Benchtop biofuels: Helping cyanobacteria to flourish

July 9, 2010

Cyanobacteria are among the oldest living forms in nature, responsible for generating the atmospheric oxygen we breathe today. Now Hyun Woo Kim and Raveender Vannela, researchers at ASU's Biodesign Institute, are perfecting the means to culture these microbes – a potentially rich source of biofuels and biomaterials – in significantly greater abundance.

The work provides a vital foundation for optimizing a device known as a photobioreactor (PBR), in which these energy-packed photosynthetic organisms proliferate. Download Full Image

While a variety of candidates have been called into service for producing clean forms of energy to replace harmful fossil fuels – from corn ethanol to switch grass or various forms of algae – cyanobacteria offer a particularly attractive option.

As Kim explains, “cyanobacteria are much easier to re-engineer because we have a lot of knowledge about them. We can control their growth so that we can produce large amounts of biofuel or biomaterial.” (The team works at Biodesign’s Center for Environmental Biotechnology, under director Bruce Rittmann.)

The new research indicates that the optimization of cyanobacterial growth requires a delicate interplay of CO2, phosphorus and sufficient light irradiation, within the PBR vessel containing the microbial crop. The group’s foundational study provides quantitative tools for evaluating factors limiting production of cyanobacteria within PBRs – a critical step along the path to large scale biofuel production. Results appeared recently in the journal Biotechnology and Bioengineering.

Photosynthetic cyanobacteria are able to produce roughly 100 times the amount of clean fuel per acre compared with other biofuel crops, and because their survival needs are simple – sunlight, water, CO2 and a few nutrients – they do not require arable land to be taken out of food production. Rather, cyanobacteria can be grown in rooftop PBRs or wherever sufficient quantities of sunlight and CO2 can be provided.

As Vannela notes, “the PBR uses solar photons as an energy source to convert CO2 to reduced forms such as biomass, proteins, lipids and carbohydrates. It's a biological reactor, fixing solar energy into very useful forms of energy for human society.”

Cyanobacteria reproduce prolifically, achieving a high biomass yield and they are tolerant of a wide range of temperatures, salinities and pH conditions. In addition to biofuels, which are extracted from fat-containing lipids in the cyanobacteria, the microbes also can produce many chemically based materials useful for industrial applications, such as biopolymers or isoprenes. Photosynthetic microbes also are valuable for the growing field of neutraceuticals, permitting  the manufacture of anti-cancer agents from fatty acids or antioxidants like beta carotene.

For the current study, the group used wild type Synechocystis PC6803, cultured in a benchtop PBR, and supplied with the customary growth medium, known as BG-11. A series of semi-continuous experiments were conducted, in which three principle variables were manipulated and the resulting growth of cyanobacteria, observed. These were C02, light irradiance and phosphorus.

“In this study,” Kim notes, “we found that phosphorus is really important.” Indeed, the cyanobacteria were unable to make efficient use of carbon dioxide in their growth cycle until the BG-11 medium was supplemented with phosphorus. Augmenting the medium with additional phosphorus allowed higher biomass productivity in the bioreactor. Once the phosphorus limitation was overcome, light irradiance and CO2 became the limiting factors for growth.

While phosphorus content had been studied in the past with respect to the problem of eutrophication in lakes and other inland waters, its significance for controlled growth of phototrophs like cyanobacteria within a PBR had not been examined in detail. In a series of experiments, the team simulated the natural pattern of light irradiance produced by sunlight, while carefully controlling the levels of CO2  (applied at 2.5, 5.0 and 7.5 percent) and phosphorus.

Results showed that when all essential nutrients are supplied, light irradiance becomes the limiting factor, as the crowding of biomass within the containment vessel increasingly blocks available light to the cyanobacteria. This condition is overcome through periodic harvesting of biomass from the reactor. The advance of the team’s research was in quantifying these factors, in order to obtain optimal values for nutrients, CO2 and light irradiance. 

Vannela and Kim stress that while they supplied CO2 and nutrients including phosphorus to the PBR’s cyanobacteria in their experimental design, ultimately, the nutrient source could come from waste streams or be recycled from the harvested biomass, while the excess CO2 produced by power plants could fulfill the microbe’s respiratory requirements. Thus, a closed loop could be formed, generating useful energy from water contaminants and the CO2 currently contributing to greenhouse warming.

The work performed by the group is one component in a large, multidisciplinary effort to make eventual commercial-scale production of biofuels and biomaterials a reality. Such research seeks to address one of the most significant societal challenges – finding a carbon-neutral replacement for destructive (and dwindling) fossil fuels.

Written by Richard Harth,">
Biodesign Institute Science Writer

Lisa Robbins

Editor/publisher, Media Relations and Strategic Communications


ASU alumna named 2010 National Geographic Emerging Explorer

July 9, 2010

Arizona State University alumna Christine Lee has been selected as one of National Geographic’s 2010 Emerging Explorers for her bioarchaeological work investigating the mysteries of ancient China’s diverse populations.

Lee is currently an associate professor at the Research Center for Chinese Frontier Archaeology at Jilin University in China. She teaches graduate students physical anthropology – including dental anthropology, bioarchaeology and paleopathology – in English. In addition, she cleans and processes incoming skeletal collections from excavations and has participated in an excavation in Yunnan Province. A typical day for Lee includes analyzing skeletons from several archaeological sites in northern China, which she uses for her own research, as well as writing up osteological reports for the individual provincial archaeology institutes. Download Full Image

From an early age, Lee has been intrigued by bones. With a geneticist father and a nurse mother, she seemed destined for a career in a biological field.

“My father used to bring me to his laboratory on the weekends, and I used to play with the mice and rabbits used for cancer research. As I grew older, I became fascinated with bones and the information that could be learned from them,” she says, adding that as a child she asked family members to save bones from Kentucky Fried Chicken meals and Thanksgiving dinners so she could reconstruct the bird skeletons.

In college, Lee realized that she could use her interest in bones to earn a degree and study the past lives of people. So, she followed her bachelor’s in archaeology from the University of Texas at Austin with graduate school in bioarchaeology and physical anthropology at ASU’s School of Human Evolution and Social Change, graduating with her doctorate in 2007.

Physical anthropologist Donald Johanson, founding director of the Institute of Human Origins in the College of Liberal Arts and Sciences, was Lee’s dissertation committee co-chair. He remembers her as “one of those rare young scholars who clearly knew her goals and crafted a path of study that prepared her for success. She didn’t wait for opportunity to come to her but was proactive to create situations in which her scholarly tenets were appreciated and sought after for a variety of unique projects.”

Lee is working on a 2,000-year-old site in Qinghai Province involving soldiers who probably guarded the frontier between China and Mongolia. Next year, she will travel to Gansu to study excavated skeletons dating back 4,000 years. She will use her primary specialties of dental anthropology and paleopathology to study the population dynamics and health status of the peoples at these sites, thought to be ancestral to modern-day Tibetans.

Cassandra Kuba, chief forensic anthropologist for the Institute of Criminological and Forensic Sciences at the California University of Pennsylvania, has been a close friend of Lee since their graduate school days. Calling Lee one of the most intelligent and passionate people she knows, Kuba is hardly surprised by the Emerging Explorer designation. What does continue to surprise her is how quickly Lee took to her discipline and its often unglamorous demands. She explains, “Christine’s first venture into research in Asia was as the osteologist for an excavation team working in Mongolia. She is such a classy lady that I had a hard time envisioning her camping out on the steppes, eating marmot roasted by blowtorch or bathing in a glacier-fed stream.” But hearing Lee recount her experience and provide narration for the photos of her time in the field, Kuba “could not fail to recognize the joy she felt, reveling in the beauty of the land and its people.”

That ability to connect to people in the present and past is one of Lee’s special talents. She is respectful of each set of bones she researches and views them as human beings. She considers it part of her job to give these people dignity and their lives meaning by restoring their identity in some fashion. “I can’t help but wonder what their names were,” she confesses.

While she relates to all people she studies, Lee is especially touched by the remains of infants, children and those who suffered greatly in their lifetimes or in their manner of death. And some archaeological sites simply affect her more deeply than others. “I think that is based more on how the particular site and local people make you feel. I am always surprised when I see that the ancient faces are similar to the modern people. It helps me to picture a skeleton as a whole person instead of just a scientific specimen.”

Ultimately, Lee hopes to contribute significantly to filling what she sees as a dearth of physical anthropology research from China and Mongolia published in English. “I think there is a wealth of information from these regions that needs to be fitted into a global perspective,” she asserts. “I want the rest of the world to know about the people who lived here and be just as fascinated with them as the Romans, Egyptians, Maya or Inca.”

Lee is the first to admit that her field is a difficult one. Her advice to those considering a career in physical anthropology is detailed and well-thought-out. She says, “First of all, you really have to be devoted to the field. If you don’t have that, then you won’t make it through to the end.” Also important is contacting all of the professors whose research is relevant to a student’s interests, as these people can be future advisors and help a student make it through graduate school. She adds, “If you are interested in working in a foreign country, then learn the language as soon as possible and familiarize yourself with their culture. Get the best and broadest training you can. Go to the annual conferences and talk to professors and students. They can give you a clear perspective on what is going on in the field and which department is a good fit for you.”

Lee is one of 14 to receive the 2010 National Geographic Emerging Explorers honor, which carries a $10,000 award and supports extraordinarily talented up-and-coming researchers, adventurers and artists who have already contributed greatly to their fields. The recipients were announced in the June 2010 issue of National Geographic Magazine, and award-winner biographies appear on the National Geographic website:">

Rebecca Howe

Communications Specialist, School of Human Evolution and Social Change