Revolutionary step in the search for perfect algal strain

Developing better algae is a vital requirement in the quest to achieve sustainable algal biofuel. Now, researchers claim to have developed a new technology that could ‘revolutionise’ the search for the perfect algal strain – algal droplet bioreactors on a chip.

In the new technology, developed by researchers from the Boyce Thompson Institute and Texas A&M University, a single algal cell is captured in a tiny droplet of water encapsulated by oil. 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, forming 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, whereas previous work could only do one or the other," remarked senior author and engineer, Arum Han of Texas A&M University.

Although modifying algal genes can be relatively straight forward with the latest technologies, identifying which genes to target is time consuming and costly. When an algal culture is exposed to a mutagen it produces millions of unique, potentially improved cells that must be individually tested for the expression of a desired trait, such as increased lipid production. Mutated genes can then be 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 is 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.

Algae known to grow faster or slower, or produce more or less lipid, were used to validate the chip system. The researchers 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, representing total cell mass, and BODIPY, a fluorescent molecule that binds to lipids. All mutants with potential for improved growth or lipid production were recovered and verified off-chip.

Although promising, 200,000 is still a low number of mutants compared to what is needed to find the ‘super algal strain’.

“The most extraordinary variants will be found in one in a million, or ten million, so the throughput needs to be accelerated," explained senior biologist and BTI President, David Stern.

Significantly, the technologies needed to improve the throughput are already in development, including chips that can screen millions of droplets in one experiment.

"Such high-throughput technologies can rapidly accelerate the development process to obtain strains that are more efficient for use in biofuel production," Han remarked.

The research has been published in the journal Plant Direct.