Algal Oil Yields

Microalgae contain lipids and fatty acids as membrane components, storage products, metabolites and sources of energy. Algal strains, diatoms, and cyanobacteria (catagorised collectively as "Microalgae") have been found to contain proportionally high levels of lipids (over 30%). These microalgal strains with high oil, or lipid content are of great interest in the search for a sustainable feedstock for the production of biodiesel. As could be seen from Table 1, algae contain anywhere between 2% and 40% of lipids/oils by weight.

Comparison of average oil yields from algae with that from other oilseeds

The table below presents indicative oil yields from various oilseeds and algae. Please note that there are significant variations in yields even within an individual oilseed depending on where it is grown, the specific variety/grade of the plant etc. Similarly, for algae there are significant variations between oil yields from different strains of algae. The data presented below are indicative in nature, primarily to highlight the order-of-magnitude differences present in the oil yields from algae when compared with other oilseeds. ( see also: Vegetable Oils Yields & Characteristics – from Journey to Forever)

Yield of Various Plant Oils

Crop Oil in Liters per hectare

Castor 1413

Sunflower 952

Safflower 779

Palm 5950

Soy 446

Coconut 2689

Algae 100000

Lipid accumulation in algae typically occurs during periods of environmental stress, including growth under nutrient-deficient conditions. The lipid and fatty acid contents of Microalgae vary in accordance with culture conditions. In some cases, lipid content can be enhanced by the imposition of nitrogen starvation or other stress factors. Biochemical studies have also suggested that acetyl-CoA carboxylase (ACCase), a biotin-containing enzyme that catalyzes an early step in fatty acid biosynthesis, may be involved in the control of this lipid accumulation process. Therefore, it may be possible to enhance lipid production rates by increasing the activity of this enzyme via genetic engineering. 

The key question in everyone’s mind is: which is the best species of algae for biodiesel? The decades-long research undertaken by NREL of USA – called the Aquatic Species Program (see a copy of the Aquatic Species Program Research notes here, but please remember it is a large PDF file!) – did in-depth research on this topic and in the end has said that there is no one strain or species of algae that can be said to be the best in terms of oil yield for biodiesel. However they did conclude that the diatoms and secondly green algae were the most promising. 

Oilgae Digest - If you are keen to know more about the algae fuels industry, have you checked out the Oilgae Digest? It provides precise status information on the algae energy industry and will help you quickly understand the most important aspects of this exciting industry.

The following species listed are currently being studied for their suitability as a mass-oil producing crop, across various locations worldwide.

· Neochloris oleoabundans - A microalga belonging in the class Chlorophyceae

· Scenedesmus dimorphus - A unicellular algae in the class Chlorophyceae. While this is one of the preferred species for oil yield for Biodiesel one of the problems with Scenedesmus is that it's heavy, and forms thick sediments if not kept in constant agitation.

· Euglena gracilis

· Phaeodactylum tricornutum -A diatom

· Pleurochrysis carterae - A unicellular coccolithophorid alga that has the ability to calcify subcellularly. It is a member of the class Haptophyta (Prymnesiophyceae)

· Prymnesium parvum -A toxic algae

· Tetraselmis chui - A marine unicellular alga

· Tetraselmis suecica

· Isochrysis galbana - A microalga.

· Nannochloropsis salina – This is also called Nannochloris oculata. In the same group are Nannochloris atomus Butcher, Nannochloris maculata Butcher, Nannochloropsis gaditana Lubian, and Nannochloropsis oculata (Droop)

· Algal strains such as Botryococcus braunii can produce long chain hydrocarbons representing 86% of its dry weight. The green alga Botryococcus is unique in the quality and quantity of the liquid hydrocarbons it produces. Some scientists consider the ancestors of Botryococcus to be responsible for many of the world's fossil fuel deposits.

· Dunaliella tertiolecta - This strain is reported to have Oil Yield of about 37% (organic basis). D. tertiolecta is a fast growing strain and that means it has a high CO2 sequestration rate as well.

· Nannochloris sp.

· Spirulina species

The strains of Algae most favoured by the NREL researchers were Chlorophyceae (green algae). Green algae tend to produce starch, rather than lipids. Green algae have very high growth rates at 30^oC and high light in a water solution of type I at 55 mmho/cm.

The other algae favoured by NREL researchers is Bacilliarophy (diatom algae). However, the diatom algae needs silicon in the water to grow, whereas green algae requires nitrogen to grow^. Under nutrient deficiency the algae produced more oils per weight of algae, however the algae growths also were significantly less. While certain green algae strains are very tolerant to temperature fluctuations, Diatoms have a fairly narrow temperature range.

See also: Biodiesel Now Forum on Algal Strains

Oilgae Digest - If you are keen to know more about the algae fuels industry, have you checked out the Oilgae Digest? It provides precise status information on the algae energy industry and will help you quickly understand the most important aspects of this exciting industry.

Research into cloning the gene that encodes ACCase from the eukaryotic alga Cyclotella cryptica has been undertaken, by isolating this gene. Research found that the amino acid sequence of ACCase deduced from this gene exhibited a high degree of similarity to the sequences of animal and yeast ACCases in the biotin carboxylase and carboxyltransferase domains, but less similarity exists in the biotin carboxyl carrier protein domain. Comparison of the genomic nucleotide sequence to the sequences of cDNA clones has revealed the presence of two introns in the gene. Research teams are currently constructing expression vectors containing this gene and developing algal transformation protocols to enable over-expression of ACCase in C. cryptica and other algal species. 

Oilgae Digest - If you are keen to know more about the algae fuels industry, have you checked out the Oilgae Digest? It provides precise status information on the algae energy industry and will help you quickly understand the most important aspects of this exciting industry.

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