Published on April 11th, 2016 | by Tina Casey19
New Biofuel Leans On Slothy Algae With Promiscuous Enzyme
April 11th, 2016 by Tina Casey
At first glance, the common green microalgae Botryococcus braunii looks like a horrible biofuel candidate. It grows so slowly that it takes a week to accomplish what other species can do in a matter of hours. However, B. braunii has intrigued biofuel researchers for decades, and now a team at Texas A&M has unlocked the genetic mystery behind one of its secrets, a “promiscuous” enzyme that could enable it to spit out gasoline, kerosene, diesel and other fuels.
Biofuel: Not Dead Yet!
Food, land, and water resource issues have been bedeviling the global biofuel industry, but fuel from plants does offer the prospect of carbon neutral fuel production for gasoline, diesel, and jet fuel. After the corn biofuel debacle during the Bush Administration, researchers have been focusing on the oil production capabilities of algae and microalgae, as a non-food crop that could be grown in areas where water scarcity is not an issue.
Biofuel production also offers the potential for some intriguing piggyback operations, such as water desalination and food production, which have the potential to math out as carbon negative.
Here in the US, the Energy Department chopped funding for algae biofuel research in 1995, but it did fold its microbiology efforts into a new national collaboration called the Joint Genome Institute, and by 2010, volatility in the oil market provided the agency with a rationale to pump more dollars directly back into the field.
With an assist from other federal agencies (namely, the US Navy and National Science Foundation), the Energy Department continues to be all over algae biofuel, despite the fossil oil market crash. In February the National Renewable Energy Laboratory modeled a new “whole body” process that could help keep algae biofuel costs competitive against the floundering petroleum market.
In the most recent development, last February, the agency issued the third in a three-year series of multi-million dollar funding rounds for algae biofuel.
Why Botryococcus braunii?
The Joint Genome Institute has been focusing like a laser on Botryococcus braunii. Here’s the official line on the micro-algae’s attractiveness to researchers:
…Botryococcus braunii is found worldwide, but most notably in oil and coal shale deposits. Approximately 40 percent of the B. braunii cells is made up of hydrocarbons, and the oil produced can be easily converted and used for vehicle and jet fuels with more than 90 percent efficiency. B. braunii has been studied for several decades, not just for its potential as a source of biofuel, but for its ability to sequester carbon…
Did you catch that part about oil and coal shale? Oh, the irony!
The Texas A&M AgriLife Biofuel Research
That brings us to the new biofuel study, conducted by researchers at the Texas A&M AgriLife program. While mapping the biochemical pathway that enables B. braunii to produce an oil called lycopadiene, the team nailed down the enzyme that initiates the oil production process, encoded in a “very interesting” gene called lycopaoctaene synthase (LOS), as described by lead researcher Dr. Tim Devarenne:
A closer look at the LOS enzyme revealed that the enzyme is “promiscuous” in that it is capable of mixing several different substances, or substrates, to make different products.
As explained by the research team, promiscuity is a common trait among enzymes, but it is unusual to find this particular combination of hydrocarbon and enzyme. By mixing different substrates, LOS produces longer, more desirable carbon molecules of 35 and 40 carbons long:
…that’s not only different from other enzymes that are similar to LOS, but it’s important because most enzymes like LOS only use a 15-carbon substrate. In terms of fuel, it’s better to start with a higher carbon number molecule.
Don’t expect to fill ‘er up with B. braunii any time soon, though. This is just the “very first” step in the algae fuel production pathway, so there is a lot of gene mapping to be done.
Other challenges involve finding an efficient host organism to express the genes in order to maximize fuel production.
Finding a faster-growing host would also be helpful. According to the research team, B. braunii takes a full week to double its cells, a trick that other algae can accomplish in about six hours.
That seems like a tough row to hoe, but gasoline prices in the US have already begun inching up this year and the global climate is not getting any colder, so the prospects look good for more funding for algae biofuel research.
Image (cropped): via Texas A&M AgriLife by Kathleen Phillips.