A cleaner way to unlock energy: microbes for biofuel

Oct 06, 2010 By Richard Harth
Cyanobacteria are capable of producing around 15,000 gallons of biofuel per acre - roughly 100 times that of plant or forest products including corn or switchgrass - and require only simple nutrients, sunlight and CO2 for growth. But prying out the cellular ingredients needed for biofuels has so far come at a steep price, both economically and environmentally.

Algae and photosynthetic bacteria hold a hidden treasure – fat molecules known as lipids – which can be converted to renewable biofuels. Such microorganisms offer an attractive alternative to the unsustainable use of petroleum-based fossil fuels, as well as biofuel sources requiring arable cropland.

Cyanobacteria are capable of producing around 15,000 gallons of per acre – roughly 100 times that of plant or forest products including corn or switchgrass – and require only simple nutrients, sunlight and CO2 for growth.

But prying out the cellular ingredients needed for biofuels has so far come at a steep price, both economically and environmentally. Chemicals traditionally used in the process are extremely toxic.

Graduate researcher Jie Sheng and his colleagues at Arizona State University’s Biodesign Institute, have been exploring new methods for performing lipid extraction by less harmful means. Under the guidance of Bruce Rittmann, director of Biodesign’s Center for Environmental Biotechnology, the team successfully tested several formulas that recover lipid with high efficiency. The group’s results appear in the current issue of Bioresource Technology.

The two best candidates for photosynthetic biofuel production – and cyanobacteria – may be readily refined to produce a range of green gasolines, diesels, and other biofuels. But as Sheng notes, cyanobacteria offer several crucial advantages as a lipid source. “Cyanobacteria, particularly the strain we use, (known as Synechocystis) are very simple and have been fully sequenced genetically, so that we can easily modify them.” Such genetic re-tooling would allow the quantity and quality of lipid production for biofuel to be optimized.

Further, unlike algae, which must be subjected to conditions of stress to maximize their lipid output, cyanobacteria are most successfully cultured under conditions of optimal growth, so that high-density lipid production is paired with a high rate of biomass production. “When the cell is provided with happy conditions for growth, we are able to get much more lipid out,” Sheng says.

But gathering the valuable lipids from cyanobacteria first requires the disruption of a tough, protective membrane. A half-century ago, Jordi Folch, a pioneering neurochemist, developed a method that remains the gold standard for isolating lipids from cells. The Folch method, as it is commonly known, has also been used by researchers to extract lipid from algae and cyanobacteria.

The technique involves the use of methanol and chloroform, which eat away and dissolve the lipids in a cell’s protective membrane, so that lipids may be harvested. For biofuel production, the Folch method is not practical, as large quantities of chloroform would wreak havoc on the environment and human health. (Chloroform, once a popular anesthetic, is categorized as a B2 chemical by the U.S. EPA – possibly carcinogenetic.)

Nevertheless, breaking down the durable thylakoid membrane of Synechocystis to get at the valuable lipids is not an easy task. As Sheng explains, alternate, less toxic chemicals have been used with success to extract lipid from algae, including ethanol, isopropanol, butanol, methyl tert-butyl ether (MTBE), acetic acid esters, hexane, and various combinations of these, but their viability for use with cyanobacteria was uncertain. Sheng’s team wanted to test such chloroform-free methods, to see if they could be used to extract lipids from Synechocystis.

In addition to the challenge of penetrating the more robust cyanobacterial cell membrane, Sheng notes that the lipids found in cyanobacteria are distinct from the lipids found in algae, vegetable and animal tissue, and the extraction methods may not work.

In a series of experiments, the team first demonstrated that the Folch method, as well as a closely related technique (Bligh & Dyer), were the most efficient means of lipid extraction for Synechocystis. Electron microscopy imaging showed effective penetration of the cell membrane and the ability to extract cyanobacterial lipids with high specificity.

The results closely matched the predictions the group had made through molecular modeling of the process. In contrast, ethanol, isopropanol, butanol, acetic ester, hexane, and combinations of these chemicals were significantly less effective in recovering lipid and were less specific, also recovering more impurities.

Intriguingly, the combination of methanol and MTBE showed high efficiency in cell penetration and lipid recovery, roughly comparable to the Folch and Bligh & Dyer methods. The group believes the combination of methanol and MTBE, which allows for the reduction of methanol and eliminates chloroform, may lower the toxicity and environmental impact of the extraction process.

The research was carried out through the collaborative efforts of biologists and engineers, and continuing work in conjunction with other teams at the Biodesign Institute will explore mutant strains of Synechosystis boasting much higher lipid yields than the wild variety used in these experiments.

Further studies, sponsored by Department of Energy, involve genetically modifying Synechosystis so that the portion of the lipid refined into biofuel – the fatty acids – may be directly secreted through the cell wall. These and other ongoing efforts are helping to advance biofuel production from benchtop to eventual commercialization.

Explore further: How steroid hormones enable plants to grow

Related Stories

Technology strikes a chord with algal biofuels

Sep 03, 2009

An award-winning Los Alamos National Laboratory sound-wave technology is helping Solix Biofuels, Inc. optimize production of algae-based fuel in a cost-effective, scalable, and environmentally benign fashion—paving the ...

Chemists get grip on slippery lipids

Aug 30, 2007

The ability of the body's cells to correctly receive and convey signals is crucial to good health. Lipids, or fats, play a critical role in this regulation by providing spaces for proteins to gather and network. They are ...

Recommended for you

Researchers discover new strategy germs use to invade cells

6 hours ago

The hospital germ Pseudomonas aeruginosa wraps itself into the membrane of human cells: A team led by Dr. Thorsten Eierhoff and Junior Professor Dr. Winfried Römer from the Institute of Biology II, members of the Cluster ...

Progress in the fight against harmful fungi

6 hours ago

A group of researchers at the Max F. Perutz Laboratories has created one of the three world's largest gene libraries for the Candida glabrata yeast, which is harmful to humans. Molecular analysis of the Candida ...

How steroid hormones enable plants to grow

Aug 19, 2014

Plants can adapt extremely quickly to changes in their environment. Hormones, chemical messengers that are activated in direct response to light and temperature stimuli help them achieve this. Plant steroid ...

Surviving the attack of killer microbes

Aug 19, 2014

The ability to find food and avoid predation dictates whether most organisms live to spread their genes to the next generation or die trying. But for some species of microbe, a unique virus changes the rules ...

Histones and the mystery of cell proliferation

Aug 19, 2014

Before cells divide, they create so much genetic material that it must be wound onto spools before the two new cells can split apart. These spools are actually proteins called histones, and they must multiply ...

User comments : 3

Adjust slider to filter visible comments by rank

Display comments: newest first

ereneon
not rated yet Oct 06, 2010
Just engineer the bacteria to secrete the lipids...
AJAYZ
not rated yet Oct 06, 2010
Note: Methanol, and hexane are fossil-fuel derivatives. So, ultimately what you need is a replacement for that, that is if you are concerned with being "green". Lipids (feedstock oils) are not so much a problem. However, what is a problem is glycerol, a byproduct of methanolic transesterfication, which produces FAME (biodiesel). Ultimately, what is needed is people to figure out a way to eliminate fossil fuel-derived reagents being used for biofuel production. If we can do that, then we can work to become sustainable. Ethyl acetate via Davy Protech (or something similar; see also Zeachem) can do this, when ethyl acetate produced via cellulosic ethanol production is used for "interestification" (making modified triglycerides). See "TBK Biodiesel" and tell them Andrew Blair sent you. There are solutions to sustainable biofuels, but people MUST make themselves aware of the real problems we face with with respect to commercializing biofuels like "TBK-Biodiesel"! TBK-Biodiesel!
rgharakh
not rated yet Oct 06, 2010
Can they freeze out the oil?