I wanted to thank a member from the community who shared the article entitled: "Lipid productivity as a key characteristic for choosing algal species for biodiesel production" by Griffiths and Harrison (2009).

I really like this paper as it reviews several important aspects from strain selection to scale up summarized from the literature. Topics covered:

• Desirable characteristics of algae for mass culture
• Changes in algal taxonomy to be aware of when reviewing the literature
  
• A review of the average laboratory lipid content, biomass and lipid productivity for 55 microalgal species and genera in the literature
• Averages of laboratory lipid content under nutrient-replete and nitrogen-deprived conditions for algae and cyanobacteria
• The average lipid content and biomass productivity for microalgae grown in outdoor ponds and photobioreactors under nutrient-replete conditions
• Doubling times for algae and cyanobacteria

You will find the abstract below:

Microalgae are a promising alternative source of lipid for biodiesel production. One of the most important decisions is the choice of species to use. High lipid productivity is a key desirable characteristic of a species for biodiesel production. This paper reviews information available in the literature on microalgal growth rates, lipid content and lipid productivities for 55 species of microalgae, including 17 Chlorophyta, 11 Bacillariophyta and five Cyanobacteria as well as other taxa. The data available in the literature are far from complete and rigorous comparison across experiments carried out under different conditions is not possible. However, the collated information provides a framework for decision-making and a starting point for further investigation of species selection. Shortcomings in the current dataset are highlighted. The importance of lipid productivity as a selection parameter over lipid content and growth rate individually is demonstrated.

Melinda J. Griffiths and Susan T. L. Harrison. 2009. Journal of Applied Phycology. Volume 21, Number 5, 493-507, DOI: 10.1007/s10811-008-9392-7

"This review is focused on potential avenues of genetic engineering that may be undertaken in order to improve microalgae as a biofuels platform for the production of biohydrogen, starch-derived alcohols, diesel fuel surrogates,and/or alkanes."

Some of the commercialization challenges of algae based biofuel that this review article identifies include:

• A low-energy methods to harvest microalgal cells.
• The ability to consistently produce biomass at large scale under highly variable outdoor conditions.
• Preventing invasive species in large-scale ponds.
• The low light penetration in dense microalgal cultures.
• Having a cost effective extraction technique.
• Potentially poor cold flow properties of most microalgae based biodiesel.

Algae research efforts are making headway to address immediate needs of the algae sector. Screening different strains of algae is a logical first step to finding a strain that may be suited for a specific application. Here is where we currently stand.

• Over 40,000 species of algae have been described, and it is likely that this is only a small fraction of the total number of available species. (Source: Hu, Q., M. Sommerfeld, E. Jarvis, M. Ghirardi, M. Posewitz, M. Seibert,  and A. Darzins. 2008. Microalgal triacylglcerols as feedstocks for biofuel production: perspectives and advances. Plant J. 54:621-639)
• 3,000 strains of algae were investigated during the US. Department of Energy's Aquatic Species program. NREL and several other research institutions are continuing this screening effort.
  

While screening efforts have picked up in recent years, not all of this information will be public knowledge.

When we put algae into a commercialization context it will be incredibly fast compared to commercial agriculture. Commercial crops have been grown for thousands of years with specific traits being selected for and improved upon the entire time. A popular example is corn (maize).

In order to improve algae for industrial applications there are several areas that need to studied further. This review covers the following areas.

Genetic engineering of microalgae

• Microalgae genomes- While most algae research has been limited to a few strains of algae, lower costs in sequencing and their relatively small size will allow microalgae genomics to develop quickly. 
• Methods for transformation and expression- there have been over 30 different strains of microalgae that have been transformed successfully. The review notes that the "efficiency of transformation seems to be strongly species dependent."
  

Genetically engineering lipid metabolism in microalgae

• Lipid metabolism is discussed from the biosynthesis, catabolism, and pathway modification perspective. Boiling it down it would be ideal to be able to control all of the cellular machinery to produce lipids that are desirable for biofuel applications. This includes controlling the lipids produced, and trying to optimize cellular production of the desired product.
  

A one step biofuel production process

• Direct production of biofuel is discussed as a way of reducing production of costs of biofuels. Most successful examples of direct biofuel synthesis have thus far only been achieved in E. coli. This validates that it should be possible with algae with the right transformation tools.
  

The review also mentions examples and methods of secreting specific products from organisms are also discussed here as a way of addressing a major economic hurdle: harvesting algae cells Genetic modifications of carbohydrate metabolism and hydrogen production are also discussed. Finally, the review discusses improving the microalgae strains tolerance to environmental stresses (light is the main focus,  but other stresses include salt, pH, temperature, etc.)

While there is a lot of work that needs to be done in a number of areas, it is exciting and I am confident the algae sector (academic and industry) are making progressive steps in improving algae for biofuel production.

If you are interested in the review the abstract is shown below.

Genetic engineering of algae for enhanced biofuel production

Radakovits, R. Jinkerson, RE, Darzins, A, Posewitz, MC

There are currently intensive global research efforts aimed at increasing and modifying the accumulation of lipids, alcohols,hydrocarbons, polysaccharides and other energy storage compounds in photosynthetic organisms, yeast and bacteria through genetic engineering. Many improvements have been realized, including increased lipid and carbohydrate production, improved H2 yields,and the diversion of central metabolic intermediates into fungible biofuels. Photosynthetic microorganisms are attracting considerable interest in these efforts due to their relatively high photosynthetic conversion efficiencies, diverse metabolic capabilities, superior growth rates and their ability to store or secrete energy-rich hydrocarbons. Relative to cyanobacteria, eukaryotic microalgae possess several unique metabolic attributes of relevance tobiofuels production, including the accumulation of significant quantities of triacylglycerol, the synthesis of storage starch (amylopectin and amylose), which is similar to that found in higher plants, and the ability to efficiently couple photosynthetic electron transport to H2 production. Although the application of genetic engineering to improve energy production phenotypes in eukaryotic microalgae is in its infancy, significant advances in the development of genetic manipulation tools have recently been achieved in microalgal model systems, which are being used to manipulate central carbon metabolism in these organisms.It is likely that many of these advances can be extended into industrially relevant organisms. This review is focused on potential avenues of genetic engineering that may be undertaken in order to improve microalgae as a biofuels platform for the production of biohydrogen, starch-derived alcohols, diesel fuel surrogates,and/or alkanes.

PMID: 20139239