A Dynamic Metabolomic Study of Lipid Production in Chlorella Protothecoides

De nombreuses espèces d'algues se sont révélées se développer rapidement et produire des quantités substantielles de lipides. Ainsi, identifiées comme des algues oléagineuses, on a longtemps proposé que les algues pourraient être utilisées comme une usine cellulaire de production de lipides pour l’industrie des biodiesels. Cependant, la faible production de lipides, due à un métabolisme des lipides fortement interconnecté, ainsi qu’un rendement relativement faible des procédés d'extraction ont représenté des obstacles majeurs à l’industrialisation des technologies de production de lipides d'algues. Algues d'eau douce Chlorella protothecoides était l'espèce la plus métabolique diverse et robuste trouvée dans les littératures. Il pourrait appliquer trois modes de culture différents, qui sont autotrophes sur le CO2, l'alimentation mixotrophique sur le CO2 et le glucose, et l'hétérotrophie avec le glucose uniquement. Dans cette espèce, la teneur en lipides et le rendement en biomasse étaient beaucoup plus élevés en mode de culture hétérotrophique par rapport au mode de culture autotrophique. Bien que les recherches montrent que le glucose pourrait inhiber l'affinité du CO2 dans le système de fixation du CO2 et avoir un fort effet inhibiteur sur les enzymes du cycle de Calvin ainsi que sur les protéines de collecte de lumière, l'impact de la régulation du glucose sur le niveau métabolique n'était pas clair. L'objectif principal du travail était d'améliorer le rendement lipidique des algues, en mettant l'accent sur l'ingénierie métabolique basée sur l'étude métabolomique et une modélisation cinétique, ainsi que sur l'exploration de nouvelles approches et de méthodes efficaces d'extraction des lipides, afin d'améliorer la cellule d'algues comme plate-forme d'accumulation de lipides pour la production de biodiesel. Dans la première partie, nous avons étudié différents modes de culture à base de carbone, tels que autotrophes, mixotrophes et hétérotrophes sous un faible pouvoir azoté. Sous un faible taux d'azote, les lipides pourraient être évidemment accumulés; Pendant ce temps, la différence de métabolisme cellulaire pourrait être clairement observée à cause de l'impact du glucose. L'objectif était de démêler les liens et la régulation entre le métabolisme du carbone des algues et la production de lipides. Dans cet article, nous nous concentrons profondément sur l'étude du métabolisme et de la régulation de la production de lipides dans la plate-forme d'algues et apporte une nouvelle connaissance de la régulation dans le métabolisme des lipides d'algues. Surtout, c'est la première fois que l'on étudie la dynamique de l'énergie dans les algues et que l'on retrouve la capacité de vii rotation de l'énergie dans les modes de culture hétérotrophes et mixotrophes pour une forte accumulation de lipides. La deuxième partie de ce travail a porté sur le développement d'un modèle métabolique cinétique décrivant le métabolisme central du carbone de Chlorella protothecoides cultivé dans des conditions hétérotrophes. Le modèle comprend la plupart des principales voies du métabolisme cellulaire. On a montré que les simulations de modèles concordaient avec les données expérimentales, ce qui suggère que la structure de modèle proposée fait face à la biologie des cellules de Chlorella protothecoides. Le modèle a permis d'effectuer une analyse dynamique du flux métabolique et nous a permis de démontrer que le rendement lipidique élevé s'accompagne d'un flux lipidique élevé et d'une faible activité TCA. Pendant ce temps, la distribution du flux dynamique suggère également un métabolisme stable et robuste dans Chlorella protothecoides avec un rapport relativement constant de la distribution du glucose. Ce modèle est un premier modèle métabolique cinétique dans les plates-formes d'algues et a jeté une base de base pour servir d'outil pour prédire l'ingénierie génétique ainsi que la stratégie de culture de conception pour une production optimisée de lipides en la définissant comme fonction objective. Dans la troisième et dernière partie, nous avons travaillé à améliorer les protocoles d'extraction des lipides actuels, afin de maximiser le rendement de l'extraction des lipides. Une étape de traitement de l'eau a été ajoutée et adaptée aux protocoles d'extraction actuels, entre les deux extractions de solvant organique. Les résultats ont montré que le traitement de l'eau de la biomasse après la première étape d'extraction du solvant aide à la libération des lipides intracellulaires dans la deuxième étape d'extraction, améliorant ainsi le rendement final d'extraction des lipides. Le nouveau procédé fournit donc un moyen efficace d'améliorer le rendement en extraction des lipides des méthodes existantes, ainsi que de favoriser le TAG, un lipide présentant le plus grand intérêt pour la production de biodiesel. En résumé, ce travail a permis de décrire le comportement métabolique de la production de lipides chez Chlorella protothecoides. La combinaison d'un outil d'ingénierie métabolique en amont et d'une approche optimisée de l'extraction des lipides en aval a clairement contribué à améliorer la faisabilité commerciale du bioprocessage de la production de lipides à base de microalgues. ----------- Many algal species have been found to grow rapidly and produce substantial amounts of lipid. These microalgae are identified as oleaginous algae and it has long been proposed that algae could be employed as a cell factory to produce lipids for biodiesel. However, low lipid production level, because of a highly regulated lipid metabolism as well as relatively low lipid extraction yields, have been major barriers to the practical application of algae lipid technologies industrially. Fresh water algae Chlorella protothecoides was the most metabolic diverse and robust species found in literatures. It could apply three different culture modes, which are autotrophic on CO2, mixotrophic feeding on CO2 and glucose, and heterotrophic with glucose only. In this species, lipid content and biomass yield were much higher under heterotrophic culture mode compared with autotrophic culture mode. Although researches found glucose could inhibit the affinity of CO2 in the CO2 fixation system, and have strong inhibitory effect on Calvin cycle enzymes as well as on light gathering proteins, the impact of glucose regulation on metabolic level were not clear. The main objective of this thesis was thus to improve the algae lipid yield, with a special emphasis on a metabolic engineering approach based on a metabolomics study, kinetic modeling as well as on exploring new approaches of efficient lipid extraction methods, in order to improve algae cell as a lipid accumulation platform for biodiesel production. In the first part, we studied different carbon-based culture modes, such as autotrophic, mixotrophic, and heterotrophic under a low nitrogen medium condition. Under low nitrogen condition, lipid could be obviously accumulated; meanwhile the difference of cell metabolism could be clearly seen from glucose impact. The aim was to unravel the links and regulation between algae carbon metabolism and lipid production. In this article, we deeply focus on the metabolism and regulation study of lipid production in algae platform and it brings novel knowledge of regulation in algae lipid metabolism. Especially it’s the first time to investigate the energy dynamic in algae and found energy turn over capacity in heterotrophic and mixotrophic culture modes for high lipid accumulation. The second part of this work focused on the development of a kinetic metabolic model describing Chlorella protothecoides central carbon metabolism grown under heterotrophic condition. The model includes most of the major pathways of the cell metabolism. Model simulations were shown to agree with experimental data, which is suggesting that the proposed model structure copes with ix Chlorella protothecoides cells’ biology. The model enabled performing a dynamic metabolic flux analysis, and enabled us to demonstrate that high lipid yield is accompanied with high lipid flux and low TCA activity. Meanwhile, the dynamic flux distribution also suggests a robust and stable metabolism in Chlorella protothecoides with relatively constant ratio of glucose distribution. This model is a first kinetic metabolic model in algae platforms and laid a basic foundation to serve as a tool in predicting genetic engineering as well as design culture strategy for optimized lipid production by defining it as objective function. In the third and final part, we worked at improving current lipid extraction protocols, to maximize lipid extraction yield. A water treatment step was added and adapted to current extraction protocols, between the two organic solvent extractions. Results showed water treatment of biomass after the first solvent extraction step helps the release of intracellular lipids in the second extraction step, thus improving the final lipids extraction yield. The novel method thus provides an efficient way to improve lipid extraction yield of existing methods, as well as favoring TAG, a lipid of the highest interest for biodiesel production. In conclusion, this thesis allowed ameliorating our understanding of the links between cell metabolomic behavior and lipid production in Chlorella protothecoides. The combination of an upstream metabolic engineering tool and an optimized downstream lipid extraction approach has clearly contributed to ameliorate the commercial feasibility of lipids production bioprocess based on microalgae

A Search for Spectral Galaxy Pairs of Overlapping Galaxies based on Fuzzy Recognition

The Spectral Galaxy Pairs (SGPs) are defined as the composite galaxy spectra which contain two independent redshift systems. These spectra are useful for studying dust properties of the foreground galaxies. In this paper, a total of 165 spectra of SGPs are mined out from Sloan Digital Sky Survey (SDSS) Data Release 9 (DR9) using the concept of membership degree from the fuzzy set theory particularly defined to be suitable for fuzzily identifying emission lines. The spectra and images of this sample are classified according to the membership degree and their image features, respectively. Many of these 2nd redshift systems are too small or too dim to select from the SDSS images alone, making the sample a potentially unique source of information on dust effects in low-luminosity or low-surface-brightness galaxies that are underrepresented in morphological pair samples. The dust extinction of the objects with high membership degree is also estimated by Balmer decrement. Additionally, analyses for a series of spectroscopic observations of one SGP from 165 systems indicate that a newly star-forming region of our Milky Way might occur.Comment: 16pages, 6figure

Coupling between phase transitions and glassy magnetic behaviour in Heusler alloy Ni 50 Mn 34 In 8 Ga 8

Abstract: The transition sequence in the Heusler alloy Ni50Mn34In8Ga8 has been determined from measurements of elasticity, heat flow and magnetism to be paramagnetic austenite → paramagnetic martensite → ferromagnetic martensite at ∼335 and ∼260 K, respectively, during cooling. The overall pattern of elastic stiffening/softening and acoustic loss is typical of a system with bilinear coupling between symmetry breaking strain and the driving structural/electronic order parameter, and a temperature interval below the transition point in which ferroelastic twin walls remain mobile under the influence of external stress. Divergence between zero-field-cooling and field-cooling determinations of DC magnetisation below ∼220 K indicates that a frustrated magnetic glass develops in the ferromagnetic martensite. An AC magnetic anomaly which shows Vogel–Fulcher dynamics in the vicinity of ∼160 K is evidence of a further glassy freezing process. This coincides with an acoustic loss peak and slight elastic stiffening that is typical of the outcome of freezing of ferroelastic twin walls. The results suggest that local strain variations associated with the ferroelastic twin walls couple with local moments to induce glassy magnetic behaviour

Coupling between phase transitions and glassy magnetic behaviour in Heusler Alloy Ni50Mn34In8Ga8

The transition sequence in the Heusler alloy Ni50Mn34In8Ga8 has been determined from measurements of elasticity, heat flow and magnetism to be paramagnetic austenite → paramagnetic martensite → ferromagnetic martensite at ~335 and ~260 K, respectively, during cooling. The overall pattern of elastic stiffening/softening and acoustic loss is typical of a system with bilinear coupling between symmetry breaking strain and the driving order parameter in a temperature interval below the transition point in which ferroelastic twin walls remain mobile under the influence of external stress. Divergence between zero-field-cooling (ZFC) and field-cooling (FC) determinations of DC magnetisation below ~220 K indicates that a frustrated magnetic glass develops in the ferromagnetic martensite. An AC magnetic anomaly which shows Vogel-Fulcher dynamics in the vicinity of ~160 K is evidence of a further glassy freezing process. This coincides with an acoustic loss peak and slight elastic stiffening that is typical of the outcome of freezing of ferroelastic twin walls. The results indicate that local strain variations associated with the ferroelastic twin walls couple with local moments to induce glassy magnetic behaviour

Optical phonons, OH vibrations, and structural modifications of phlogopite at high temperatures: An in-situ infrared spectroscopic study

The thermal behavior of optical phonons and OH vibrations of phlogopite (a trioctahedral mica) was examined at temperatures up to 1000 K using in situ infrared spectroscopy. The results showed that with increasing temperature, O–K bands in phlogopite exhibited a relatively strong variation in frequency in a manner similar to those in muscovite. The work revealed that different types of OH bands (fundamentals and combinations) have very different thermal behavior or temperature dependence, and their absorption coefficients are commonly not constant on heating. OH combination bands that are associated with summation processes of multi-phonon interactions commonly show a decrease in their intensities on heating, but in contrast combination bands due to difference processes generally exhibit an increase. This means that temperature dependencies of their absorption coefficients need to be considered when using the Beer-Lambert law to determine or estimate OH contents or hydrogen concentrations at high temperatures. The results showed a structural anomaly associated with a discontinuity in the temperature derivative of the wavenumber of Al–O and Si–O vibrations and O–H stretching near 600 K. However, framework-related phonon modes in the FIR and MIR regions do not suggest a break of the original monoclinic structural symmetry in the investigated temperature region. The complex changes are attributed to temperature-induced alteration of local configuration involving TO4 tetrahedra and a possible change of the orientation of OH dipoles, in addition to a previously reported distortion of MO6 octahedra. Increasing temperature to 1000 K also causes partial dehydroxylation, as evidenced by the disappearance of the OH band near 3623 cm−1 and the decrease in OH band height and area of other OH bands. The study did not record the formation of H2O inside phlogopite as a result of partial dehydroxylation. The work offers new data and findings that have important implications in understanding the complex structural modifications and the behavior of phonon modes and the thermal stability of hydroxyls on approaching the dehydroxylation, as well as the way hydrogen is released from micas at high temperatures. Our data also show that phologpite becomes less transparent with increasing temperature suggesting a change of radiative properties and ability to transmit heat, which could be of interest for modeling thermal-transmission in crustal rocks

Screening for Climate Change Adaptation: Managing the Potential Impacts of Climate Change on Water Sector in China

The issue on screening for climate change adaptation is addressed. A screening approach is developed for assessing climatechange impacts on water sector and integrating adaptation for water resource projects, and three phases for screening climate changeadaptation are introduced that include the semi-quantitative & quantitative analysis, and the evaluation of different adaptation optionson the water resources affected by climate change in China. According to different climatic regions facing different problems on waterresource, four representative regions in China are chosen in the project; after setting up different objectives, this paper demonstrates thecomprehensive research on climate change adaptation, and proposes new ideas, framework and methodologies on screening for climatechange impacts and adaptation. This research provides the effective framework and methodology for the planning and risk managementof the impacts of future climate change on water resource

气候变化对中国水资源影响的适应性评估 与管理框架

摘 要：通过论述气候变化对中国水资源影响的适应性评估与管理框架，提出一个气候变化影响决策评估工具，它包括： 未来气候变化对中国水资源潜在影响的定性描述分析、半定量与定量分析以及适应性对策评估。由于不同气候区域所面 临的水资源问题不同，选择中国4 个典型案例区域，并确定不同的目标进行气候变化适应性管理综合研究，提出了甄别 气候变化影响和适应性管理的新的思路、框架与方法论。该项研究为应对未来气候变化影响的水资源规划与风险管理提 供了途径与方法。 关键词：气候变化；水资源；适应性管

Social dilemmas in an online social network: the structure and evolution of cooperation

We investigate two paradigms for studying the evolution of cooperation--Prisoner's Dilemma and Snowdrift game in an online friendship network obtained from a social networking site. We demonstrate that such social network has small-world property and degree distribution has a power-law tail. Besides, it has hierarchical organizations and exhibits disassortative mixing pattern. We study the evolutionary version of the two types of games on it. It is found that enhancement and sustainment of cooperative behaviors are attributable to the underlying network topological organization. It is also shown that cooperators can survive when confronted with the invasion of defectors throughout the entire ranges of parameters of both games. The evolution of cooperation on empirical networks is influenced by various network effects in a combined manner, compared with that on model networks. Our results can help understand the cooperative behaviors in human groups and society.Comment: 14 pages, 7 figure