Can algae limit global warming?

Some diatoms are so small that 30 such individuals fit in a human hair width; but they also exist in tremendous numbers to become key players in the release of carbon dioxide from the earth's atmosphere.

The shells of diatoms are very hard, so when they die they often sink to the ocean floor to carry carbon from the water and hold them in layers of sediment at the bottom of the water.

Scientists have published their findings when studying gene and protein collections that control the shell creation program for each diatom species. For oceanographers, this study will one day help them understand how some issues such as global climate change can affect thousands of different diatoms as well as the ability to remove carbon dioxide in their atmosphere. Material scientists involved in the study are very interested in manipulating the silicon dioxide-producing gene, thus studying how to make a more efficient computer chip.

Thomas Mock, a postdoctoral researcher on the ocean and major author of the research report, said: "Most diatoms are too small and not visible without exaggeration;" but they play an amazingly important role in the global carbon cycle.During photosynthesis, diatoms turn carbon dioxide into organic carbon and release oxygen . Each year they contribute up to 40% of organic carbon produced in oceans around the world.

Thalassiosira pseudonana - Algae with shells of very hard silica look like a multi-hole box; size 3-4 micrometers and one of the smallest diatoms. (Photo: Washington University)

The team used the genetic map of diatoms Thalassiosira pseudonana published in 2004 by a team led by oceanography professor Virginia Armbrust - she also wrote for the PNAS newspaper. Sand algae Thalassiosira pseudonana is encased in a box-shaped shell with a very hard cell wall made up mainly of silicon dioxide and adorned with distinctive delicate dots to help scientists distinguish it from other algae. .

With a genetic map in hand, the researchers transformed the culture medium in the laboratory of Thalassiosira pseudonana; for example, limiting the amount of silicon or changing the temperature of the environment. They then used something called ' transcription gene segment ' to determine which gene segments would be activated.

Think of a tree placed on a windowsill with more sunlight than before. New living conditions will ' turn ' on or off the genes in that plant to adapt to the best increase in light intensity.

Since the late 1990s, scientists have only found some genes that affect the process of diatom formation. This study of Thalassiosira pseudonana algae has found large gene collections that were not previously known. For example, a set of 75 genes has been activated when silicon is restricted.

Scientists were also surprised to discover that another group of 84 genes was also activated when both silicon and iron were restricted ; This shows that there is a link between the two paths. Under low iron ratio, diatoms grow more slowly; The genes involved in the process of making silica shells are activated. Diatoms also tend to gather together under these conditions, making them heavier and easier to sink. Thick or thin cell walls depend on the amount of iron in the marine environment, but according to Mock, 'no one has a clue about the molecular mechanism of this'.

When up to 30% of the world's oceans are in serious iron deficiency, some scientists have suggested adding iron to these places so that diatoms can grow, increasing their numbers. and absorb more carbon dioxide from the atmosphere. Since then, global warming could be curbed. However, if iron is added to help diatoms increase the thickness of the shell, they will be difficult to sink while still floating in the upper water layer, where the carbon they store can be released back to the atmosphere when diatoms are eaten or decomposed.

Mock said: 'Iron may increase the number of diatoms but our study raises a concern about the effectiveness of this iron supplementation'.

Along with helping scientists find the cause of climate change as well as the ability to absorb carbon dioxide, diatoms also have a very special way to take advantage of silicon that engineers can only dream about.

Professor Michael Sussman of the University of Wisconsin, co-author of the study, said the new findings will help his team manipulate genes that govern silicon production and exploit those genes in production. circuit on computer chip. This technique can accelerate the microprocessor because diatoms are capable of producing circuits that are smaller than the existing technology.

The research is published online in The Proceedings of the National Academy of Sciences. The co-authors of the study are Vaughn Iverson, Chris Berthiaume, Karie Holtermann and Colleen Durkin (University of Washington); Manoj Pratim Samanta (Systemix Institute); Matthew Robinson, Sandra Splinter BonDurant, Kathryn Richmond, Matthew Rodesch, Toivo Kallas, Edward Huttlin and Franceso Cerrina (University of Wisconsin).

The research was funded by Gordon and Betty Moore Foundation, National Science Foundation, German Academic Exchange Service, National Institutes of Health Genomic Sciences Training Center and University of Wisconsin.