values lower than those from which they were isolated, the lowermost limits being quite similar to those recorded for the particular species growing anywhere in England. Morphological differences were apparent with all five species at the lowermost pH values. These took place with Stichococcus bacillaris at pH values at which there was little reduction in growth rate, but with the other species obvious differences in morphology were correlated with a marked reduction in growth rate below the optimum rate. At the uppermost pH value tested, however, no obvious morphological differences were apparent. The effect of including 10% stream water in the medium was rather similar for all five species. No influence on growth rate was detectable at the lower pH values, but higher pH values led to a decrease in growth rate as compared with that found in medium lacking stream water.     

Effects of pH and temperature on growth ofSaprolegnia diclina andS. parasitica isolated from various sources

Saprolegnia diclina andS. parasitica isolated from three sources could germinate in strong acidic conditions. Growth ability correlated with the species of fungi rather than with the sources from which they were isolated.S.diclina isolates appeared to germinate at a pH condition as low as 3.5, whereasS. parasitica isolates could not germinate at below pH 3.8.S. parasitica isolates from visceral mycoses still showed good growth at 30°C, whereas other isolates did not. Also,S. parasitica isolates from visceral mycoses produced more abundant motile zoospores, and continued to do so for a longer period of time (28 d), thanS. parasitica isolates from external saprolegniasis andS. diclina isolates.     

Algal growth on organic compounds as nitrogen sources

Two experimental series were run to evaluate the potential of algal development on dissolved organic nitrogen (DON) compounds as the sole source of nitrogen (N) nutrition. Monocultures of several common Lake Kinneret algae (Pediastrum duplex, Synechococcus sp., Microcystis aeruginosa, Aphanizomenon ovalisporum and Cyclotella sp.) were incubated for 3 weeks in the laboratory with different inorganic (NH4⁺, NO3^-) or organic (hypoxanthine, urea, guanine, ornithine, glucosamine, lysine) nitrogen sources. Even though the cultures were not axenic, marked differences were observed in algal growth response. Pediastrum, Cyclotella and Aphanizomenon grew well on most N sources, and cyanobacterial growth and yield were consistently greatest when the urea was the only N source. We also followed algal growth and eventual species dominance in batch samples of GF/F-filtered lake water, supplemented with orthophosphate and different inorganic or organic N compounds and inoculated with concentrated lake phytoplankton. Although no clear impact on phytoplankton growth (as chlorophyll concentration) was observed, in seven out of 11 experiments we could discern changes in the algal species that became dominant in flasks with different organic and inorganic N sources. Our results are consistent with the proposition that components of the DON pool are not only an important potential, direct or indirect N source for phytoplankton, but also that different algal species can exploit these sources with varying capabilities so that different N substrates may selectively stimulate the development of dominant algal species.      

Effect of anaerobiosis on photosynthetic reactions and nitrogen metabolism of algae with and without hydrogenase

Summary The effect of anaerobic (N₂+CO₂) pre-incubation in the dark on photosynthetic reactions (O₂ evolution, measured manometrically and with the oxygraph; fluorescence; and photoproduction of H₂, measured with the mass spectrometer) was studied in algae with hydrogenase (strains of Chlorella fusca, C. kessleri, C. vulgaris f. tertia, and Ankistrodesmus braunii) and in algae without hydrogenase (strains of Chlorella vulgaris, C. saccharophila, and C. minutissima).The inhibition by anaerobic incubation of photosynthetic O₂ evolution is much stronger in algae without hydrogenase than it is in algae with hydrogenase. The effect of anaerobiosis is most pronounced at rather low light intensity (about 1000 lux), in acid medium (pH 4), and after prolonged anaerobic incubation in the dark (about 20 h). These results indicate that the presence of hydrogenase might be ecologically advantageous for algae under certain conditions.Chlorophyll fluorescence showed the fastest response to anaerobic incubation, and the most pronounced difference between algae with and without hydrogenase. After only 30 min under N₂+CO₂, fluorescence in algae with hydrogenase starts with a peak and decreases within 10 to 20 sec to a rather low steady-state level which is only slightly higher than that found under aerobic conditions. In algae without hydrogenase, fluorescence is rather low during the first 1 to 2 sec and then rises to a higher steady-state level which is much higher than that of the aerobic controls. This indicates an inhibition due to anaerobiosis of photosystem II in algae without hydrogenase.Algae with hydrogenase can react in different ways during the first minutes of illumination. In some cases there is an immediate photoproduction of H₂, which is followed after a few minutes by photosynthetic O₂ evolution; in other algae there is a simultaneous production of H₂ and O₂ from the very beginning; in a few experiments there was no photoproduction of H₂ at all, and in this case there was no photosynthetic O₂ evolution either. Thus, photoproduction of H₂ seems to be the process which normally enables algae with hydrogenase to oxidise and thereby activate their photosynthetic electron transport system after anaerobic incubation.A mass spectrometric search for nitrogen fixation (using N₂ and acetylene) in eucaryotic green algae gave negative results, even with species containing hydrogenase and under anaerobic conditions.     

Effects of nitrogen and phosphorus imbalance on photosynthetic traits of poplar Oxford clone under ozone pollution

Ozone (O₃) pollution and the availability of nitrogen (N) and phosphorus (P) in the soil both affect plant photosynthesis and chlorophyll (Chl) content, but the interaction of O₃ and nutrition is unclear. We postulated that the nutritional condition changes plant photosynthetic responses to O₃. An O₃-sensitive poplar clone (Oxford) was subject to two N levels (N0, 0 kg N ha^??1; N80, 80 kg N ha^??1), two P levels (P0, 0 kg P ha^??1; P80, 80 kg P ha^??1) and three levels of O₃ exposure (ambient concentration, AA; 1.5?×?AA; 2.0?×?AA) over a growing season in an O₃ free air controlled exposure (FACE) facility. The daily change of leaf gas exchange and dark respiration (R_d) were investigated at mid-summer (August). Chl a fluorescence was measured three times in July, August and September. At the end of the growing season, Chl content was measured. It was found that Chl content, the maximum quantum yield (F_v/F_m), Chl a fluorescence performance index (PI) and gas exchange were negatively affected by elevated O₃. Phosphorus may mitigate the O₃-induced reduction of the ratio of photosynthesis to stomatal conductance, while it exacerbated the O₃-induced loss of F_v/F_m. Nitrogen alleviated negative effects of O₃ on F_v/F_m and PI in July. Ozone-induced loss of net photosynthetic rate was mitigated by N in medium O₃ exposure (1.5?×?AA). However, such a mitigation effect was not observed in the higher O₃ level (2.0?×?AA). Nitrogen addition exacerbated O₃-induced increase of R_d suggesting an increased respiratory carbon loss in the presence of O₃ and N. This may result in a further reduction of the net carbon gain for poplars exposed to O₃.     

氮源类型和水平对3株球状绿藻生长、油脂和花生四烯酸积累的影响

【背景】缺刻叶球藻(Lobosphaera incisa Reisigl)是一种单细胞球状绿藻,是已知花生四烯酸(Arachidonic acid,AA)含量最丰富的植物资源之一。然而目前其分类和命名仍然较为混乱。【目的】明确3株球状绿藻(SAG2468、SAG2043、H4301)的分类地位及在不同氮源(硝酸钠、尿素、碳酸氢铵、碳酸铵、硝酸铵、氯化铵和硫酸铵)和氮浓度(18mmol/L,3mmol/L)条件下油脂和AA积累的特性。【方法】通过分子系统学和形态观察的方法对3株球状绿藻进行分类界定;采用干重法、重量法和气相色谱分析的方法分别对其生物量、油脂含量、脂肪酸组成及AA含量进行测定。【结果】3株球状绿藻均隶属于叶球藻属(Lobosphaera),SAG2468原定名为缺刻缘绿藻(Parietochloris incisa),现修订为缺刻叶球藻(Lobosphaera incisa),与H4301为缺刻叶球藻的不同地理株系。SAG2043原定名为双隔蚁形藻(Myrmecia bisecta),现修订为双隔叶球藻(Lobosphaera bisecta)。3株微藻在高氮(18 mmol/L)和低氮(3 mmol/L)浓度的硝酸钠和尿素培养条件下均可良好生长,铵盐对藻细胞生长普遍有抑制作用,且浓度越高抑制作用越显著。低氮胁迫能显著促进油脂和AA的积累(P0.05),SAG2043在3 mmol/L硝酸钠条件下油脂和AA产率最高,分别为142.15mg/(L·d)和35.51mg/(L·d),明显高于另外2株微藻(P0.05)。此时SAG2043对应获得的生物量为4.9 g/L,油脂含量为43.49%,AA含量高达干重的10.86%,占总脂肪酸含量的31.75%。【结论】SAG2043是一株更具AA开发潜力的微藻。     

The utilization of organic nitrogen for growth of algae: physiological aspects

The ability of 27 algae belonging to 11 taxonomic divisions to grow at the expense of organic nitrogen was tested in axenic culture. Experiments were carried out in buffered media: morpholine propanesulphonic acid (MOPS) was used successfully for all fresh water strains except diatoms. It was not used as a nitrogen source by any strain examined but served as a good source of sulphur for four strains. The range of substrates used was extensive and included amino acids, urea, acetamide, urate and some nucleosides. Growth rates varied widely but growth yields were generally comparable to those attained with nitrate or ammonia except for substrates containing more than one utilizable nitrogen atom. Limited experiments were carried out in the dark, and it was found that a given substrate was equally suitable for both dark heterotrophic and photolithotrophic growth. Levels of chlorophyll a were measured during growth of two algae with nitrate, glycine and urate. With nitrate, levels of specific chlorophyll a declined some ten-fold during growth: with poor substrates supporting only slow growth, levels were more uniform but were only 10–15% of those attained during growth with good substrates. One strain grown with MOPS as sole source of sulphur produced cultures with levels of chlorophyll a about half those found in sulphate-grown cultures. Tolerance of sodium chloride was examined in a few strains and even putatively fresh water strains were found to be appreciably tolerant.     

Pure culture growth of ectomycorrhizal fungi on inorganic nitrogen sources

Four ectomycorrhizal fungi were tested for their ability to grow (i.e., mycelial mat radial extension and fungal biomass) on nutrient media either supplemented with ammonium-nitrogen or nitrate-nitrogen or in the absence of an inorganic nitrogen source.Pisolithus tinctorius, Cenococcum geophilum andThelephora terrestris exhibited greater growth on ammonium-nitrogen.Suillus granulatus grew better on the nitrate-nitrogen nutrient medium. Regardless of inorganic nitrogen form preference (i.e., ammonium-nitrogen or nitrate-nitrogen), all 4 species showed some growth on each of the 3 nutrient media. Growth rate maxima varied by fungal species as well as by inorganic nitrogen source. Maximum growth rate forT. terrestris exceeded rates exhibited by the other 3 fungi by 2–5 times.     

有机碳源和氮源对三角褐指藻生长的影响

研究了8种有机碳源和4种氮源对三角褐指藻(Phaeodactylum tricornutum)生长的影响.结果表明,三角褐指藻具有兼养生长的能力,碳浓度为5mmol/L和50mmol/L时,葡萄糖、果糖、乙酸钠和甘油对其生长有明显的促进作用,乳酸钠和乙醇抑制藻细胞生长,半乳糖和柠檬酸钠对其生长随有机碳浓度而异.甘油、葡萄糖和乙酸钠的适宜浓度范围分别为5 -800mmol/L、100 -400mmol/L和50 -300mmol/L.培养液中分别加入50mmol/L甘油、400mmol/L葡萄糖和150mmol/L乙酸钠,培养第14天,三角褐指藻的最大生物量分别为对照的1.45倍、1.25倍和1.11倍.甘油兼养生长的最优氮源是尿素,适宜浓度范围为0.88-8.8mmol/L.当尿素浓度为4.4mmol/L时,最高生物量可达1.31g/L.     

Cyclic variations in nitrogen uptake rate of soybean plants: effects of pH and mixed nitrogen sources.

To determine if the daily pattern of NO3- and NH4+ uptake is affected by acidity or NO3- : NH4+ ratio of the nutrient solution, non-nodulated soybean plants (Glycine max) were exposed for 21 days to replenished, complete nutrient solutions at pH 6.0, 5.5, 5.0, and 4.5 which contained either 1.0 mM NH4+, 1.0 mM NO3- [correction of NO3+], 0.67 mM NH4+ plus 0.33 mM NO3- (2:1 NH4+ : NO3-) [correction of (2:1 NH3+ : NO4-)], or 0.33 mM NH4+ plus 0.67 mM NO3- (1:2 NH4+ : NO3-). Net uptake rates of NH4+ and NO3- were measured daily by ion chromatography as depletion from the replenished solutions. When NH4+ and NO3- were supplied together, cumulative uptake of total nitrogen was not affected by pH or solution NH4+ : NO3- ratio. The cumulative proportion of nitrogen absorbed as NH4+ decreased with increasing acidity; however, the proportional uptake of NH4+ and NO3- was not constant, but varied day-to-day. This day-to-day variation in relative proportions of NH4+ and NO3- absorbed when NH4+ : NO3- ratio and pH of solution were constant indicates that the regulatory mechanism is not directly competitive. Regardless of the effect of pH on cumulative uptake of NH4+, the specific nitrogen uptake rates from mixed and from individual NH4+ and NO3- sources oscillated between maxima and minima at each pH with average periodicities similar to the expected interval of leaf emergence.     

Sensitivity analysis of stoichiometric networks: an extension of metabolic control analysis to non-steady state trajectories

A sensitivity analysis of general stoichiometric networks is considered. The results are presented as a generalization of Metabolic Control Analysis, which has been concerned primarily with system sensitivities at steady state. An expression for time-varying sensitivity coefficients is given and the Summation and Connectivity Theorems are generalized. The results are compared to previous treatments. The analysis is accompanied by a discussion of the computation of the sensitivity coefficients and an application to a model of phototransduction.     

Calorimetric and stoichiometric analysis of growth of Kluyveromices fragilis in continuous culture: nitrogen limitation imposed upon carbon-limited growth

The calorimetric response of the yeast Kluyveromices fragilis was investigated for growth in continuous culture where nitrogen limitation was imposed on a carbon-limited culture. Calorimetric measurements were combined with off gas analysis, measurements of biomass, substrate and product concentrations, elemental biomass composition, and heat production to study the physiological response of K. fragilis. Regions where both carbon and nitrogen limited growth, were found over a broad range of dilution rates and feed carbon-to-nitrogen ratios. The principle mechanism by which K. fragilis accommodated regions of dual carbon and nitrogen limitation was by partial decoupling of the anabolic and catabolic pathways. When the culture was only nitrogen-limited, increased decoupling of the two pathways was observed. The principal effect of the decoupling was an increased catabolic consumption of glucose, generating an increased heat yield. The preferred way to process the excess glucose was through respiration but the cells were also capable of fermenting a small percentage of the excess glucose in specific cases where the dissolved oxygen partial pressure approached zero. In addition, these results were qualitatively compared to similar studies on Saccharomices cerevisiae. The two yeasts were similar in their ability to accommodate dual limitation by uncoupling anabolic biomass formation from substrate consumption. The two yeasts were dissimilar in how the catabolic substrate was processed. For S. cerevisiae the presence of a bottleneck in the respiration pathway dictated that the majority of the catabolic glucose consumption was by fermentation. For K. fragilis, the lack of a bottleneck in the respiration pathway dictated that the majority of catabolic glucose substrate consumption was by respiration.     

Effect of various carbon and nitrogen sources on cellulose synthesis by Acetobacter xylinum

The effect of various carbon and nitrogen sources on cellulose membrane production by Acetobacter xylinum was evaluated. Among the carbon sources, sucrose, glucose and mannitol were found to be suitable for optimum levels of cellulose production. The strain was able to utilize a wide range of protein and nitrogen sources such as peptone, soybean meal, glycine, casein hydrolysate, and glutamic acid for cellulose synthesis. Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) analysis of pellicle proteins (PP) revealed electrophoretic bands of molecular masses in the range of 116–20 kDa. Furthermore, the strain can be useful for the removal of various nitrogenous and carbon substrates present in waste waters.     

The influence of various carbon and nitrogen sources on oil production byFusarium oxysporum

The oil-synthesizing capacityof Fusarium oxysporum, cultivated on basal nutrient medium, was evaluated using different carbon and nitrogen sources. In one of the media, molasses was also used as a principal carbon source. Media containing glucose and ammonium nitrate were found to be most efficient for oil production. Fatty acid profile of the fungal oil indicated the presence of a wide range of fatty acids ranging from C₈ to C₂₄. Fatty acid composition largely depends on the type of carbon and nitrogen sources.     

氮源对谷氨酰胺转胺酶合成的影响

研究不同氮源及培养条件对轮枝链霉菌 (Streptoverticillium)SK - 1合成谷氨酰胺转胺酶 (TGase)的影响 ,结果当以 5 0g/L玉米浆为主要氮源时发酵酶活水平可达 3 0 1μmol/ (min·ml) ;对摇瓶发酵条件进行优化后 ,以 5 0g/L玉米浆为主要氮源 ,起始pH值为 7 0～ 7 5 ,培养温度为 30℃ ,接种量范围为 5 % - 10 % ,培养时间为 38h时 ,酶活最高可达 4 5 2 μmol/ (min·ml) ,酶活提高了5 0 17%。玉米浆作为氮源时发酵酶活比较高 ,发酵时间也较短 ,酶的生产成本较低     

Heterotrophic production of biomass and lutein by Chlorella protothecoides on various nitrogen sources

The effects of nitrate, ammonium, and urea as nitrogen sources on the heterotrophic growth of Chlorella protothecoides were investigated using flask cultures. No appreciable inhibitory effect on the algal growth was observed over a nitrogen concentration range of 0.85-1.7 g l(-)(1). In contrast, differences in specific growth rate and biomass production were found among the cultures with the various nitrogen compounds. The influence of different nitrogen sources at a concentration equivalent to 1.7 g l(-)(1) nitrogen on the heterotrophic production of biomass and lutein by C. protothecoides was investigated using the culture medium containing 40 g l(-)(1) glucose as the sole carbon and energy source in fermentors. The maximum biomass concentrations in the three cultures with nitrate, ammonium, and urea were 18.4, 18.9, and 19.6 g l(-)(1) dry cells, respectively. The maximum lutein yields in these cultures were between 68.42 and 83.81 mg l(-)(1). The highest yields of both biomass and lutein were achieved in the culture with urea. It was therefore concluded that urea was the best nitrogen source for the production of biomass and lutein. Based on the experimental results, a group of kinetic models describing cell growth, lutein production, and glucose and nitrogen consumption were proposed and a satisfactory fit was found between the experimental results and predicted values. Dynamic analysis of models demonstrated that enhancing initial nitrogen concentration in fermentor cultures, which correspondingly enhances cell growth and lutein formation, may shorten the fermentation cycle by 25-46%.