Algal Biofuel Production: The role of genetics
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Whilst advancements continue to be made in reducing costs of cultivation and simplifying downstream processes, some companies have favoured approaches involving genetically modified organisms (GMOs) or synthetic biology. The rapid advancement in this area over the last decade has enabled enhanced understanding of algal strains, improved productivity and the introduction of novel characteristics into new organisms. These biotechnological breakthroughs have been shown to have promising results in maximising overall biofuel yields and decreasing costs. Some companies have already claimed that through these methods, commercial sales of biofuels may not be too far from the future.
At present, GMOs are already in use in Canada, Brazil, Argentina, India and most notably America, the leading country for developments of biofuels from GM algae. Under new legislations passed by The European Parliament in January 2014, the UK will be able to decide whether GMOs can be grown in this country. Despite concerns expressed by campaigners against them, British scientists are fully behind the use of GMOs, which could see their introduction into the UK earlier than expected. This could have implications to the future production of biofuels in this country.
Whilst the use of GMOs remains to be an extremely controversial area, this page aims to provide a neutral and easy to understand explanation of how GMs can be used in algae biofuel production with consideration to their biosafety aspects.
The introduction of advanced screening methodologies such as genomics, proteomics and metabolomics have enabled scientists to gain a better understanding of the genetic make up of algal species. Not only has this allowed them to make better choices when it comes to selecting the algal strain but has allowed them to identify the expression of genes and understand what might limit important processes in the algal cells. Through advanced genetic engineering techniques, scientists have been able to improve certain pathways in algal cells as well introduce new or novel pathways into algae species which previously did not express a certain trait. With the use of these techniques it has been proposed that microalgae can be engineered to produce an increased yield, and in some cases quality, of lipids.
The sections below will give a brief summary of some published techniques in this fast growing area of science.
How can GM algae improve production?
Increased photosynthetic efficiency
Photosynthesis captures solar energy and stores it as chemical energy in the first stage of all biofuel production. Photosynthetic efficiency is the term used to explain how competently a photosynthetic organism is capable of capturing solar energy. An increase in this efficiency will ultimately result in improved growth and larger yields of lipids amongst microalgae species.
Most naturally occurring microalgae strains contain little structures within their cells known as light harvesting complexes or antennae. These structures capture sunlight and pass on the energy to other parts of the cell. In nature, this enables cells to maximise light capture when there is little light. However when grown in mass, for example in a photobioreactor, it has been shown that algae with smaller antennae have resulted in higher overall yields. By modifying the expression of the genes responsible for making the cell's antenna, scientists have been able to engineer algae that will only have small antenna. This enables a mixture with visibly lighter microalgae allowing light to penetrate further through the mixture reaching more cells. This has been shown to result in faster growth rates for improved production of biofuels.
Mixtures of wild type (non GM) algae and the same strain of algae modified with smaller antenna, allowing further light penetration.
Increasing plant productivity is a hugely fast growing focus of present day science. Not only could break throughs in this field have implications on plants for biofuels but could also have huge benefits to overcoming global concerns over food security. To learn more about this exiting area of science please follow the link below:
Increased lipid production
After photosynthesis, the next important function of the algae is to use the stored energy to make lipids. This involves a sequence of pathways and is collectively known as lipid biosynthesis. As more light is shed on how these pathways work and the key enzymes needed in lipid biosynthesis, there is increasingly excellent potential to modify these pathways to increase the production of lipids.
So far most of these techniques have focused on terrestrial plants. However many of the genes involved in lipid metabolism in land plants have descended from a common ancestor with microalgal species in their evolutionary history. The term given to these similar genes found in different organisms is 'homologs'. It is therefore probable that some of the GM techniques that have shown increased lipid metabolism in terrestrial plants will also be effective in microalgal species.
In the past GM techniques have focused on modifying important genes involved in lipid biosynthesis pathway. These genes may be either 'knocked out (made inoperative using certain methods) or overexpressed (expressing it more than normal). The overexpression of an enzyme, acetyl-CoA carboxylase, important to the first step of lipid biosynthesis, resulted in a minor increase in lipid synthesis in rapeseed.
Greater results, however, have been shown in overexpressing the enzyme glycerol-3-phosphate dehydrogenase (G3PDH), in plants from the same species. G3PDH catalyses the formation of an important molecule involved in assembling the fatty acids (lipids) that have already been formed in the cell. This study showed that using this technique, the lipid content of rapeseed was increased by 40%.
GM rapeseed with increased lipid content
Another possible method of increasing lipid content is by inactivating pathways important to the production of other energy rich compounds that serve no function in the production of biofuels. Results from previous studies have shown that inactivating pathways associated with the production of starch in the green algal species, Chlamydomonas reinhardtii. Using GM techniques to deactivate key enzymes involved in the metabolic pathway of starch, the algal species was able to conserve energy which would have otherwise been wasted on producing a product which is not useful for biofuel production. As a result, the GM algae showed increased yields of lipids.
In addition to engineering microalgae for increased lipid content, attempts have also been made to improve the quality of lipids in the terrestrial plants. The properties of the fatty acids categorises what fuel can be made from them. The length of a fatty acid as well as its saturation (i.e. whether if the carbon atoms in the chain are linked by single or double bonds) are key components to its functionality as a fuel. Engineering a microalgal species to directly produce a specific fatty acid profile, e.g. Shorter chain lengths for petrol and jet fuel production, may result in energy and cost savings in further downstream refining processes.
Simplifying extraction processes
The San Francisco based algal biofuel company Algenol have recently announced the opening of their first commercial algal biofuel facility in the US. Scientists at Algenol have engineered cyanobacteria species, cultivated in specialised photobioreactos, to produce ethanol directly. Using this patented technology they have been able to simplify costly downstream processes.
How does this system work?
This system relies on specific GM cyanobacteria strains used and cutting edge photobioreactors the algae are grown in.
The algae:
Much research over the past few years have focused on producing different types of biofuels from cyanobacteria with varying success. Using GM techniques, scientists at Algenol have introduced recombinant genes from the bacterium Zymononas mobilis (notable for its bioethanol production) into the genome of cyanobacteria. By introducing these genes they have been able to create an enhanced pathway for the production of bioethanol in cyanobacteria.
Further modification of the membranes of the cyanobacteria has enabled the ethanol to be transported from within the cell, across the membrane and into the mixture in the photobioreactor where it can be collected in the photobioreactor. This production system simplifies energy intensive extraction processes, ultimately reducing overall costs. The biomass which is left over can be converted into biodiesel and jet fuel through transeterification processes.
The photobioreactor:
The specifically designed photobioreactors are made from transparent plastic films. They allow sunlight to penetrate the algal cells within and consist of little ports which collect the ethanol as it is secreted from the cells and drops down into them.
Algenol's photobioreactors (courtesy of algaeindustrymagazine.com). To learn more Algenol's direct to ethanol system, click on the link below for a short video:
Solazyme: fermentation of GM algae
US based company Solazyme, have developed a cutting edge technique of producing renewable diesel and jet fuel from algae in customly built fermentation tanks. Unlike traditional systems which rely on exposing algal species to sunlight, Solazyme have successfully produced oil from algae under dark conditions in a process known as fermentation. During this process, algae inside the steel contatiner are fed a variety of low cost sugars. The key to the success of this system is the GM algae used. Solazyme have engineered strains of algae capable of converting specific sugars into desired oils in a novel way to the organism.
An example of one of their patented techniques is the engineering of a microalgae species to convert the woody sugar, xylose, into oils during fermentation. Normally this process would result in the production of an alcohol and not an oil. Through engineering of other species to convert other sugars, solazyme have created a flexible system in which a variety of different sugars can be added to the tank to yield oils with different properties. Once extracted, these oils can be used to create sustainable biofuels such as biodiesel and jet fuel as well as a number of high-value by products.
In 2011, United Airlines flew the world's first commercial flight run on jet fuel derived from algae. This fuel was derived from Solazyme's renewabale jet fuel produced in this way. Since then, Solazyme have also formed partnerships with the US military with the aim of providing high grade fuel from renewable sources.
Photo courtesy of fs2000
High value by-products
Solazyme's innovative technology has enabled the company to subsidise overall biofuel production costs through the manufacturing and sales of high value by-products. Applications of these lipid based by-products range from uses in cosmetics, high grade industrial oils as well as dietary supplements.
Similarly to integrated systems, combing biofuel production with other commercial enterprises, provides a promising way of manufacturing affordable and sustainable biofuels and could provide significant opportunities in the future.
To learn more about Solazyme, take a look at this short video:
GM Safety
Whilst GM technology provides great hope in overcoming some of the huge problems facing society, many people still remain sceptical about there safety. The use of GMOs in agriculture are widely debated and likely to be the focus of much interest over the next few years as legislations are lifted on the use of GM crops in the UK.
With the proposal of GMOs in large scale production systems of algae, huge considerations must be taken to the safety of their use. There are a number of methods deployed to eliminate the possibility of causing adverse effects. To understand the potential risks GM algae may pose on the environment and human health and what precautions are in place to mitigate these risks, please follow this link: