Green algae have worked to produce crude oil for millions of years. With a little help from biochemists, can they do the job much faster?
By ROBERT BURNS
Nature has used green algae for millions of years to produce the crude oil that humans refine to make gasoline and other fuels. Now biochemists are asking: Can humans modify these algae to produce fuel in months instead of eons?
“Oils from the green algae Botryococcus braunii can be readily detected in petroleum deposits and coal deposits, suggesting that B. braunii has been a contributor to developing these deposits and may be the major contributor,” says Timothy Devarenne, Texas AgriLife Research biochemist and assistant professor with the Department of Biochemistry and Biophysics, College of Agriculture and Life Sciences. “This means that we are already using these oils to produce gasoline from petroleum.”
Devarenne belongs to a team of scientists—representing AgriLife Research, the University of Kentucky and the University of Tokyo—that is trying to understand more about B. braunii, including its genetic sequence and its evolutionary history.
B. braunii offers a major advantage over other algae candidates, which produce vegetable oils but require specialized refinery processes. Existing oil refineries could process B. braunii oil with few modifications.
Unfortunately, B. braunii also has a severe limitation. Whereas the algae that produce vegetable-type oils may double their growth every six to 12 hours, B. braunii's doubling rate is about four days.
“Thus, getting large amounts of oil from B. braunii is more time consuming and more costly,” Devarenne says.
Making B. braunii more efficient by tinkering with its genetic code may offer a solution. “By knowing the genome sequence, we can possibly identify genes involved in cell division and manipulate them to reduce the doubling rate,” Devarenne says.
Only six species of algae have had their genomes fully sequenced and annotated, and B. braunii is not one of them. Devarenne and his colleagues have done some of the groundwork in better understanding B. braunii and sequencing its genome. They are working with the Berkeley strain of the B race of B. braunii, so named because the strain was first isolated at the University of California, Berkeley.
The team has determined the genome size and estimated the B race’s guanine–cytosine content, both of which are essential to mapping the full genome. Guanine–cytosine bonds are one base pair composing DNA structure. Adenine–thymine is the other possible base pair.
“Genomes with high guanine–cytosine content can be difficult to sequence, and knowing the guanine–cytosine content can help to assess the amount of resources needed for genome sequencing,” Devarenne says.
The team determined B. braunii's genome size to be 166 million base pairs. Compare that to the genome size of the common house mouse: about three billion base pairs. Despite its small size, the B. braunii genome is larger than any of the other six previously sequenced green algae genomes.
The team has submitted its groundwork to the U.S. Department of Energy’s Joint Genome Institute, which will carry out the actual genome sequencing and mapping.
“Without understanding how the cellular machinery of a given algae works on the molecular level,” Devarenne says, “it won’t be possible to improve characteristics such as oil production, faster growth rates or increased photosynthesis.”
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