Benthic algae: the iPhone 4S of algae?

Introduction: the next generation of-next-gen biofuels
Algae are often billed as "next-gen" biofuels, because they're expected to surpass the productivity and envitronmental sustainability of first-generation biofuels based on corn and soy.  However, new research published in the journal AMB express suggests there's an even newer generation of biofuel on the horizon.  Will biofuels soon outpace Apple and its iPhones in terms of product cycles?  Only time will tell.

The problem: too much water
One major roadblock for producing algal biofuel is separating algae from the water in which they grow. To collect algae from current systems strategies like filtration, centrifugation, gravity, and evaporation are used.  Each of these approaches has its drawbacks, which result in increased cost of production.  Filters are expensive and need to be cleaned.  Centrifugation takes a lot of energy.  Gravity and evaporation take time and space that could be used for growing more algae. 

It takes a lot of energy to separate the algae from the water in this raceway system.

The new kid on the block: benthic cyanobacteria

Not all algae, however, grow as single cells in the water that need to be scooped up in some way.  Some algae scoop themselves up into large biological mats.  In July, three researchers from Cawthron Institute in New Zealand investigated three different species of benthic cyanobacteria that harvest themselves!  What are benthic cyanobacteria, you ask? Benthic organisms come from the seafloor or lake bed (the benthos). Cyanobacteria used to be known as blue-green algae until someone realized that they're in fact bacteria and not algae at all.  That said, they have very similar properties to eukaryotic algae.  For instance, they can turn CO2 into sugar and lipid using sunlight.  They can store other nutrients for use.  They are a potential feedstock for biofuels.

What makes these particular algae unique is their ability to grow in easily collectible mats.  However, as I've mentioned in previous posts, many wild organisms that look useful don't necessarily grow in culture.  Indeed most organisms (over 99%) don't grow in culture.  The challenge before these authors was finding the culture conditions that would produce the maximum amount of bacteria.

A mat of benthic cyanobacteria from New Zealand that has collected on a rock

The hunt for the substrate: what's handy?
The main challenge before the authors was finding a substrate for the bacteria to grow.  In order to figure this out, they literally just looked around the lab.  As you can see from the figure below, the authors just stuck common lab items into bioreactor bags and hoped something would stick.

The various conditions researchers tried to grow this new form of algae.  Panels A and B are bioreactors held horizontally or vertically.  Panel C is a bioreactor bag with silicone lab tubing.  Panel D is clearly just a bottle brush in a bag.  Panel E is another piece of silicone tubing folded in on itself.

The result: great green glop!
Surprisingly, the authors were able to find optimal growth conditions just by grabbing what's around.  It turns out the looped silicon grew 2 times more cyanobacteria than the other growth strategies.  That said, the final yield even from the best bioreactor was 7 times lower than growing normal algae in an open pond without CO2 amendment and far lower than growing normal algae in a photobioreactor.  I guess that's what makes this organism a next-generation next-gen biofuel.  If further optimization can occur (through improved culture conditions, genetic manipulation, further bioprospecting, or more), perhaps this cyanobacteria will outperform todays best algae.  

The cyanobacterium Phormidium autumnale after 36 days of growth in a photobioreactor in and out of water (a and b).

Laser algae?

A recent paper got me thinking about a far-out solution to a major challenge to industrial-scale algae production

PROBLEM: shallow light
For algae production, one major barrier between bioenergy yields that can be reached in theory (or even in the lab) and the yields achieved in the field is the penetrance of light into a pond. In the lab, a dense culture of algae gets exposed to more light through the turbulence of a constantly swirling flask. In a pond, only the algae at the surface get exposed to light and produce energy.
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light-blocking effect of photosynthetic algae. NPQ is nonphotosynthetic quenching; P is photosynthetic energy. (Melis 2009)

Industrial yields could improve if more algae could get access to more light.

THE PRACTICAL SOLUTION: cut the chlorophyll

About two years ago, Anastasios Melis proposed a counterintuitive, yet elegant, solution to this problem. He proposed to reduce the chlorophyll content in each algal cell. You see, a lot of light ends up hitting chlorophyll overloaded with photons. If the amount of chlorophyll is reduced, light can go deeper into a culture and charge more algae, possibly improving overall yield.

light-blocking effect reduced with less chlorophyll. NPQ is nonphotosynthetic quenching; P is photosynthetic energy. (Melis 2009)

THE FAR-OUT SOLUTION: laser algae
A recent article appearing in Nature photonics just totally blew my mind. They turned human cells into lasers! The authors simply over-expressed green fluorescent protein (GFP) in cells, pumped up the GFP with pulses of light, and the cells fired off laser light as a result. The authors and others have proposed to use this technology to get light to previously inaccessable places in human tissue, and to potentially activate light-sensitive drugs.

However, why not use this technology to get light deeper into an algal culture?

A human cell emitting laser light in a dish. (Gather MC and Yun SH 2011)








THE FAR-OUT PROBLEM: too much equipment
In order to get cells to fire like a laser, you can't just overexpress GFP. You need a big apparatus to complette the laser. In the original paper, cells were plased in a resonator chamber and the GFP was activated with pulses of light to pump up the laser and cause it to fire. This is obviously a little too equipment intensive for game time.

However, there are ways to get single cells to produce light. Indeed single cells do this readily in nature!

The entire apparatus for creating a cell-based laser. Bottom, a microscope pulses light at a cell (blue arrows) The cell (placed between rectangular resonators) emits laser light (green arrows). d=20 micrometers. (Gather MC and Yun SH 2011)








BACK TO EARTH: the lesson here

While writing this post, I realize that the idea of cell-based lasers is way too ridiculously crazy to ever be used to produce algae based biofuel. However, I think another lesson can be drawn from this paper.

These authors used commonly available biological reagents to accomplish extraordinary tasks. For instance, basically any cell biology lab can create a GFP cell like the one described in this paper, and many do every day. Yet, the authors were able to take a common reagent that people have used for almost 20 years and do something extraordinary with it.

Perhaps, there is hope for some existing reagent to do something incredibly cool with algae. Could expressing the luciferase gene make algae glow like fireflies and get more light to more cells? Could a common mitogen enhance their growth? What other common reagents are available that could boost the yield of industrial algal biofuels?

REFERENCES
Gather MC and Yun SH. "Single Cell Biological Lasers". Nature Photonics. volume 5 (2011): 406-410.

Melis A. "Solar energy conversion efficiencies to photosynthesis: Minimizing the chlorophyll antennae to maximize efficiency". Plant Science. volume 177 (2009): 272-280.