A key factor is determining the eco-friendliness of any biofuel is how much energy is required to produce it. If the energy expended in producing it, which more often than not comes from fossil fuels, is too high then the environmental benefits of the fuel can be questionable. Researchers have now developed a process that removes a key obstacle to producing lower-cost, renewable biofuels by programming a photosynthetic microbe to self-destruct.

Photosynthetic microbes, called cyanobacteria and also known as blue-green algae, have already proven attractive as a source of renewable biofuels because they are easy to genetically manipulate and have a potentially higher yield than any plant crops currently being used as transportation fuels.

But, until now, harvesting the fats from the microbes required many cost-intensive processing steps. Cyanobacteria have a multi-layer, burrito-like, protective set of outer membranes that help the bacteria thrive in even harsh surroundings, creating the pond scum often found in backyard swimming pools.

To get the cyanobacteria to more easily release their precious, high fat cargo, researchers Roy Curtiss and Xinyao Liu from Arizona State University (ASU), placed a suite of genes into the photosynthetic bacteria. The genes were taken from a mortal bacterial enemy, called a bacteriaphage, which infect the bacteria, eventually killing the microbes by causing them to burst like a balloon.

The scientists swapped parts from bacteriaphages that infect E. coli and salmonella, simply added nickel to the growth media, where the inserted genes produced enzymes that slowly dissolved the cyanobacteria membranes from within.

This is the first case of using this specialized bacterial system and placing it in cyanobacteria to cause them to self-destruct. "This system is probably one of a kind," said Curtiss, who has filed a patent with Xinyao Liu on the technology.

Curtiss and Liu are part of a large, multidisciplinary ASU team that has been focusing on optimizing cyanobacteria as a source of renewable biofuels. Arizona’s abundant year-round sunshine and warm temperatures are ideally suited for growing cyanobacteria, which is one of the reasons why the project was funded by Science Foundation Arizona, among others.

The next phase of the research is being funded by a two-year, US$5.2 million grant from the U.S. Department of Energy (DOE) led by researcher Wim Vermaas, Curtiss, Liu and others from the ASU biofuel team.

The team's research appears in the Proceedings of the National Academy of Sciences.