Hydrogen production from biological systems under different illumination conditions

Hydrogen is a natural by-product of several microbial driven biochemical reactions, mainly in anaerobic fermentation processes. In addition, certain microorganisms produce enzymes by which H₂ from water may be obtained if an outside energy source, like sunlight, is provided. Biophotolysis is a biological process which involves solar energy and algae clusters to convert water into hydrogen. Algae pigments absorb solar energy and enzymes in the cell act as catalysts to split water into hydrogen and oxygen. There are many research activities studying hydrogen production from biological systems cyanobacteria and green algae and some studies present a complete outline of the main available pathways to improve the photosynthetic H₂ production [1] and [2].Efficiency (energy produced from hydrogen divided by solar energy) of such processes can be estimated up to 10%. This value has to be increased for a large-scale hydrogen production. The effect of different artificial illumination conditions on H₂ production was studied for green algae cultures (Chlamydomonas reinhardtii). Results will be used to design a high-efficiency photobioreactor for a large-scale hydrogen production.     

Effects of culture parameters, light, and mixing on H2 production by sulfur-deprived Chlamydomonas reinhardtii in flat plate reactor

Based on advective-diffusive reaction equation for inhomogeneous biochemical system and an empirical equation for light attenuation coefficient, the interplay among culture parameters, light intensity and illumination condition, and mechanical mixing condition during O₂ evolution and H₂ production in a flat plate photobioreactor with sulfur-deprived Chlamydomonas reinhardtii culture is modeled in this work. Four initial chlorophyll concentrations, two light attenuation levels, and two illumination conditions were modeled to study their effects on the dynamics of O₂ evolution and H₂ production. The results indicate that two side illumination is the best design for light penetration into a flat plate reactor. While for single side illumination condition, an optimal combination of the initial cell concentration, light intensity, and reactor width may have to be considered for high H₂ production.     

南极冰藻Chlamydomonas sp. L4的UV-B辐射效应研究

实验研究了从南极采集的冰藻Chlamydomonas sp. L4经强UV-B辐射胁迫后的生物学效应及逆境适应性.研究显示,经过强UV-B胁迫,冰藻L4细胞内迅速产生大量的活性氧,丙二醛含量升高;同时,SOD活性快速提高,使活性氧和丙二醛含量维持在细胞容许范围之内.膜脂肪酸成分分析发现不饱和指数增加了近4倍,膜流动性增加 ,从而维持膜的正常功能.光学显微镜、扫描和透射电镜观察表明,UV-B辐射使细胞体积显著增大,黏性多糖分泌增多,细胞壁增厚,未知黑色颗粒密度增加,L4可能通过上述结构变化把 UV-B屏蔽在胞外.脂肪颗粒的增加是细胞在逆境生存的能量保障.此外,细胞中类囊体片层、线粒体和细胞核等结构基本没有变化,维持细胞基本的代谢和能量供应.     

PCD Genes—From Patients to Model Organisms and Back to Humans

Primary ciliary dyskinesia (PCD) is a hereditary genetic disorder caused by the lack of motile cilia or the assembxly of dysfunctional ones. This rare human disease affects 1 out of 10,000–20,000 individuals and is caused by mutations in at least 50 genes. The past twenty years brought significant progress in the identification of PCD-causative genes and in our understanding of the connections between causative mutations and ciliary defects observed in affected individuals. These scientific advances have been achieved, among others, due to the extensive motile cilia-related research conducted using several model organisms, ranging from protists to mammals. These are unicellular organisms such as the green alga Chlamydomonas, the parasitic protist Trypanosoma, and free-living ciliates, Tetrahymena and Paramecium, the invertebrate Schmidtea, and vertebrates such as zebrafish, Xenopus, and mouse. Establishing such evolutionarily distant experimental models with different levels of cell or body complexity was possible because both basic motile cilia ultrastructure and protein composition are highly conserved throughout evolution. Here, we characterize model organisms commonly used to study PCD-related genes, highlight their pros and cons, and summarize experimental data collected using these models.     

衣藻生物吸附铜的实验研究

以莱茵衣藻为生物吸附材料,研究了其对Cu的生物吸附。结果表明:衣藻在6 h内对Cu的生物吸附达到了平衡;衣藻对Cu的生物吸附符合Freundlich等温吸附方程(y=0.3912x0.7188;R2=0.9784);衣藻对Cu的吸附能力很强,可用衣藻来处理含Cu离子的废水。     

水环境中莱茵衣藻对纳米氧化铜的吸附及离子溶出的影响

以莱茵衣藻为研究对象,采用批量试验研究了莱茵衣藻对纳米氧化铜的吸附过程及其对自由金属离子溶出的影响。试验结果表明,莱茵衣藻对纳米氧化铜具有较强的吸附能力,吸附遵循Langmuir和Freundlich等温线模型和准二次动力学模型,最大吸附量为128 μg/10⁶个藻细胞。莱茵衣藻的存在对自由金属离子溶出具有显著影响,低浓度的莱茵衣藻促进Cu²⁺溶出,高浓度的莱茵衣藻抑制Cu²⁺溶出。     

Fluorescence lifetime imaging microscopy of Chlamydomonas reinhardtii: non-photochemical quenching mutants and the effect of photosynthetic inhibitors on the slow chlorophyll fluorescence transient

Fluorescence lifetime‐resolved images of chlorophyll fluorescence were acquired at the maximum P‐level and during the slower transient (up to 250 s, including P‐S‐M‐T) in the green photosynthetic alga Chlamydomonas reinhardtii. At the P‐level, wild type and the violaxanthin‐accumulating mutant npq1 show similar fluorescence intensity and fluorescence lifetime‐resolved images. The zeaxanthin‐accumulating mutant npq2 displays reduced fluorescence intensity at the P‐level (about 25–35% less) and corresponding lifetime‐resolved frequency domain phase and modulation values compared to wild type/npq1. A two‐component analysis of possible lifetime compositions shows that the reduction of the fluorescence intensity can be interpreted as an increase in the fraction of a short lifetime component. This supports the important photoprotection function of zeaxanthin in photosynthetic samples, and is consistent with the notion of a ‘dimmer switch’. Similar, but quantitatively different, behaviour was observed in the intensity and fluorescence lifetime‐resolved imaging measurements for cells that were treated with the electron transport inhibitor 3‐(3,4‐dichlorophenyl)‐1,1‐dimethyl urea, the efficient PSI electron acceptor methyl viologen and the protonophore nigericin and. Lower fluorescence intensities and lifetimes were observed for all npq2 mutant samples at the P‐level and during the slow fluorescence transient, compared to wild type and the npq1 mutant. The fluorescence lifetime‐resolved measurements during the slow fluorescence changes after the P level up to 250 s for the wild type and the two mutants, in the presence and absence of the above inhibitors, were analyzed with a graphical procedure (polar plots) to determine lifetime compositions. At higher illumination intensity, wild type and npq1 cells show a rise in fluorescence intensity and corresponding rise in the species concentration of the slow lifetime component after the initial decrease following the P level. This reversal is absent in the npq2 mutant, and for all samples in the presence of the inhibitors. Lifetime heterogeneities were observed in experiments averaged over multiple cells as well as within single cells, and these were followed over time. Cells in the resting state (induced by several hours of darkness), instead of the normal swimming state, show shortened lifetimes. The above results are discussed in terms of a superposition of effects on electron transfer and protonation rates, on the so‐called ‘State Transitions’, and on non‐photochemical quenching. Our data indicate two major populations of chlorophyll a molecules, defined by two ‘lifetime pools’ centred on slower and faster fluorescence lifetimes.     

Photo-bioproduction of hydrogen by Chlamydomonas reinhardtii using a semi-continuous process regime

Photo-bioproduction of hydrogen by using green algae, Chlamydomonas reinhardtii, was investigated in batch and semi-continuous process regimes, in a continuous stirred type photobioreactor. Batch cultivation was carried out for 35 days which was one of the longest cited in literature. Total hydrogen production with batch culture reached 316 ml. The observations from the batch culture provided useful data about the production process. Three important observations were made from the batch cultivation. One was the requirement of a 2 day-lag time for the start of the hydrogen production. Second one was the fact that the maximum hydrogen production is reached at around day 4. Third one was the decline of hydrogen production after a week. Semi-continuous regime was preferred rather than a continuous one based on these data. Semi-continuous cultivation was continued for 127 days yielding a total hydrogen production of 1108 ml. In the semi-continuous process, the effects of parameters such as dilution ratio, dilution frequency and fresh medium addition were studied. The range of these parameters was also decided, based on the batch cultivation data. Each experiment testing for different parameters lasted for 7 days and thus five consecutive sets were completed in 35 days.The results showed a direct correlation between the amount and frequency of dilution and hydrogen production. Semi-continuous regime gave the opportunity of dividing the continuous production in consecutive batches and the process was in good relation with batch regime.