钝顶螺旋藻在不同光照条件下的放氧特性

钝顶螺旋藻在持续照光和中等频率 (0.01~20 Hz) 的光/暗交替照光下的放氧特性对光生物反应器的设计和操作具有重要意义。构建了一套可实现光/暗交替的光生物反应器系统对此进行研究,结果显示：根据与放氧速率的关系,可以将光强分为4个区：光限制区 (0~335 μmol/(m2·s)),过渡区 (335~875 μmol/(m2·s)),光饱和区 (875~2 775 μmol/(m2·s)) 以及光抑制区 (2 775 μmol/(m2·s)以上)。提高光/暗频率能否提高微藻光合速率取决于所采用的光强和     

Photosynthetic efficiency of Chlamydomonas reinhardtii in flashing light

Efficient light to biomass conversion in photobioreactors is crucial for economically feasible microalgae production processes. It has been suggested that photosynthesis is enhanced in short light path photobioreactors by mixing‐induced flashing light regimes. In this study, photosynthetic efficiency and growth of the green microalga Chlamydomonas reinhardtii were measured using LED light to simulate light/dark cycles ranging from 5 to 100 Hz at a light‐dark ratio of 0.1 and a flash intensity of 1000 µmol m⁻² s⁻¹. Light flashing at 100 Hz yielded the same photosynthetic efficiency and specific growth rate as cultivation under continuous illumination with the same time‐averaged light intensity (i.e., 100 µmol m⁻² s⁻¹). The efficiency and growth rate decreased with decreasing flash frequency. Even at 5 Hz flashing, the rate of linear electron transport during the flash was still 2.5 times higher than during maximal growth under continuous light, suggesting storage of reducing equivalents during the flash which are available during the dark period. In this way the dark reaction of photosynthesis can continue during the dark time of a light/dark cycle. Understanding photosynthetic growth in dynamic light regimes is crucial for model development to predict microalgal photobioreactor productivities. Biotechnol. Bioeng. 2011;108: 2905–2913. © 2011 Wiley Periodicals, Inc.     

Effects of light/dark cycle, mixing pattern and partial pressure of H2 on biohydrogen production by Rhodobacter sphaeroides ZX-5

The effects of light/dark cycle, mixing pattern and partial pressure of H₂ on the growth and hydrogen production of Rhodobacter sphaeroides ZX-5 were investigated. The results from light/dark cycle culture showed that little or no hydrogen production was observed during the dark periods, and the hydrogen production immediately recovered once illumination was resumed. Also, it was found that the optimum condition of shaking velocity was 120 rpm for hydrogen photo-fermentation. Meanwhile, shaking during H₂ production phase (i.e., cell growth stationary phase) of photo-fermentation played a crucial role on effectively enhancing the phototrophic hydrogen production, rather than that during cell exponential growth phase. The other factor evaluated was hydrogen partial pressure in the culture system. The substrate conversion efficiency increased from 86.07% to 95.56% along with the decrease of the total pressure in the photobioreactor from 1.082 × 10⁵ to 0.944 × 10⁵ Pa, which indicated that reduction of H₂ partial pressure by lowering the operating pressure substantially improved H₂ production in an anaerobic, photo-fermentation process.     

Specific growth rate of Chlamydomonas reinhardtii and Chlorella sorokiniana under medium duration light/dark cycles: 13–87 s

The specific growth rate of Chlamydomonas reinhardtii and Chlorella sorokiniana decreased under square-wave light/dark cycles of medium duration, 13–87 s, in comparison to continuous illumination. Three experiments were done in three different turbidostats at saturating and sub-saturating light intensities during the light period, 240–630 μmol m⁻² s⁻¹. Within each experiment the light intensity during the light periods of the intermittent light regimes was equal and this intensity was also applied under continuous illumination. The specific growth rate decreased proportional or more than proportional to the fraction of time the algae were exposed to light; this light fraction ranged from 0.32 to 0.88. We conclude that under these light regimes the chlorophyta C. reinhardtii and C. sorokiniana are not able to store light energy in the light period to sustain growth in the dark period at the same rate as under continuous illumination. C. reinhardtii increased its specific light absorbing surface by increasing its chloropyll-a content under light/dark cycles of 13 s duration and a light fraction of 0.67 at 240 μmol m⁻² s⁻¹; the chloropyll-a content was twice as high under intermittent illumination in comparison to continuous illumination. The combination of a higher specific light absorption together with a lower specific growth rate led to a decrease of the yield of biomass on light energy under intermittent illumination.     

深红红螺菌吸氢酶缺失突变株在管式光合反应器中的产氢

本研究设计了一种2 L分体式管式光合反应器, 并研究了深红红螺菌(Rhodospirillum rubrum)吸氢酶缺失突变株在该反应器中分别利用人工光源(持续光照与光暗交替)和自然光的产氢规律。结果表明在人工光照条件下R. rubrum的产氢可维持5 d, 持续光照和光暗交替条件下(12 h: 12 h)的氢产量可分别达到5752 mL/PBR ± 158 mL/PBR和5012 mL/PBR ± 202 mL/PBR; 自然光条件下, 最适产氢光照强度为30000 Lux~40000 Lux; 在此光照条件下, R. rubrum产氢可维持6 d~ 10 d, 最高氢产量可达到2800 mL/PBR。尽管利用自然光的氢产量比利用人工光源氢产量低, 但是利用自然光的产氢比较经济, 并且该光合产氢系统操作简单, 该工艺有望开发为低成本的光合细菌产氢技术。     

Effect of light intensity on Opisthorchis viverrini cercarial shedding levels from Bithynia snails--a preliminary study

Opisthorchis viverrini requires Bithynia snails as the first intermediate host and cyprinid fish as the second intermediate host. Very low natural infection rates have been reported in Bithynia snails, but very high rates have been found in cyprinid fish in the same endemic region. This study investigated the effect of light intensity, the most important stimulus, on the quantity of O. viverrini cercariae shed from naturally infected Bithynia (Digoniostoma) siamensis goniomphalos snails. Snails were evaluated for cercariae output every hour after exposure to various light intensities for a total period of 7 h. The same infected snail was tested under different intensities of light: in the dark, and at 1000, 3000 and 5000 lx. The data showed that under exposure to 1000 and 3000 lx of light, the average percentage and number of cercariae released were higher than that exposed to 5000 lx during the first 2 h of the experiment. In contrast, under higher illumination (5000 lx) a longer time (6 h) was required to stimulate the peak emergence of cercariae. Darkness was not able to induce O. viverrini cercariae emergence. Among the three intensities of light, exposure at 1000 lx induced the highest average number of released cercariae per snail and the highest percentage of cercarial emergence within the first 2 h (125, 54.86%), followed by exposure at 3000 lx (69, 25.58%) and 5000 lx (12, 7.78%). The results suggest that the light intensity of 1000 lx for 2 h would be optimal for O. viverrini cercarial shedding from naturally infected B. (D.) siamensis goniomphalos snails.     

Enhanced algae growth in both phototrophic and mixotrophic culture under blue light

Biomass productivity and fatty acid methyl esters (FAME) derived from intracellular lipid of a Nannochloropsis sp. isolated from Singapore’s coastal waters were studied under different light wavelengths and intensities. Nannochloropsis sp., was grown in both phototrophic and mixotrophic (glycerol as the carbon source) culture conditions in three primary monochromatic light wavelengths, i.e., red, green and blue LEDs, and also in white LED. The maximum specific growth rate (μ) for LEDs was blue > white > green > red. Nannochloropsis sp. achieved a μ of 0.64 and 0.66 d⁻¹ in phototrophic and mixotrophic cultures under blue lighting, respectively. The intracellular fatty acid composition of Nannochloropsis sp. varied between cultures exposed to different wavelengths, although the absolute fatty acid content did differ significantly. Maximum FAME yield from Nannochloropsis sp. was 20.45% and 15.11% of dry biomass weight equivalent under photo- and mixotrophic culture conditions respectively for cultures exposed to green LED (550 nm). However, maximum volumetric FAME yield was achieved for phototrophic and mixotrophic cultures (i.e., 55.13 and 111.96 mg/l, respectively) upon cell exposure to blue LED (470 nm) due to highest biomass productivity. It was calculated that incremental exposure of light intensity over the cell growth cycle saves almost 20% of the energy input relative to continuous illumination for a given light intensity.     

The effects of photoperiod and light intensity on the sporulation of Brazilian and Norwegian isolates of Neozygites floridana

The objective of this study was to determine the effects of light intensity and duration (photoperiod) on the sporulation (discharge of primary conidia) and conidia germination (from non-infective primary conidia to infective capilliconidia) of Neozygites floridana isolates from Tetranychus urticae originating from Norway and Brazil. Two light intensities (40 and 208 μmol m⁻² s⁻¹), three photoperiods (24 h of continuous light (24 h D), 12 h of darkness followed by 12 h of light (12 h D: 12 h L) and 24 h of continuous darkness (24 h D)) and two temperatures (18 °C and 23 °C) were tested. The fungus produced similar amounts of primary conidia and capilliconidia at 12 h D:12 h and 24 h D, indicating that the fungus discharges almost all of its conidia during the first 12 h of darkness. Light had less of an effect on the production of primary conidia than on capilliconidia formation. At 24 h L, capilliconidia formation was significantly lower for all tested light intensities, temperatures and isolates compared to 12 h D:12 h L and 24 h D. At both light intensities, 24 h L resulted in a significantly lower capilliconidia formation for the Norwegian isolate compared to the Brazilian isolate. Our data suggest that, even though 24 h L reduced sporulation, some capilliconidia formation may occur at the low light intensities found on the underside of strawberry leaves during parts of the day as well as the top of a non-shaded strawberry leaf during the dim evening and morning hours in the tropics and during the dim, long summer days in temperate regions.     

Characteristics of a biofilm photobioreactor as applied to photo-hydrogen production

The application of a cell immobilization technique to a biofilm-based photobioreactor was developed to enhance its photo-hydrogen production rate and light conversion efficiency. Rhodopseudomonas palustris CQK 01 was initially attached to the surface of packed glass beads to form a biofilm in this experiment. Then, the biofilm photobioreactor (BPBR) was illuminated by light-emitting diodes with light wavelengths of 470, 590 and 630 nm and hydrogen was evolved with glucose being the sole carbon source. Under the illumination condition of 5000 lux illumination intensity and 590 nm wavelength, the BPBR showed good hydrogen production performance: the hydrogen production rate was 38.9 ml/l/h and light conversion efficiency was 56%, while the hydrogen yield was 0.2 mol H₂/mol glucose. Furthermore, results show that the highest hydrogen production rate and glucose removal rate were obtained when the glucose concentration is 0.12 M, the optimal pH 7 and optimal temperature of influent liquid 25 °C.     

Improvement of carbon dioxide biofixation in a photobioreactor using Anabaena sp. PCC 7120

The biological photosynthetic process is useful and environmentally benign compared with other carbon dioxide (CO₂) mitigation processes. In the present study, Anabaena sp. PCC 7120 was utilized for carbon dioxide mitigation. A customized airlift photobioreactor was found to provide higher light utilization efficiency and a higher rate of CO₂ biofixation compared with that of a bubble column. The maximum biomass concentrations were 0.71 and 1.13 g L^?1 in the bubble column and airlift photobioreactor, respectively, using BG11₀ medium under aerated conditions. A lower mixing time in the airlift photobioreactor compared with that of the bubble column resulted in improved mass transfer. The CO₂ biofixation rate of Anabaena sp. PCC 7120 was determined using different phosphate concentrations at a light intensity of 120 μE m^?2 s^?1 and 5% (v/v) CO₂-enriched air in the airlift photobioreactor. However, it was observed that the specific growth rate was independent at higher light intensity. In addition, it was observed that increased light intensity, phosphate and CO₂ concentrations could enhance the CO₂ biofixation efficiency to a greater extent.     

Effect of light/dark cycles on wastewater treatments by microalgae

Chlorella kessleri was cultivated in artificial wastewater using diurnal illumination of 12 h light/12 h dark (L/D) cycles. The inoculum density was 10⁵ cells/mL and the irradiance in light cycle was 45 μmol m² s⁻¹ at the culture surface. As a control culture, another set of flasks was cultivated under continuous illumination. Regardless of the illumination scheme, the total organic carbon (TOC) and chemical oxygen demand (COD) was reduced below 20% of the initial concentration within a day. However, cell concentration under the L/D lighting scheme was lower than that under the continuous illuminating scheme. Thus the specific removal rate of organic carbon under L/D cycles was higher than that under continuous illumination. This result suggested thatC. kessleri grew chemoorganotrophically in the dark periods. After 3 days, nitrate was reduced to 136.5 and 154.1 mg NO₃ ⁻-N/L from 168.1 mg NO₃ ⁻-N/L under continuous illumination and under diurnal cycles, respectively. These results indicate nitrate removal efficiency under continuous light was better than that under diurnal cycles. High-density algal cultures using optimized photobioreactors with diurnal cycles will save energy and improve organic carbon sources removal.     

Lumostatic strategy for microalgae cultivation utilizing image analysis and chlorophyll a content as design parameters

Cultivation of microalgae Chlorella sp. was performed in draft-tube photobioreactors. Effect of light intensity on the microalgae growth performance was conducted under a light intensity range of 82-590 μmol/m² s. A lumostatic strategy was proposed based on the light distribution profiles obtained by image analysis and specific chlorophyll a content. The proposed lumostatic strategy allowed a maximum biomass dry weight of 5.78 g/L and a productivity of 1.29 g/L d, which were 25.7% and 74.3% higher than that achieved by the optimal constant light intensity, respectively. A comparison with other lumostatic strategies reported in the literature indicated that the proposed lumostatic strategy in the current study can be a promising approach in improving the growth of microalgae.     

Vertical tubular photobioreactor for semicontinuous culture of Cyanobium sp

We evaluated the kinetic culture characteristics of the microalgae Cyanobium sp. grown in vertical tubular photobioreactor in semicontinuous mode. Cultivation was carried out in vertical tubular photobioreactor for 2 L, in 57 d, at 30 °C, 3200 Lux, and 12 h light/dark photoperiod. The maximum specific growth rate was found as 0.127 d⁻¹, when the culture had blend concentration of 1.0 g L⁻¹, renewal rate of 50%, and sodium bicarbonate concentration of 1.0 g L⁻¹. The maximum values of productivity (0.071 g L⁻¹ d⁻¹) and number of cycles (10) were observed in blend concentration of 1.0 g L⁻¹, renewal rate of 30%, and bicarbonate concentration of 1.0 g L⁻¹. The results showed the potential of semicontinuous cultivation of Cyanobium sp. in closed tubular bioreactor, combining factors such as blend concentration, renewal rate, and sodium bicarbonate concentration.     

Hydrogen production by Rhodopseudomonas palustris WP 3-5 in a serial photobioreactor fed with hydrogen fermentation effluent

In this study, a lab-scale serial photobioreactor composed of three column reactors was constructed and continuously operated to investigate several parameters influencing photohydrogen production when using the synthetic wastewater and the anaerobic hydrogen fermentation effluents as the influents. The results indicated that better hydrogen production rate was obtained when the serial photobioreactor was operated under cellular recycling at a short HRT of 8 h. The serial photobioreactor maintained high hydrogen content ca. 80% in the produced gas and 0.4× dilution ratio was the suitable ratio for hydrogen production. When the photobioreactor fed with the real wastewater (Effluent 1) containing 100 mg/L NH₄Cl, Column 1 reactor successfully reduced ammonia concentration to about 60 mg/L for cell synthesis, resulting in a steady hydrogen production in the following two column reactors. The average hydrogen production rate was 205 mL-H₂/L/d.     

Luminostat operation: a tool to maximize microalgae photosynthetic efficiency in photobioreactors during the daily light cycle?

The luminostat regime has been proposed as a way to maximize light absorption and thus to increase the microalgae photosynthetic efficiency within photobioreactors. In this study, simulated outdoor light conditions were applied to a lab-scale photobioreactor in order to evaluate the luminostat control under varying light conditions. The photon flux density leaving the reactor (PFD_out) was varied from 4 to 20 μmol photons m⁻² s⁻¹and the productivity and photosynthetic efficiency of Chlorella sorokiniana were assessed.Maximal volumetric productivity (1.22 g kg⁻¹ d⁻¹) and biomass yield on PAR photons (400-700 nm) absorbed (1.27 g mol⁻¹) were found when PFD_out was maintained between 4 and 6 μmol photons m⁻² s⁻¹. The resultant photosynthetic efficiency was comparable to that already reported in a chemostat-controlled reactor. A strict luminostat regime could not be maintained under varying light conditions. Further modifications to the luminostat control are required before application under outdoor conditions.     

5种光周期对锦鲤生长、能量收支及生物钟基因表达的影响

研究不同光照周期(长光照18L﹕6D、短光照8L﹕16D、连续光照24L﹕0D、连续黑暗0L﹕24D和对照组12L﹕12D)条件对锦鲤(Cyprinus carpio)生长、能量收支及生物钟基因相对表达量的影响, 实验周期为90d。结果表明, 在整个试验周期, 各光周期处理组成活率无显著变化(P＞0.05), 24L组和18L﹕6D组饲料系数显著低于12L﹕12D组、8L﹕16D组和24D组(P＜0.05)。终末体重、特定生长率在实验前30d内受光照影响不大(P＞0.05), 而实验30d后出现显著变化, 延长光周期尤其是连续光照会显著增加终末体重和特定生长率(P＜0.05); 对比连续黑暗0L﹕24D组, 其他光周期处理组锦鲤摄食能分配在代谢和生长的比例显著增加(P＜0.05); 4个生物钟相关Clock、Per2、Cry1和Bmal1基因相对表达水平无明显规律。综上所述, 延长光照时间, 尤其是连续光照有利于锦鲤幼鱼的生长和发育。     

The light/dark cycle operation with an hour-scale period enhances caffeine production by Coffea arabica cells

The intermittent light irradiation with an hour-scale period is used for producing caffeine by Coffea arabica cells. Three factors concerning the light/dark cycle operation such as light intensity, the length of the cycle (period), and the ratio of the illumination time to the dark time (light/dark ratio) were investigated to optimize the caffeine production efficiency regarding light consumption. The light/dark ratio of 1/1 enhanced caffeine production, reaching the same level as continuous light; thus, the intermittent light irradiation improved the production efficiency twofold. The production was not influenced by the period, but was determined by light intensity regardless of intermittent or continuous light irradiation.     

Effect of photoperiod manipulation on the growth performance of juvenile lenok,Brachymystax lenok (Pallas, 1773)

The effect of four different light regimes on growth was studied in lenok, Brachymystax lenok. Fish with average weights of 5.5 g were subjected to four different photoperiods (0L:24D, 6L:18D, 12L:12D and 24L:0D) for 35 days. The specific growth rate (SGR) of lenok in 24‐h darkness had a significantly higher SGR than those in the continuous light regime (P < 0.05); however, there was no significant difference among fish exposed to 6L:18D, 12L:12D and 24L:0D photoperiods. There was a tendency for higher food intake over the light period extension from 0L to 24L, and feed intake was significantly higher in the continuous light group than in 24‐h darkness (P < 0.05). No significant difference in feed conversion efficiency (FCE) was observed between fish exposed to 0L:24D and 6L:18D photoperiods, however, the FCE in both photoperiods was significantly higher than that in the other two groups. The final survival rate of juveniles varied from 79.67 to 95.33%, with significant differences among experimental groups. Fish tested in continuous illumination spent much more energy on respiration and excretion while depositing less energy for growth than in the other photoperiods. In contrast, fish in 24‐h darkness deposited more energy for growth and spent less energy on respiration and excretion. Results show that photoperiod manipulation can affect growth, and that a continuous dark regime could improve growth in lenok at this stage of development.     

Effect of light intensity on broiler behaviour and diurnal rhythms

Light intensity manipulation is an important management tool affecting broiler behaviour and physiology but still there is a debate regarding the optimum level to be used in confinement barns. Two experiments were completed to study the impact of light intensity (1, 10, 20 and 40 lx) on behaviour and diurnal rhythms of broilers raised to 35 d of age. For each experiment, 950 Ross × Ross 308 chicks were housed per room with replication of individual light intensity treatment in two environmentally controlled rooms. Within each large room, a small pen with 25 male and 25 female chicks was used for recording behaviour. Data were analyzed as a randomized complete block design with experiment acting as a block. All chicks were provided with 40 lx intensity and 23 h light until shifting to treatment light intensity and 17 h daylength at 7 d of age. For each replicate, behaviour was recorded for a 24 h period, starting at 16 or 17 d of age. At 23 d of age, three birds per room were bled at the start, middle and end of light and dark periods for melatonin estimation using RIA. When summarized over the 24 and 17 h observation periods, birds exposed to a light intensity of 1 lx rested more (P = 0.01) and preened (P < 0.05) and foraged (P < 0.05) less in comparison to other light intensities. Birds from all treatments exhibited diurnal rhythms for feeding, resting, drinking, walking, standing, foraging and preening behaviours with little or no activity during the 7 h dark phase. The serum melatonin levels at the start, middle and end of light and dark phases were unaffected by light intensity (P > 0.1). In conclusion, light intensity ranges from 1 to 40 lx did not affect melatonin levels or behavioural diurnal rhythms, but birds exposed to a light intensity of 1 lx rested more and preened less, potentially indicating a reduced welfare state.     

Circadian and Seasonal Responses in Indian Weaver Bird: Subjective Interpretation of Day and Night Depends Upon Both Light Intensity and Contrast Between Illuminations

This study investigated whether changes in illumination modify perception of day and night conditions in a diurnal species, the Indian weaver bird. Birds were initially subjected to a 12-h light:12-h dark regime (12L:12D; L?=?20 lux, D =?0.5 lux). After every 2 wks, the combinations of light illumination in L and D phases were changed as follows: 20:2 lux, 20:5 lux, 20:10 lux, 20:20 lux, 20:100 lux, and 20:200 lux. Finally, birds were released into dim constant light (0.5 lux) for 2 wks to determine the phase and period of the circadian activity rhythm. They were also laparotomized at periodic intervals to examine the effects of the light regimes on the seasonal testicular cycle. All individuals showed a consistently similar response. As evident by the activity pattern under these light regimes, both in total activity during contrasting light phases and during the 2?h in the beginning and end of first light phase, birds interpreted the period of higher light intensity as day, and the period of lower intensity as the night. During the period of similar light intensity, i.e., under LL, birds free-ran with a circadian period (～24?h). In bright LL (20 lux), the activity rhythm was less distinct, but periodogram analysis revealed the circadian period for the group as 24.46?±?0.41?h (mean?±?SE). However, in dim LL at the end of the experiment, all birds exhibited a circadian pattern with average period of 25.52?±?0.70?h. All birds also showed testicular growth and regression during the 16-wks study. It is suggested that weaver birds interpret day and night subjectively based on both the light intensity and contrast between illuminations during two phases over the 24?h. (Author correspondence: drskumar7@yahoo.com)