Holding Up the Line: RuBisCo

With all the extra CO2 we’ve been putting into the atmosphere since the Industrial Revolution, the age of global warming is finally upon us. In our scramble to find new sources of energy, some scientists have turned to algae. The logic is there: plants take CO2 and make O2. More plants = less CO2. It’s even carbon neutral! Problem solved, right?

A New Kind of Biofuel

Algae are a promising source of alternative fuel because, in the right conditions, they grow fast and don’t take up a lot of space. Anyone who has ever had to spend a Saturday afternoon scrubbing out a fish tank knows how annoying and stubborn algal growth can be. These green water-dwelling organisms are also photosynthetic, meaning growing them can help decrease atmospheric CO2 levels.

This looks yummy, doesn’t it?

Algae Cell Contents

Currently, many industries are already harvesting algal cell content for things like nutritional supplements and cosmetics. Algae also produce lots of polysaccharides. We can harvest these large molecules (and the cellulose from the cell walls) to ferment into ethanol fuel. The chemical reaction that drives all this is photosynthesis. RuBisCo, an enzyme in the light independent reaction is the catalyst that takes inorganic carbon (in the form of carbon dioxide gas in the atmosphere) and turns it into organic carbon (glucose).

More. Not Better.

It’s just quite unfortunate that RuBisCo is super inefficient. It’s also quite unfortunate that instead of evolving a better enzyme, plants do what the City of New York does for traffic and toll booths before the Lincoln Tunnel: add more lanes of traffic instead of making toll-paying faster. So yes, to make up for the fact that RuBisCo confuses CO2 for O2 a quarter of the time, plants just make more RuBisCo.

Green Algae Problems

If algae is so great, why aren’t we using more of it? Scientists who study algae as fuel have run into some of the following problems.

  • Only certain species can be used. It’s sort of the same reason why we domesticated horses, but not zebras. Zebras can’t be ridden (weak backs, apparently) and certain species of algae don’t produce enough polysaccharides.
  • It’s really expensive to grow algae. The setup to keep and grow them takes up a lot of space, land, and materials.
  • RuBisCo is slow which means photosynthesis is inefficient. You could grow lots of algae over acres of land and still not harvest enough polysaccharides for the whole operation to be worth it. Also, plants will shut down photosynthesis if there’s too much light, too hot, or too much CO2. Yes, they’re finicky too.
  • It’s really time consuming. Between the growing, processing, and fermenting… it’s just way, way, way cheaper to burn coal.

Everything Has A Price

Climate change is a serious problem. But since the world is driven by capitalism and money, scientists know that the best way to reduce our use of fossil fuels is to make renewable energy sources cheaper than coal and petroleum. In the end, we may find that the best thing to do is to use some combination of all renewable sources.