Fast-growth cyanobacteria gets thumbs up from scientists for biofuels production

Scientists from the US-based Pacific Northwest National Laboratory (PNNL) have discovered why the cyanobacteria called Synechococcus 7002 can produce high concentrations of biofuels.

The organism, commonly called a blue-green algae, triples in size to accommodate a rapid expansion of the cellular machinery it uses to build proteins, the workhorses of cells, according to the researchers. The organism flourishes under intense light by using the energy to keep growing.

Cyanobacteria capture the Sun's energy and use it to create food for themselves, all while drawing in carbon dioxide and giving off oxygen.  Carbon dioxide can be turned into glucose.

The single-celled organisms have been on Earth for billions of years and play a critical role in Earth's climate. Scientists are trying to take advantage of these natural processes to create new forms of energy and sustainable bioproducts.

"These organisms are the major pathway for capturing solar energy and carbon dioxide on our planet," said PNNL scientist Alexander Beliaev, one of two corresponding authors.

When light comes in too fast and too intensely for most cyanobacteria, they slow their growth, using their resources instead to repair damaged cells.

However, according to the scientists, Synechococcus sp. PCC 7002 is adept at using the extra light, doing chemistry on the fly and putting the extra energy to good use—toward rapid growth. The organism typically doubles in size in less than two hours, compared to other species which typically double between seven to 12 hours, the researchers said.

In a statement, the researchers said: “That may not sound like much. But if you start with a one-foot by one-foot plot of blue-green algae, after 48 hours the standard organism would cover the floor of a small office, while the fast-growth one would cover more than 600 football fields. That's an attractive difference for scientists trying to grow the organism as a source of fuel. The greater productivity means that more fuel and more chemical products could be produced more quickly compared to other systems.”

"Everyone's question is: How can we make affordable fuels and chemicals faster? It's a critical choke point for renewable biofuel processes," said Hans Bernstein, also a corresponding author. Fuels made of biological materials—such as ethanol—currently make up a small slice of fuels used today, largely because they are more expensive than traditional fuels.

 The new research is one step toward making a wider range of biofuels less costly and more attractive, the scientists explained.

Expanding the cellular machinery

The team led by Beliaev and Bernstein set out to understand the capability of Synechococcus 7002 for fast growth. They drew upon the resources of EMSL, the Environmental Molecular Sciences Laboratory—a Department of Energy user facility—to ferret out the molecular signals that underpin the organism's ability to stay productive even under bright light, using EMSL's capabilities to determine which genes were active.

Under bright light conditions where other cyanobacteria normally slow down, the team saw no hint of slowdown in the organism. Instead, the scientists demonstrated that the organism has the wherewithal to expand very rapidly, building molecular machinery quickly to convert light energy and carbon dioxide into new growth.

The scientists showed that the organism activates more of the genetic signals involved in creating the raw materials involved in building proteins in the cell. The activity of genes involved in building proteins, harvesting light, converting sunlight into food and taking up carbon dioxide all increased markedly. To accommodate the increased activity, the cells triple in size.