15%CO2胁迫下雨生红球藻积累油脂制生物柴油

采用经60Co-γ射线核辐射诱变和15%CO2驯化后的雨生红球藻突变藻株为对象,研究15%CO2对雨生红球藻制备生物柴油潜力的影响。结果表明:随着高光照和15%CO2协同胁迫时间的延长,油脂合成相关乙酰辅酶a羧化酶、β-酮酰基-ACP缩合酶Ⅲ和二酰基甘油酰基转移酶相对表达量分别提高至初始水平的1.2、1.4和1.3倍。15%CO2胁迫下雨生红球藻饱和油脂含量由2%CO2条件下的33.0%升至35.2%。15%CO2胁迫下雨生红球藻细胞孔径增大15%,孔面积增加2.3倍。萃取虾青素后的雨生红球藻渣亲水性指数为4.98,高于未处理生物质的亲水性指数。差示扫描量热分析(DSC)结果表明,藻渣制备的生物柴油的结晶度和熔点分别为-1.3℃和6.1℃。     

氮缺乏条件下小球藻碳水化合物与脂肪酸的合成规律研究

以小球藻Chlorella zofingiensis为研究对象,分析其体内两个次级代谢产物(脂肪酸和碳水化合物)在氮缺乏条件下的合成规律。研究结果表明,氮缺乏时C.zofingiensis在2 d内仍能继续生长,伴随着叶绿素含量的急剧下降。细胞的最初响应是在1 d内大量合成碳水化合物,含量从初始的48.4%增至66.9%,之后碳水化合物部分降解,而脂肪酸持续增长,含量从最初的6.2%增至24.5%。此外,研究还发现氮缺乏后饱和脂肪酸和单不饱和脂肪酸含量增大,而多不饱和脂肪酸含量有所减小。推测碳水化合物可能作为短期应急响应用于藻从逆境中快速恢复,而随着胁迫的延长,藻倾向于积累能量密度更高的脂肪作为长期储能物质。     

低氮胁迫对两种魏氏藻生长和油脂积累的影响

为了评价低氮胁迫对真眼点藻纲的两株高产油微藻(斧形魏氏藻和点状魏氏藻)的生长和油脂积累的影响,实验设计中将原改良BG-11培养基中的硝酸钠浓度降低为3.6 mmol/L(0.3 g/L)。结果表明:在此浓度下斧形魏氏藻和点状魏氏藻的最高生物量分别为8.21 g/L和9.07 g/L;两者的总脂、中性脂和总脂肪酸含量(占干重)都随着培养时间的延长而不断增加,培养至第18天时分别达到56.4%,64.7%;54%,63.3%;43.5%,45.5%。这两种微藻的主要脂肪酸都含有豆蔻酸、棕榈酸、棕榈油酸、油酸、亚油酸、花生四烯酸和二十碳五烯酸,均适合于生物柴油的生产。它们的总脂、中性脂和总脂肪酸的单位体积产率分别为0.257 g/(L·d),0.326 g/(L·d);0.246 g/(L·d),0.319 g/(L·d)和0.198 g/(L·d),0.229 g/(L·d)。这说明两种微藻在低氮胁迫下都能够获得较高的油脂产率。     

一种优化Botryococcus braunii-357生物膜油脂的方法

脂肪酸的组成与结构是影响微藻生物柴油物理特性的重要因素。胞外聚合物(EPS)有助于微藻吸附生长和生物膜的形成。为了研究EPS对微藻生物膜油脂含量及脂肪酸组成的影响,对布朗葡萄藻生物膜进行EPS刺激培养,同时设计营养抑制组作为对照。结果显示:抑制组和EPS组的油脂含量分别由16.54%提高至42.2%和51.3%,油脂的中性三酰甘油酯(TAG)占比均达93%左右,饱和脂肪酸分别占55.4%,62.6%,不饱和脂肪酸分别占38.7%,31.0%。不饱和脂肪酸方面,抑制组的油酸分子均为反式结构,EPS组均为顺式结构。用EPS刺激生物膜藻体,所得微藻油的油脂含量、纯度、日产率以及TAG比例都得以提高,油脂脂肪酸组成和品质得到改善。     

纤维藻培养及制备生物柴油的研究

探讨了纤维藻(Ankistudesmus sp)的低成本培养模式,考察了氮源和碳源以及反应器形式对纤维藻生物量、油脂积累以及油脂组成的影响。户外培养纤维藻在氮饥饿条件下油脂产率较高;通过槽式反应器和管式反应器的比较发现:槽式反应器更适合微藻的大规模培养;混养培养时能显著增加纤维藻的生物量和油脂含量,最佳添加条件下藻的生物量和油脂含量分别高达1.64 g/L和15.9%,1.41 g/L和11.9%。藻油经酸催化甲酯化制备生物柴油,经气相色谱分析,藻油主要成分为棕榈酸、油酸和亚油酸。氮缺陷、流加葡萄糖培养得到的纤维藻油含有25.32%的棕榈酸、44.74%的油酸,其制备得到的生物柴油具有更好的氧化稳定性和低温流动性。     

缺氮培养对小球藻碳水化合物和油脂积累的影响

以小球藻Chlorella sp.为研究对象,对比其在缺氮培养和富氮培养条件下碳水化合物和油脂积累的代谢改变。结果表明,缺氮后细胞生长受到抑制,比生长速率从正常培养的1.02 d~(-1)降至0.48 d~(-1)。细胞在缺氮第1天积累大量碳水化合物(66.9%干重),且主要以淀粉的形式存在。同时,缺氮诱导了油脂的积累,但明显落后于淀粉。通过对油脂组分的分析,发现在富氮条件下油脂的主要成分为糖脂,占总脂的51%,而缺氮后中性脂成为主要油脂组分,占总脂的87%。从原料品质角度,缺氮小球藻更适合生物乙醇和生物柴油的生产。     

富油微藻——尖状栅藻生物质生产与奶牛场废水处理相结合的效果研究

尖状栅藻(Scenedesmus acuminatus)是一株新近分离的富含油脂淡水绿藻,分别选用4种不同NaNO3初始浓度的BG-11培养基和4种不同浓度的奶牛场废水,在Φ3.0 cm柱状光生物反应器中对其进行培养。试验结果显示,在BG-11培养组中,NaNO3初始浓度为6.0mmol/L时尖状栅藻的生物量最大,达到9.5 g/L;3.6 mmol/L时总脂含量最高,为藻体干重的62.6%。在废水培养组中,100%废水培养时藻生物量最大,达到12.2 g/L;25%的废水培养时总脂含量最高,为藻体干重的62.4%;尖状栅藻的脂肪酸碳链长度为14~18 C,与石化柴油的平均碳链长度十分相近;在培养过程中该藻能有效地去除废水中的氮和磷,去除效率分别达到93.2%和99.4%。利用奶牛场废水培养富含油脂的尖状栅藻(S.acuminatus)不仅能够有效去除废水中的氮和磷等营养成分,还能为生物柴油生产提供有价格竞争优势的原料。     

光强与氮源对绿球藻GN38生长和油脂积累的影响

光强与氮源是影响微藻生长与物质积累的重要因子,文章研究了光强、氮源、氮源浓度对一株自然条件下分离的绿球藻GN38的生长和油脂积累的影响。实验通过在不同光照强度(179μmol/m2·s-1和84μmol/m2·s-1)条件下,分别以具浓度梯度(1N,1/3N,1/5N)的NaNO3和CO(NH2)2为氮源培养绿球藻,获得了GN38生长与产油的较佳条件。结果表明,较高光强能促进GN38生长和总脂积累;CO(NH2)2有利于GN38积累油脂;不同氮源均表现出氮源浓度与生物量成正比,无氮组除外;179μmol/m2·s-1光强、1/5N时GN38的总脂含量最高。综合考虑,产油微藻GN38的最佳培养条件为179μmol/m2·s-1光强和0.528 g/L CO(NH2)2,在此条件下干重达到6.7g/L,总脂含量为38%,总脂产量为2.54 g/L,脂肪酸成分中C16和C18含量高达95.15%。实验为该藻的后续深入研究及产业化培养奠定了基础。     

启动子对蓝藻合成乙醇能力影响的研究

从集胞藻PCC6803中克隆了Prbp1,Prnpb和PnrtA3个启动子,用于控制蓝藻中乙醇合成相关酶的表达,分别构建了3个基因工程藻株Syn-ZG72,Syn-ZG73和Syn-ZG74。在相同培养条件下,与之前构建的携带Prbc启动子的Syn-ZG25相比,Syn-ZG73乙醇产量与之相当,明显高于Syn-ZG72和Syn-ZG74,表明Prnpb的表达效果强于Prbp1和PnrtA。Prbp1不能控制乙醇的诱导合成,PnrtA可以控制乙醇的诱导合成,但是启动子强度弱,乙醇产量低。     

富含碳水化合物微藻的筛选、鉴定及其在不同氮浓度条件下的产糖分析

以实验室保存的4株藻株为研究对象,分析了它们的生长速率和淀粉等糖类的含量,其中1株富含碳水化合物的微藻 #3,其生长速率和淀粉含量分别可达0.086 g/(L•d) 和225.2 mg/L。18S rDNA聚类分析表明,其属于栅藻科链带藻属Desmodesmus sp。缺N条件下,微藻生长速率慢,总糖积累快;而在其他不同N浓度条件下,生长速率趋势一致,总糖积累速度不尽相同。     

Culture of microalgal strains isolated from natural habitats in Thailand in various enriched media

Six freshwater microalgal strains in the class of Chlorophyceae, including Chlorococcum humicola, Didymocystis bicellularis, Monoraphidium contortum, Oocystis parva, Sphaerocystis sp., and Scenedesmus acutus were isolated from natural habitats in Thailand. The six strains were compared for their biomass yield, lipid content, and lipid productivity in four enriched culture media in batch mode. Significant differences were found across algal strains and culture media. The best strain was found to be C. humicola, which had the highest biomass yield of 0.113 g/l/d (in Kuhl medium), the highest lipid content of 45.94% (in BG-11 medium), and the highest lipid yield of 0.033 g/l/d (in 3NBBM medium). The 3NBBM medium, which has the lowest nitrogen concentration among the four culture media, was considered the optimal culture medium for C. humicola for lipid production. The fatty acid profile of C. humicola was also found to be affected by the culture medium. More oleic acid (C18:1) but less linolenic acid (C18:3) was accumulated in BG-11 and 3NBBM than in Kuhl and N-8 media. Lipid profiles of C. humicola were comparable to palm oil in the percentage of palmitic acid and the total amount of saturated fatty acids; however, C. humicola made more poly-unsaturated fatty acids such as linoleic (C18:2) and linolenic (C18:3) acids than oil palms. Lipids from C. humicola were believed to be acceptable for biodiesel production.     

Expression profiles of genes involved in fatty acid and triacylglycerol synthesis in developing seeds of Jatropha (Jatropha curcas L.)

Jatropha (Jatropha curcas L., Euphorbiaceae), a potential biodiesel plant, has created tremendous interest all over the world for the use of its seed oil as a commercial source of biodiesel. Due to the unreliability of oil content in its seeds and low economic returns planting of jatropha in agriculture was restricted. Investigating the molecular basis of storage lipid accumulation during seed development is an immediate need to understand genetic factors regulating storage lipid biosynthesis in jatropha seeds. In this study, we characterized the seed development and lipid accumulation from female flowers pollinated to mature seeds, and investigated temporal expression profiles of 21 lipid genes involved in different steps of the pathways leading to fatty acid and TAG synthesis within jatropha developing seeds using quantitative real-time PCR technology. Concomitantly, 17 genes increased their expression levels in developing seeds compared to their expression in leaf, but showed various temporal expression patterns and different relative-maximum ratio ranging from 2.8 to 1,919,280-fold in developing seeds. Five gene groups with distinct temporal patterns were identified by clustering analysis of expression data. Two gene groups including 15 genes presented up-regulated expression patterns correlated with storage lipid accumulation in developing seeds. This study provided not only the initial information on promoter activity for each gene, but also a first glimpse of the global patterns of gene expression and regulation, which are critical to understand the molecular basis of lipid biosyntheses, identifying the rate-limiting genes during seed development and to create improved varieties by genetic engineering.     

Microbial oil production from thermophile cyanobacteria for biodiesel production

Compared to lipid extraction from algae, little work has been performed for cyanobacteria. In this article it is aimed to show high lipid accumulation potential of Synechococcus sp., Cyanobacterium aponinum and Phormidium sp. cells in BG-11 medium. Four different pH values (6–9) and NaNO₃ (0.25, 0.5, 1.0, 1.5 g/L) concentrations were examined at different incubation days to discover the highest lipid accumulation. The maximum lipid content could be achieved in the medium containing 0.25 g/L NaNO₃ at pH 7 for Synechococcus sp., pH 8 for C. aponinum and pH 9 for Phormidium sp. after 15 days. The maximum lipid contents and C16 and C18 methyl ester yields were measured as 42.8% and 46.9% for Synechococcus sp., 45.0% and 67.7% for C. aponinum, 38.2% and 90.6% for Phormidium sp. The saturated compounds were 74.5%, 77.9%, 84.7% for Synechococcus sp., C. aponinum and Phormidium sp., respectively. These crude lipids could be promising feedstock for biodiesel production.     

Biomass and lipid production of marine microalgae using municipal wastewater and high concentration of CO2

In order to reduce the cost of the production of microalgae for biodiesel, the feasibility of using the mixture of seawater and municipal wastewater as culture medium and CO₂ from flue gas for the cultivation of marine microalgae was investigated in this study. Effects of different ratios of municipal wastewater and 15% CO₂ aeration on the growth of Nannochloropsis sp. were examined, and lipid accumulation of microalgae was also studied under nitrogen starvation and high light. It was found that optimal growth of microalgae occurred in 50% municipal wastewater, and the growth was further significantly enhanced by aeration with 15% CO₂. When Nannochloropsis sp. cells were transferred from the first growth phase to the second lipid accumulation phase under the combination of nitrogen deprivation and high light, both biomass and lipid production of Nannochloropsis sp. were significantly increased. After 12 days of the second-phase cultivation, the biomass concentration and total lipid content increased from 0.71 to 2.23 g L⁻¹ and 33.8–59.9%, respectively. This study suggests that it is possible to utilize municipal wastewater to replace nutrients in seawater medium and use flue gas to provide CO₂ in the cultivation of oil-bearing marine microalgae for biodiesel.     

Comparison of dairy wastewater and synthetic medium for biofuels production by microalgae cultivation

This study is concerned with comparing raw dairy wastewater (DWW) with blue-green medium (BG11 medium) for biofuel production. Three microalgae strains (Chlorella sp., Scenedesmus sp., and Chlorella zofingiensis) were cultured in tubular bubble column photobioreactors with two media separately. After 8 days of cultivation, DWW was demonstrated to be more suitable medium for microalgae biomass and lipid production than BG11 medium. The biomass and lipid produced within wastewater provided suitable feedstocks for anaerobic digestion and biodiesel conversion. Nutrients in wastewater were efficiently removed (>90% total nitrogen removal, approximately 100% ammonia removal, and >85% total phosphorus removal) during this process.     

Identification of fatty aids through cultivation of Scenedesmus sp. from the Caspian Sea

Biomass concentrations of Scenedesmus sp. with variation of light intensities and nitrogen sources were investigated. At the end of the cultivation period, maximum biomass concentration was recorded under nitrogen deficiency and low illumination (1,000 lux), which was about 3-fold higher than other conditions. However, applying high illumination (6,500 lux) did not significantly boost the biomass concentration. At desired illumination, the fact was revealed that the excessive amount of nitrogen source may waste the chemical and financial resources. The presence of C16:0, C18:1, C18:2, and C18:3 as the major constituents (81.84% of the algal oil) makes Scenedesmus sp. biomass a suitable feedstock for biodiesel production.     

Exoelectrogens in microbial fuel cells toward bioelectricity generation: a review

Exoelectrogens are catalytic microorganisms competent to shuttle electrons exogenously to the electrode surface without utilizing artificial mediators. Diverse microorganisms acting as exoelectrogens in the fluctuating ambience of microbial fuel cells (MFCs) propose unalike metabolic pathways and incompatible, specific proteins or genes for their inevitable performance toward bioelectricity generation. A pivotal mechanism known as quorum sensing allows bacterial population to communicate and regulates the expression of biofilm‐related genes. Moreover, it has been found that setting the anode potential affects the metabolism of the exoelectrogens and hence the output of MFCs. Microscopic, spectrometry investigations and gene deletion studies have confirmed the expression of certain genes for outer‐membrane multiheme cytochromes and conductive pili, and their potential roles in the exoelectrogenic activity. Further, cyclic voltammetry has suggested the role of multifarious redox‐active compounds secreted by the exoelectrogens in direct electron transport mechanisms. Besides, it also explores the various mechanisms of exoelectrogens with genetic and molecular approaches, such as biofilm formation, microbial metabolism, bioelectrogenesis, and electron transfer mechanisms from inside the exoelectrogens to the electrodes and vice versa. Copyright © 2015 John Wiley & Sons, Ltd.