A group of scientists from Arizona State University (ASU) have opened new doors to the production of renewable energy by generating a new biofuel synthesis method that is much cheaper and of higher yield.
For five years now, ASU Biodesign Institute researcher and microbiologist Roy Curtiss and his team have been developing cyanobacteria as feedstock in producing large-scale renewable and carbon-neutral fuels by genetic engineering. As a photosynthetic microbe, cyanobacteria require light, carbon dioxide, and water. Recently, the group has produced a heat-triggered, self-destruct method called thermorecovery that allows growth and production in the absence of light, a more favorable condition for industrial manufacturing.
In the previous years, the group has started with a method called green recovery, which is triggered by the removal of carbon dioxide to control the production of enzymes called lipases, which disrupt the microbes’ cell membranes and subsequently, releases their fatty acids, which can be finally converted to biofuels. However, when grown in bulk, these cyanobacteria become dense, covering up cells beneath and thus, hindering themselves from capturing optimum light.
For this reason, the group has aimed to achieve a more efficient and cheaper process than the light- and culture density- dependent green recovery. The new process, thermorecovery, utilizes a different type of lipases that are controlled by high temperatures, making it heat-triggered. These enzymes called thermostable lipases are synthesized by thermophilic (or heat-loving) organisms that grow in high-temperature environments such as hot springs.
The group has tested seven different thermostable lipases from microbes burgeoning in hot springs of temperatures 60oC to 70oC by swapping each lipase gene into the cyanobacteria strain that grows at lower temperature of 30oC. The modified strains of cyanobacteria were then subjected to production yield tests. First, to activate the gene that synthesizes the lipases, carbon dioxide was removed for one day.
Next, to maximize the activity of lipases, the strains were subjected to a temperature of 46oC for two days. Results showed that the highest yield of fatty acids was released by Fnl lipase from Feridobacteriumnodosum, an extremophile microbe that thrive in New Zealand hot springs.
In comparison to green recovery, thermorecovery process’ yield is 15% higher and 80% cheaper, and the productivity lasts for at least 20 days in a continuous semi-batch production. The promising new method is continuously improved and optimized by the research group.