Algal droplet bioreactors on a chip renew promises for algal biofuels

Algal droplet

Algae replicate quickly, requiring little more than water and sunlight to accumulate to massive amounts, which then convert atmospheric CO2 into oils that can harvest and readily processed into biodiesel. As new technologies emerge that might finally lead algal biofuels toward a competitive niche in the marketplace.

One of many improvements sustains production of algal bio-fuel is the development of better algae. Researchers explain the new technology may revolutionize the search for the perfect algal strain, Algal droplet bioreactors on a chip.

A single algal cell captures a tiny droplet of water encapsulated by oil. The tiny droplets form when you mix vegetable oil with water then millions of algal droplets squeeze onto a chip about the size of a quarter. Each droplet is a micro-bioreactor, a highly-controlled environment in which algal cells can grow and replicate for several days. The droplet forms a genetically homogenous colony that goes through its typical biological reactions, including the production of lipids.

"This is the first microsystem that allows both lipid content analysis and growth rate measurement at high throughput," remarked senior author and engineer, Arum Han of Texas A&M University.

Scientists identify a super algal strain that can reproduce faster and produce more lipids per cell. Researchers announced the discovery of a strain with a single genetic modification that allows much lipid production per cell.

gene-editing technologies

Today"s gene-editing technologies, modifying algal genes can be relatively straightforward; however, identifying which genes to target is time-consuming and costly. Exposing an algal culture to a mutagen yields millions of unique, potentially improved algal cells that must tested for expression of a desired trait, such as increased lipid production. Mutated genes can identified through whole-genome sequencing.

"The important thing is to develop a tool that can screen millions of cells in a much shorter time frame and a smaller space. In a chip housing millions of droplets of cells, each droplet like a flask or a bioreactor, and that"s how we can get results faster from just a tiny chip," explained author and BTI post-doc, Shih-Chi Hsu.

The researchers first validated the chip system with algae known to produce more or less lipid. They then screened 200,000 chemically mutated cells, identifying six mutants with both faster growth and higher lipid content. The screening, done on-chip uses fluorescence detection of chlorophyll, and BODIPY, a fluorescent molecule that binds to lipids. All mutants with potential for improved growth or lipid production recovered and verified off-chip.

While the results of this study promising, 200,000 mutants compared to what needed to find that super algal strain. "The most extraordinary variants found in one in a million, or ten million. So, the throughput needs to accelerate," explained senior biologist and BTI President, David Stern.

Excitingly, the tools improve throughput are already in development, including larger chips screen millions of droplets in one experiment. "Such high-throughput technologies can rapidly accelerate the development process to obtain strains more efficient for use in biofuel production," Han remarked.

With this discovery, commercial-scale production of biofuel from algae may finally be a realistic promise.

More information: [Plant Direct]