Photoheterotrophy and chemoheterotrophy among unicellular blue-green algae

Summary Thirty eight axenic strains belonging to the Chroococcales were screened for the ability to grow photoheterotrophically in the light with glucose in the presence of 10^-5 M DCMU, which inhibits photoautotrophic growth. Seven strains could do so, and four of them could also grow chemoheterotrophically, though more slowly, with glucose in the dark. Six are members of the genus Aphanocapsa and one of the genus Chlorogloea. The remaining 31 strains examined appear to be obligate photoautotrophs. A quantitative study of the growth behaviour of one strain, Aphanocapsa 6714, fully confirmed its facultative photoheterotrophy and chemoheterotrophy.     

高温胁迫下不同光强对‘赤霞珠’葡萄PSII活性及恢复的影响

本文研究了高温与不同光强结合处理对‘赤霞珠’葡萄叶片PSII活性及恢复的影响。结果表明,高温黑暗处理（40℃,0μmaol·m-2．s-1）导致叶片PSII最大光化学效率（Fv/Fm）、反应中心吸收的光能用于电子传递的量子产额（ψEo）与单位反应中心光能的传递（ETo/RC）降低明显,且无恢复趋势,K点相对荧光（Vk）、单位反应中心光能的吸收（ABS／RC）与捕获（TRo／RC）显著升高。高温弱光处理（40℃,200μmol·m-2．s-1）后的叶片PSII活性明显恢复,ETo／RC降低明显,TRo/RC无显著变化。高温强光（40℃,1600μmol·m-2．S-1）处理导致单位面积有活性反应中心数量（RC/CSm）抑制程度最大,恢复程度较低。实验结果说明,高温处理下黑暗对葡萄PSII功能活性及恢复均会造成抑制,而弱光可以显著缓解高温对葡萄叶片的胁迫作用,并促进PSII的恢复,强光导致胁迫下的PSII功能抑制最明显。     

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.     

Weak red light plays an important role in awakening the photosynthetic machinery following desiccation in the subaerial cyanobacterium Nostoc flagelliforme

The subaerial cyanobacterium Nostoc flagelliforme can survive for years in the desiccated state and light exposure may stimulate photosynthetic recovery during rehydration. However, the influence of light quality on photosynthetic recovery and the underlying mechanism remain unresolved. Exposure of field collected N. flagelliforme to light intensity ≥2 μmol photons m⁻² s⁻¹ showed that the speed of photosystem II (PSII) recovery was in the following order: red > green > blue ≈ violet light. Decreasing the light intensity showed that weak red light stimulated PSII recovery during rehydration. The chlorophyll fluorescence transient and oxygen evolution activity indicated that the oxygen evolution complex (OEC) was the activated site triggered by weak red light. The damaged D1 protein accumulated in the thylakoid membrane during dehydration and is degraded and resynthesized during dark rehydration. PsbO interaction with the thylakoid membrane was induced by weak red light. Thus, weak red light plays an important role in triggering OEC photoactivation and the formation of functional PSII during rehydration. In its arid habitats, weak red light could stimulate the awakening of dormant N. flagelliforme after absorbing water from nighttime dew or rain to maximize growth during the early daylight hours of the dry season.     

GERMINATION AND GROWTH OF CELOSIA CRISTATA L., UNDER VARIOUS LIGHT AND TEMPERATURE REGIMES

Continuous light or alternating light and dark appear to be necessary for good germination of Celosia cristata L. As temperature increased up to 31 C so did germination; thereafter, it decreased. There appears to be a preference for high constant or high alternating temperatures in germination. As light intensity decreased so did growth in terms of leaf area, dry weight and relative growth rate. Proportionally more leaf is also made and leaf:area ratio increased. However, root weight ratio decreased. Although both high light intensity and high temperature are required for the good growth of Celosia, temperature appeared to be more important than light. A reduction of less than one-third of full light may not cause a significant reduction in growth. The results explain the observed differences in the nature of C. cristata in the field as well as its distributional limits.     

PHYSIOLOGICAL RESPONSES DURING DARK SURVIVAL AND RECOVERY IN AUREOCOCCUS ANOPHAGEFFERENS (PELAGOPHYCEAE)1

The harmful bloom alga Aureococcus anophagefferens Hargraves et Sieburth can survive prolonged darkness, which could facilitate overwinter survival and dispersal by anthropogenic vectors such as ballast water. Experiments were conducted to examine the biochemical and photosynthetic changes in cells during dark storage. Cells were stored in the dark for periods from 2 to 14 days and were sampled at days 0, 1, 2, 4, 7, 10, and 14. Samples from days 2, 7, and 14 were monitored during a recovery period of 4–5 days. Physiological and photosynthetic parameters were measured during the dark storage and recovery periods. Cultures resumed growth quickly when returned to light, and bacterial counts remained constant during the dark storage period but increased rapidly during recovery periods. Cellular protein, carbohydrate, and lipid concentrations declined slightly during the dark period. There were no changes in chl a per cell or in RUBISCO per cell during 14 days of darkness. The data therefore suggest that A. anophagefferens is able to maintain its photosynthetic apparatus during dark storage periods of at least 2 weeks and relies on cellular reserves until it is returned to light to resume photosynthesis. During the recovery period in the light, the cells are able to acclimate rapidly to current light levels and resume growth.     

Light quality effects on subsequent dark 14CO2-fixation in Fucus serratus

The intensity and fate of ¹⁴CO₂-fixation in the dark are studied on Fucus serratus apices previously maintained under low illumination conditions using white, blue, red or yellow isoquantic lights.In the case of a 180 s pulse, light quality affected dark carbon-fixation, with a higher level of incorporation into ethanol-soluble organic matter in the case of yellow light cultivated apices. After a 30 s pulse ¹⁴C was mainly fixed into glycerate and aspartate-malate pools whatever the pre-treatment light conditions, with a higher level into glycerate when apices were pre-illuminated with blue or yellow light. After a 180 s pulse, ¹⁴C was mainly transferred into amino acids (glutamate and alanine) at the expense of aspartate and malate in red and yellow pre-illumination conditions, as found in the white light reference experiment, and only at the expense of glycerate in blue light pre-illumination conditions.The metabolic pathway of glycerate formation, principally enhanced by blue light preillumination, remains unexplained under these non-photosynthetic conditions. Results are discussed with reference to CO₂-fixation via phosphoenolpyruvate carboxykinase and light quality effects on its in vitro activity.     

Intracellular phosphorus metabolism and growth of <Emphasis Type="Italic">Microcystis aeruginosa</Emphasis> in dark/light cycles under various redox potential difference conditions

Phosphorus metabolism and growth of M. aeruginosa were studied under three different conditions of diel fluctuation in redox potential. Redox potential in the culture increased in light and decreased in dark in all treatments except one, when cysteine was added in darkness. Total phosphorus content in M. aeruginosa decreased in darkness and increased in light during exponential growth but increased continuously in the stationary phase. Conversely, polyphosphate (PolyP) accumulated in darkness but was lost in the light. Low redox potential in darkness promoted PolyP accumulation. Polyglucose and soluble orthophosphate may provide energy and phosphorus, respectively, for PolyP synthesis. PolyP was important to M. aeruginosa survival during poor growth conditions. If the redox potential difference in the dark/light cycle was large, M. aeruginosa initially grew faster, but soon lost viability.     

Inheritance of seed coat color genes in <Emphasis Type="Italic">Brassica napus</Emphasis> (L.) and tagging the genes using SRAP,SCAR and SNP molecular markers

Seed coat color inheritance in Brassica napus was studied in F₁, F₂, F₃ and backcross progenies from crosses of five black seeded varieties/lines to three pure breeding yellow seeded lines. Maternal inheritance was observed for seed coat color in B. napus, but a pollen effect was also found when yellow seeded lines were used as the female parent. Seed coat color segregated from black to dark brown, light brown, dark yellow, light yellow, and yellow. Seed coat color was found to be controlled by three genes, the first two genes were responsible for black/brown seed coat color and the third gene was responsible for dark/light yellow seed coat color in B. napus. All three seed coat color alleles were dominant over yellow color alleles at all three loci. Sequence related amplified polymorphism (SRAP) was used for the development of molecular markers co-segregating with the seed coat color genes. A SRAP marker (SA12BG18388) tightly linked to one of the black/brown seed coat color genes was identified in the F₂ and backcross populations. This marker was found to be anchored on linkage group A9/N9 of the A-genome of B. napus. This SRAP marker was converted into sequence-characterized amplification region (SCAR) markers using chromosome-walking technology. A second SRAP marker (SA7BG29245), very close to another black/brown seed coat color gene, was identified from a high density genetic map developed in our laboratory using primer walking from an anchoring marker. The marker was located on linkage group C3/N13 of the C-genome of B. napus. This marker also co-segregated with the black/brown seed coat color gene in B. rapa. Based on the sequence information of the flanking sequences, 24 single nucleotide polymorphisms (SNPs) were identified between the yellow seeded and black/brown seeded lines. SNP detection and genotyping clearly differentiated the black/brown seeded plants from dark/light/yellow-seeded plants and also differentiated between homozygous (Y2Y2) and heterozygous (Y2y2) black/brown seeded plants. A total of 768 SRAP primer pair combinations were screened in dark/light yellow seed coat color plants and a close marker (DC1GA27197) linked to the dark/light yellow seed coat color gene was developed. These three markers linked to the three different yellow seed coat color genes in B. napus can be used to screen for yellow seeded lines in canola/rapeseed breeding programs.     

Glycogen content and nitrogenase activity in Anabaena variabilis

Nitrogenase (=acetylene-reducing activity) was followed during photoautotrophic growth of Anabaena variabilis (ATCC 29413). When cell density increased during growth, (1) inhibition of light-dependent activity by DCMU, an inhibitor of photosynthesis, increased, and (2) nitrogenase activity in the dark decreased. Addition of fructose stabilized dark activity and alleviated the DCMU effect in cultures of high cell density.The resistance of nitrogenase towards oxygen inactivation decreased after transfer of autotrophically grown cells into the dark at subsequent stages of increasing culture density. The inactivation was prevented by addition of fructose. Recovery of acetylene-reducing activity in the light, and in the dark with fructose present, was suppressed by ammonia or chloramphenicol. In the light, also DCMU abolished recovery.To prove whether the observed effects were related to a lack of photosynthetic storage products, glycogen of filaments was extracted and assayed enzymatically. The glycogen content of cells was highest 10 h after inoculation, while light-dependent nitrogenase activity was at its maximum about 24 h after inoculation. Glycogen decreased markedly as growth proceeded and dropped sharply when the cells were transferred to darkness. Thus, when C-supply (by photosynthesis or added fructose) was not effective, the glycogen content of filaments determined the activity of nitrogenase and its stability against oxygen. In cells lacking glycogen, nitrogenase activity recovered only when carbohydrates were supplied by exogenously added fructose or by photosynthesis.Abbreviations Chl chlorophyll a - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea     

Trophic dependencies of some larval chironomidae (Diptera) and fish species in the River Thames

Experiments are described to characterise the heterotrophic potential of Westiellopsis prolifica Janet, which fixes nitrogen under light and dark conditions. The growth of the organism in terms of dry weight increase, was more in fructose, lactose, sucrose, sorbose, galactose, glucose, sodium acetate, mannitol, sorbitol, glycerol, ethyl alcohol and butyl alcohol, when the alga was pretreated with light and subsequently incubated with the substrates in light. Mannose, xylose, acetic acid, propionic acid, fructose 1,6 di Po₄, pyruvic acid, dihydroxyacetone and succinic acid decreased the growth of the organism in the same condition. In dark incubation after pretreatment with light, as well as in the dark, Westiellopsis showed a better growth response to almost all the exogenous substrates. However, after pretreatment either with light or dark, the test organism utilised exogenous substrates quicker in light than in dark incubations. These experiments would suggest that the substrate specificity and efficiency of substrate utilisation by the alga during its heterotrophic growth are governed by the growth conditions.     

Effect of light and temperature on the bleaching of the yellow mutant y-1 ofEuglena gracilis

Summary The yellow mutant y-1 ofEuglena gracilis, whose plastids are chlorophyll-deficient, is stable only in the dark and at suboptimal growth temperatures (below 26 C).At growth temperature of 30 C (in darkness) this strain is unstable and undergoes permanent bleaching. The process is enhanced by light so that bleaching may be increased up to 100 per cent. The degree of bleaching is proportional to light intensity.Bleaching is possible only during the active cell division. In the resting medium there is no bleaching, but total carotenoid synthesis is stimulated by illumination. At suboptimal growth temperature (26 C) the mutant is bleached only in the light, if light intensity exceeds 2,000 Lux. The results indicate that the process of bleaching in the yellow mutant is much more sensitive to temperature and light than in wild typeEuglena.     

Influence of light on ochratoxin biosynthesis by <Emphasis Type="Italic">Penicillium</Emphasis>

Light has a profound influence on ochratoxin biosynthesis by Penicillia. When incubated under constant daylight of a certain intensity, ochratoxin A biosynthesis is decreased by about 20–30% compared to incubation under constant darkness. Under day/night oscillation, the ochratoxin A polyketide synthase gene, a key gene of the ochratoxin A biosynthesis pathway, is rhythmically expressed, and moreover, the amount of ochratoxin also oscillates between the amounts produced either during constant darkness or during constant light. This indicates a partial degradation of ochratoxin A (20–30%) under light conditions until a certain lower limit is reached. This behavior is dependent on the light intensity. At 1,600 Lux, only weak effects could be observed; however, at 2,800 Lux, the effects became significant. After growth under constant light conditions, Penicillium produced ochratoxin B at amounts which are 5 times higher than after growth in constant dark or in alternating light/dark conditions. Growth experiments in the dark on medium with increasing amounts of ochratoxin A revealed that externally applied ochratoxin is moderately toxic. However, if the same growth experiments are carried out under light conditions, the growth inhibiting activity of ochratoxin A is greatly increased, indicating that light amplifies the toxic activity of ochratoxin. Because of the oscillation of the concentration of ochratoxin A during night and day incubation, Penicillium seems to have developed an adaptive mechanism to reduce the amount of ochratoxin A during daylight below a toxic level.     

A screening model to predict microalgae biomass growth in photobioreactors and raceway ponds

A microalgae biomass growth model was developed for screening novel strains for their potential to exhibit high biomass productivities under nutrient‐replete conditions in photobioreactors or outdoor ponds. Growth is modeled by first estimating the light attenuation by biomass according to Beer‐Lambert's Law, and then calculating the specific growth rate in discretized culture volume slices that receive declining light intensities due to attenuation. The model uses only two physical and two species‐specific biological input parameters, all of which are relatively easy to determine: incident light intensity, culture depth, as well as the biomass light absorption coefficient and the specific growth rate as a function of light intensity. Roux bottle culture experiments were performed with Nannochloropsis salina at constant temperature (23°C) at six different incident light intensities (10, 25, 50, 100, 250, and 850 µmol/m² s) to determine both the specific growth rate under non‐shading conditions and the biomass light absorption coefficient as a function of light intensity. The model was successful in predicting the biomass growth rate in these Roux bottle batch cultures during the light‐limited linear phase at different incident light intensities. Model predictions were moderately sensitive to minor variations in the values of input parameters. The model was also successful in predicting the growth performance of Chlorella sp. cultured in LED‐lighted 800 L raceway ponds operated in batch mode at constant temperature (30°C) and constant light intensity (1,650 µmol/m² s). Measurements of oxygen concentrations as a function of time demonstrated that following exposure to darkness, it takes at least 5 s for cells to initiate dark respiration. As a result, biomass loss due to dark respiration in the aphotic zone of a culture is unlikely to occur in highly mixed small‐scale photobioreactors where cells move rapidly in and out of the light. By contrast, as supported also by the growth model, biomass loss due to dark respiration occurs in the dark zones of the relatively less well‐mixed pond cultures. In addition to screening novel microalgae strains for high biomass productivities, the model can also be used for optimizing the pond design and operation. Additional research is needed to validate the biomass growth model for other microalgae species and for the more realistic case of fluctuating temperatures and light intensities observed in outdoor pond cultures. Biotechnol. Bioeng. 2013; 110: 1583–1594. © 2012 Wiley Periodicals, Inc.     

Nitrogen limitation and recovery in the cyanobacterium Aphanocapsa 6308

The effects of nitrogen limitation and recovery on nitrogen-containing macromolecules were followed in the cyanobacterium Aphanocapsa 6308. Removal of nitrogen from growth media triggers the degradation of the endogenous nitrogen reserves phycocyanin and cyanophycin granule polypeptide in the cyanobacterium Aphanocapsa 6308. Nitrogen recovery involves immediate synthesis of cyanophycin granule polypeptide with peak levels of 5–12% of cell dry weight found 8–12 h after a utilizable nitrogen source is added. A rapid decrease in cyanophycin granule polypeptide level then occurs and the level remains low even in light-limited stationary growth with all nitrogen sources tested except nitrate and ammonia. Protein and phycocyanin recoveries began 3 h after a utilizable nitrogen source was added. Data suggest continuous activity of the enzyme system synthesizing cyanophycin granule polypeptide in nitrogen-limited cells, but synthesis of a degrading system only after nitrogen recovery begins.Nonstandard Abbreviations CGP Cyanophycin granule polypeptide - CAP chloramphenicol - PC phycocyanin To whom offprint requests should be sent     

Dependence of Root Growth on Photosynthesis in Populus tremula

Hoot elongation of rooted cuttings of aspen, Populus tremula L., was followed on moist filter paper. The time course of root growth during treatments which decrease or interrupt the supply of carbohydrates to the roots was studied. At light intensities below 4000 lux the rate of root elongation was found to berelated to the light intensity over the leaves. In the dark, root growth decreased within 24 hours and the roots stopped growing completely during the second or third day. Excision of the leaves or steam-killing of the tissue in a stem section below the leaves was followed by root growth stoppage within 24 hours. These results imply that the rate of root growth under certain conditions is determined by the supply of carbohydrates from the leaves.     

The effect of light on growth and sporulation of certain fungi

Summary The response of the fungi investigated to duration of exposure to light varies with the variation in the light intensity employed. Using relatively low intensity light (160 and/or 300 foot candles/inch²), the growth ofMyrothecium verrucaria &Pestalotia gracilis was not affected by the increase in the time of light exposure, while that ofPleurotus ostreatus was checked. Fruiting under the same conditions was hastened on exposure to light. Under higher light intensity (950 foot candles/inch²), growth ofMyrothecium was not affected, while that ofPestalotia andPleurotus decreased as the daily period of exposure to light increased. Pleurotus cultures exposed continuously to light showed practically no growth, and combined addition of malt and yeast extracts had a noticeable growth promoting effect on cultures exposed continuously to light, but not significantly on those kept in the dark. This was explained by assuming the presence in malt and yeast extracts of light sensitive growth promoting substances. The effect of light on growth ofPleurotus was found to be concerned with both cell mechanism and medium: light probably inhibits inside the cell the synthesis of one or more substances essential for growth and at the same time it favors the breakdown in the medium of one or more substances required for growth.