日照和蒸散发量对微藻生长的影响

【目的】微藻是可以进行光合作用的水生生物,不仅可用作为生产生物柴油的原料,同时也可用于生产高蛋白食物和动物饲料等。微藻生长不与陆生植物竞争土地资源,其整体应用对可持续农业发展的潜力巨大。高产量微藻养殖对微藻整体产业发展至关重要,以室外硅藻养殖为实例,探讨生长阶段光照和需水量等要素与产量的关系,为大规模养殖管理提供指导。【方法】利用深圳兆凯生物能源研究中心室外硅藻养殖平台,研究硅藻养殖的适宜设备和生长条件,收集开放式光反应器硅藻养殖系统生长阶段的每日产量数据;同时从深圳市气象局和深圳大学城北大气象观测站收集相应的温度、光照、湿度等气象资料。通过光合作用模型量化硅藻生长的光照需求,同时利用SIMMETEO模型结合温度、光照、湿度等气象要素模拟硅藻生长过程的日蒸散发量。最终通过统计分析建立光照、水分需求量和硅藻产量的关系模型,研究其对硅藻生长的影响。【结果】在年均温度较高的地区,相较于太阳辐射等气象因素,温度对硅藻日产量的影响相对较小,其线性拟合优度R²=0.464。太阳辐射对硅藻日产量影响显著,其线性拟合优度R2=0.656。同时,太阳辐射与蒸散发量有显著相关性,其sigmoidal曲线拟合优度达0.962。当每日太阳辐射值为9.67-12.67 MJ•m-2时,其对硅藻的蒸散发量影响最大;当每日太阳辐射值超过12.67 MJ•m-2时,硅藻的日蒸散发量不再随太阳辐射增大而增加,维持在4.63 mm左右,表明该生长系统的水分需求已达饱和。蒸散发量实际代表硅藻生长阶段的水需求量,硅藻日产量与日蒸散发量的线性拟合优度R2=0.637,表明蒸散发量对硅藻生长也有显著影响,硅藻生长需要适当的水分供给,当水分供给受限,不能满足生长需求,产量增长则受到限制;同时,硅藻生物量的增加也会导致水需求量的不断增大,以满足生理生化过程。【结论】太阳辐射和蒸散发对微藻生长有显著影响,是提高微藻产量时必须考虑的重要因素。硅藻需水量相比光照需求,更易量化和控制,研究硅藻的蒸散发量可以明确硅藻实际生长过程中的水分需求,为有效地进行水分供给提供依据,可应用为微藻养殖供水管理方面的有效工具。     

Changes in oil content,lipid class and fatty acid composition of the microalga Chaetoceros calcitrans over different phases of batch culture

The diatom Chaetoceros calcitrans is a microalgal species used as food for larva in aquaculture for many species worldwide. Chaetoceros calcitrans is an important source of omega 3 long chain (C ≥ 20) polyunsaturated fatty acids (n‐3 LC PUFA), chiefly eicosapentaenoic acid (EPA, 20:5n‐3). This article reports lipid content, lipid class composition and fatty acid profiles of each lipid class during the growth cycle of batch cultures of C. calcitrans. Total lipid content and the concentration of neutral lipid were highest in the late stationary growth phase (day 12). However, the amount of EPA was highest during the logarithmic growth phase (1.24 pg/cell on day 4). EPA was initially concentrated in the glycolipid fraction, but this fraction decreased during logarithmic growth, coinciding with the increase in neutral lipid. Docosahexaenoic acid (22:6n‐3, DHA) (0.91 pg/cell) was reported as a major fatty acid (>10 mg/100 g) in all lipid classes on day 1. DHA was depleted quickly from the neutral lipid and glycolipid classes, but at a slower rate from the polar lipid fraction. This work confirms that C. calcitrans is a good source of lipid, in particular EPA, for larval and adult filter feeders in aquaculture.     

Effects of diet and temperature on post‐settlement growth and survival of the short‐spined sea urchin Strongylocentrotus intermedius

Effects of diet and temperature on post‐settlement growth and survival of a sea urchin Strongylocentrotus intermedius, which fed on one of six mono‐cultured benthic diatoms, gametophytes of a brown alga Undaria pinnatifida, a green alga Ulvella lens plus mixed benthic diatoms, or no food at 6, 9, 12 and 15°C, were examined. Digestion efficiency (DE), ingestion rate (IR), excretion rate (ER) and digested cell content index (DCCI) of each diatom species were measured. Growth rates largely differed among the dietary treatments from 7 days post‐settlement. Sea urchins fed on a diatom Cocconeis sublittoralis showed considerably higher growth (7.85‐34.67 μm day^?1) than those fed on the other diets and high survival rates (100%). DCCI was also highest in C. sublittoralis. These results suggest that the quantity of diatom cell contents digested is an important factor affecting growth and survival of the sea urchins. Growth rates of sea urchins were higher in higher water temperatures, and significant differences in growth rate were observed between 6‐9 and 12‐15°C. ERs of C. sublittoralis were generally higher at higher temperatures, but DEs did not differ among the temperature treatments. Variations in growth rate among different water temperature appear to be caused by different food intakes of the urchins.     

Diatom Milking: A Review and New Approaches

The rise of human populations and the growth of cities contribute to the depletion of natural resources, increase their cost, and create potential climatic changes. To overcome difficulties in supplying populations and reducing the resource cost, a search for alternative pharmaceutical, nanotechnology, and energy sources has begun. Among the alternative sources, microalgae are the most promising because they use carbon dioxide (CO₂) to produce biomass and/or valuable compounds. Once produced, the biomass is ordinarily harvested and processed (downstream program). Drying, grinding, and extraction steps are destructive to the microalgal biomass that then needs to be renewed. The extraction and purification processes generate organic wastes and require substantial energy inputs. Altogether, it is urgent to develop alternative downstream processes. Among the possibilities, milking invokes the concept that the extraction should not kill the algal cells. Therefore, it does not require growing the algae anew. In this review, we discuss research on milking of diatoms. The main themes are (a) development of alternative methods to extract and harvest high added value compounds; (b) design of photobioreactors; (c) biodiversity and (d) stress physiology, illustrated with original results dealing with oleaginous diatoms.     

底栖硅藻生产性培养中的理论与实践

采用三种培养措施（Ⅰ.光照度2500-3000lx,一天一翻筐;Ⅱ.光照度2500-3000lx,3天一翻筐;Ⅲ.光照度1500-2000lx,3天一翻筐）进行底栖硅藻的生产性培养.结果表明:培养措施Ⅰ和Ⅲ获得的底栖硅藻种类组成(大型舟型藻、小型舟型藻、等片藻、菱形藻、直链藻、卵形藻的密度百分比分别为11.56±4.64,78.27±9.63,0.823±0.25,2.57±1.06,0.01±0.01,6.78±1.34和0.15±0.03,79.71±12.72,0.23±0.09,0.64±0.12,0.01±0.01,19.262±6.64)优于培养措施Ⅱ（大型舟型藻、小型舟型藻、等片藻、菱形藻、直链藻、卵形藻的密度百分比依次为23.56±10.47,38.47±9.85,22.51±9.86,10.24±2.86,5.22±1.68,0.007±0.002）,但培养措施Ⅲ所获得底栖硅藻总密度显著较低。说明采用较强的光照度（针对小型舟型藻类而言）结合每日翻筐的培养措施既能保证较优质的底栖硅藻种类组成,又提高了生长速度,迎合了水产经济动物苗种生产培养中对底栖硅藻的大量需求。     

Assessing the relative impacts of land‐use change and river regulation on Burdekin River (Australia) floodplain wetlands

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固定化菱形藻（Nitzschia sp.）的生长及营养成分变化

选用底栖硅藻菱形藻(Nitzschiasp.)为实验对象,分别研究了CaCl2浓度、胶珠直径、接种密度及胶珠密度对其生长的影响及后两因素对其主要营养成分含量变化的影响。结果表明:(1)随培养时间的延长,CaCl2浓度对菱形藻生长有极显著影响,在2%CaCl2溶液中形成的胶珠里菱形藻比生长速率最高;(2)胶珠直径对菱形藻在初期和指数期的生长影响显著,且较小直径(2.5～3.0mm)的胶珠较适宜菱形藻生长;(3)随接种密度和胶珠密度的提高,菱形藻的比生长速率都有先增高后下降的变化趋势,接种密度较高(2.50×104～5.50×104mL-1)时,固定化组的比生长速率是对照组的2倍左右。胶珠密度为220粒/(100mL培养液)左右较适宜(胶珠直径3.0mm);(4)初始接种密度和胶珠密度试验中,蛋白质、总糖及粗脂肪的含量固定化组低于或相当于对照组,而叶绿素的含量固定化组高于对照组。     

Production of diatom–bacteria biofilm isolated from Seriola lalandi cultures for aquaculture application

Controlled incorporation of selected microalgae and bacteria in aquaculture systems can be beneficial because they can act as microbiological control. That is why the characteristics of biofilm generated naturally in Seriola lalandi culture cages were analysed, their potential benefit to the growth of larvae was studied, and their controlled use for improving the larval viability and as a vector to improve incorporation of previously studied probiotic bacteria was tested. According to biodiversity results, these biofilms are composed of a diatom–bacteria mix showing a decrease in biodiversity in laboratory culture conditions being dominated by Navicula phyllepta and bacteria of the family Rhodobacteraceae. This can be produced on mesh substrates incorporated in bioreactors with rapid growth rate and adhesiveness. Preliminary results from the addition of substrates with this specific biofilm in larvae culture systems showed that it is consumed by the larvae without negative effects, while positive effects on the viability of larvae in combination with probiotics were observed. Considering preliminary results, the addition of these specific substrates with diatom–bacteria biofilms could be a good improvement for aquaculture systems and together with the use of probiotics can contribute to maintaining a stable and controlled system improving the viability of the larval fish culture in its early stages.     

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.