Improvement of Neutral Lipid and Polyunsaturated Fatty Acid Biosynthesis by Overexpressing a Type 2 Diacylglycerol Acyltransferase in Marine Diatom Phaeodactylum tricornutum

Microalgae have been emerging as an important source for the production of bioactive compounds. Marine diatoms can store high amounts of lipid and grow quite quickly. However, the genetic and biochemical characteristics of fatty acid biosynthesis in diatoms remain unclear. Glycerophospholipids are integral as structural and functional components of cellular membranes, as well as precursors of various lipid mediators. In addition, diacylglycerol acyltransferase (DGAT) is a key enzyme that catalyzes the last step of triacylglyceride (TAG) biosynthesis. However, a comprehensive sequence-structure and functional analysis of DGAT in diatoms is lacking. In this study, an isoform of diacylglycerol acyltransferase type 2 of the marine diatom Phaeodactylum tricornutum was characterized. Surprisingly, DGAT2 overexpression in P. tricornutum stimulated more oil bodies, and the neutral lipid content increased by 35%. The fatty acid composition showed a significant increase in the proportion of polyunsaturated fatty acids; in particular, EPA was increased by 76.2%. Moreover, the growth rate of transgenic microalgae remained similar, thereby maintaining a high biomass. Our results suggest that increased DGAT2 expression could alter fatty acid profile in the diatom, and the results thus represent a valuable strategy for polyunsaturated fatty acid production by genetic manipulation.     

Using micro particle diets to replace diatoms for feeding postlarval abalone Haliotis discus discus (Reeve.)

Feeding artificial micro diets instead of diatoms may allow a more constant and controlled form of nutrition, and thus results in lower mortality rate and increased growth. A 4-week trial was conducted to determine the growth and survival of postlarval Haliotis discus discus (Reeve.) postlarvae fed three experimental micro particle diets, and naturally occurring diatoms. A completely randomized design was adopted with each diet being replicated three times. All diets varied in terms of particle size and gross composition. Survival rate was significantly lower ( P  < 0.05) in the diatom diet (19.5 ± 2.1%) when compared with the K-1 diet (38.8 ± 8.9%), the K-2 diet (43.7 ± 5.6%) and the MD-Q diet (44.2 ± 14.8%). The size of postlarvae fed the four diets was not significantly different ( P  > 0.05). There was also little difference in the daily growth rate. Based on the results of this work for the preliminary implementation of artificial food as a replacement diet for diatoms, it seems that postlarval H . discus discus readily consumes artificial micro particle diets and has a superior survival rate when compared to that of diatoms.     

基于海洋硅藻的生物燃油生产

微藻与陆生作物相比,具有生物量大、生长周期短、脂质含量高、不占用耕地等特点,已成为生物燃油原料的首选。微藻生物燃油的经济性生产,需要建立能保持单一藻种优势的开放型微藻生产系统。采用海洋硅藻——角毛藻(Chaetoceros)作为讨论对象,综述了目前基于海洋硅藻的生物燃油生产系统设计所应用的技术:在开放型系统中生产硅藻,从生长介质中收获硅藻,从收获的硅藻中提取油脂和脂肪酸,以及整体的经济性。     

3种淡水硅藻油脂的含量与成分分析

为探索3种淡水硅藻(小头端菱形藻、尖针杆藻、肘状针杆藻丹麦变种)作为生物柴油原料的潜能,培养并检测了其油脂含量及成分.结果表明:小头端菱形藻生长周期最短,生物量最高.3种淡水硅藻中总脂含量为2.92%～9.2500,小头端菱形藻的总脂含量最高,达9.25 %;脂肪酸的组成相似,且3种硅藻主要脂肪酸成分是豆蔻酸(C14:0)、软脂酸(C16:0)、棕榈油酸(C16:1)、油酸(C18:1)、亚油酸(C18:2)和十八碳四烯酸(C18:4).不饱和脂肪酸含量均占总脂肪酸含量的60%以上,小头端菱形藻达63.54%.进一步改善培养条件后小头端菱形藻可作为生产生物柴油的原料.     

武汉月湖沉积物中硅藻的垂直分布与水质变化

采用活塞取样器采集了月湖湖中央2处钻孔沉积物,分析了其中硅藻种类与密度的垂直变化,同时采用210Pb/137Cs推测沉积物的沉积速率.并进行了总有机质、生物硅含量分析,以了解月湖各个不同年代的水质变化.结果表明,2个柱状沉积物中硅藻的优势属为:小环藻属、直链藻属、舟形藻属、Cyclostephanos属.Z-1钻孔优势种为:梅尼小环藻、颗粒直链藻、Navicula porifera、Cyclostephanos tholifomis.Z-2钻孔中优势种为:梅尼小环藻、颗粒直链藻、舟形藻、Cyclostephanos invisitatus.就硅藻密度而言,总趋势是上层最多,平均7.14×105～58.65×105 ind·g-1,中层其次,平均0.08×105～13.98×105 ind·g-1,下层最少,平均0.24×105～0.64×105 ind·g-1.硅藻种类数变化虽然没有明显规律,但种类最少的样品出现在中层,210Pb/137Cs测年数据表明中层为19世纪90年代-20世纪70年代.相关分析表明:Z-1孔生物硅与沉积硅藻密度显著正相关(r=0.933,P=0.021<0.05),总有机质含量与种类数显著负相关(r=-0.972,P=-0.005<0.05);Z-2孔生物硅与沉积硅藻密度显著正相关(r=0.985,P=0.002<0.05),沉积硅藻密度与种类数显著负相关(r=-0.933,P=0.021<0.05).研究结果表明,月湖沉积物中硅藻种类与密度的垂直变化可以反映月湖的富营养演化历程:19世纪60年代-19世纪80年代,月湖水质较好;19世纪90年代-20世纪10年代,月湖开始由贫营养状态向中营养状态转变,为水体富营养化开始发生时间;20世纪20年代-20世纪40年代,月湖水体营养等级持续增加,已富营养化;20世纪50年代-20世纪70年代,周边人口数量急剧上升与污水的直接排放导致月湖水质持续恶化;20世纪80年代至月湖截污前这段时期使月湖最终沦为劣五类水体的湖泊.     

Effect of an Introduced Phytoene Synthase Gene Expression on Carotenoid Biosynthesis in the Marine Diatom Phaeodactylum tricornutum

Carotenoids exert beneficial effects on human health through their excellent antioxidant activity. To increase carotenoid productivity in the marine Pennales Phaeodactylum tricornutum, we genetically engineered the phytoene synthase gene (psy) to improve expression because RNA-sequencing analysis has suggested that the expression level of psy is lower than other enzyme-encoding genes that are involved in the carotenoid biosynthetic pathway. We isolated psy from P. tricornutum, and this gene was fused with the enhanced green fluorescent protein gene to detect psy expression. After transformation using the microparticle bombardment technique, we obtained several P. tricornutum transformants and confirmed psy expression in their plastids. We investigated the amounts of PSY mRNA and carotenoids, such as fucoxanthin and β-carotene, at different growth phases. The introduction of psy increased the fucoxanthin content of a transformants by approximately 1.45-fold relative to the levels in the wild-type diatom. However, some transformants failed to show a significant increase in the carotenoid content relative to that of the wild-type diatom. We also found that the amount of PSY mRNA at log phase might contribute to the increase in carotenoids in the transformants at stationary phase.     

底栖硅藻种类和密度对仿刺参幼体和稚参生长与成活的影响

在水温为22.0~26.0℃下,研究了不同密度的圆筛藻Coscinodiscus sp.、舟形藻Navicula sp.和双肋藻Amphipteura sp.及其等比例组合对仿刺参Apostichopus japonicus体长为400~500μm的樽形幼体变态、附着及生长和成活的影响。结果表明：在单一硅藻组中,圆筛藻组幼体的附着率最高（13.3%±2.2%）,显著高于舟形藻（6.9%±1.8%）和双肋藻组（5.9%±0.7%）（P〈0.05）;混合硅藻组的附着率均高于单一硅藻组,其中圆筛藻＋舟形藻组幼体的附着率（23.2%±3.2%）显著高于对照组（18.0%±2.16%）（P〈0.05）。混合藻类密度为1~25万个/cm2时,幼体的附着率（27.2%±4.28%）均显著高于对照组（P〈0.05）。经过46 d的饲养,单一和混合藻类组幼参的最终体长（P〈0.01）和成活率（P〈0.05）均显著低于对照组。稚参变态附着后至体长为700~800μm的10 d内,以3种混合底栖硅藻为食物,之后以营养来源丰富的人工饵料为食,可明显提高仿刺参的生长速度和育苗成活率。     

Changes in Lipid and Fatty Acid Compositions of European Oysters Fattened with Skeletonema Costatum Diatom for Six Weeks in Ponds

To improve the condition index of European oysters (Crassostrea gigas), Skeletonema costatum was fed to adult oysters. However, the consequences of this practice on compositional traits of oysters were not investigated. This study deals with the chemical changes in oysters fed with Skeletonema costatum for six weeks in ponds.The results showed that:1. Supplying Skeletonema costatum to oysters for six weeks improved the condition index (from 26 to 56) as a consequence of an increase in glycogen content (from 5.0 to 24.4 g·100 g ^–1 of dry flesh) while lipid content remained steady (9.9 g·100 g^–1 dry flesh).2. Large changes in fatty acid composition of neutral lipids were observed. Some fatty acids of Skeletonema costatum such as 16:1 7 and 20:5 3, were directly accumulated into lipid fractions.3. 16:1 7 was elongated into 18:1 7 showing that oysters are able to elongate 16 carbon mono-unsaturated fatty acids into the corresponding 18 carbon fatty acids.4. Fatty acids typical of Skeletonema costatum (16:4 1, 16:2 4, 16:3 4) were poorly accumulated into neutral lipids and phospholipids of oysters suggesting that oysters discriminate these fatty acids.     

赤水河流域秋季底栖硅藻群落结构特征及水质评价

为研究赤水河流域底栖硅藻群落特征及水质状况,2019年9月测定了赤水河流域36个代表性样点的水体理化指标,调查了底栖硅藻群落组成,并应用硅藻指数评价了赤水河流域的水质状况。结果表明：秋季赤水河流域上游的电导率和总磷、总氮浓度均高于下游;调查采集到底栖硅藻29属138种,其中扁圆卵形藻多孔变种(Cocconeis placentula var. euglypta)、变异直链藻（Melosira varians）、极细微曲壳藻（Achnanthes minutissima）和谷皮菱形藻（Nitzschia palea）等为秋季赤水河流域优势种;下游底栖硅藻群落稳定性高于中上游;CCA结果显示可溶活性磷（SRP）和总氮（TN）是影响赤水河流域底栖硅藻群落的主要环境因子。TDI和CEE硅藻指数评价结果表明,赤水河流域水质等级整体为“中等”,55.6%的样点水质等级为“中等”以上,8.3%的样点水质等级为“极差”。     

Biochemical and Genetic Engineering of Diatoms for Polyunsaturated Fatty Acid Biosynthesis

The role of diatoms as a source of bioactive compounds has been recently explored. Diatom cells store a high amount of fatty acids, especially certain polyunsaturated fatty acids (PUFAs). However, many aspects of diatom metabolism and the production of PUFAs remain unclear. This review describes a number of technical strategies, such as modulation of environmental factors (temperature, light, chemical composition of culture medium) and culture methods, to influence the content of PUFAs in diatoms. Genetic engineering, a newly emerging field, also plays an important role in controlling the synthesis of fatty acids in marine microalgae. Several key points in the biosynthetic pathway of PUFAs in diatoms as well as recent progresses are also a critical part and are summarized here.