Algae biofuels and the Prisoner’s Dilemma

March 28, 2013 |

nash-croweCould new advances based around the old Prisoner’s Dilemma make algae biofuels cost-competitive, sooner?

Appears so, according to new research.

In the days before the internet, librarians knew that no two books were more dog-eared and caused more disappointment to callow youth that John von Neumann’s The Theory of Games and John Maynard Smith’s The Evolution of Sex.

They turned out to be about the nexus between mathematics and economics, and between math and biology than, as was usually surmised, about Space Invaders, Asteroids, Donkey Kong and girls.

But they did provide an introduction to the world of non-cooperative game theory — and it is fascinating to discover that algae researchers have lately begun to describe limitations in the production of algae for biofuels in ways that can best be understood as the Prisoner’s Dilemma.

60 Second Primer on the Prisoner’s Dilemma

Albert Tucker first described the Dilemma thus:

Two members of a criminal gang are arrested and imprisoned. Each prisoner is in solitary confinement with no means of speaking to or exchanging messages with the other. The police admit they don’t have enough evidence to convict the pair on the principal charge. They plan to sentence both to a year in prison on a lesser charge. Simultaneously, the police offer each prisoner a Faustian bargain. If he testifies against his partner, he will go free while the partner will get three years in prison on the main charge. Oh, yes, there is a catch … If both prisoners testify against each other, both will be sentenced to two years in jail.

In graphic terms it is presented as:

Prisoner B stays silent 

Prisoner B betrays 

Prisoner A stays silent 

Each serves 1 year

Prisoner A: 3 years

Prisoner B: goes free

Prisoner A betrays

Prisoner A: goes free

Prisoner B: 3 years

Each serves 2 years

The problem — even though the prisoners mutually benefit from silence — prisoner A reasons that, no matter what the prisoner B does, he himself does better by betrayal. And vice versa.

Let’s now apply the problem to the world of algae biofuels.

One thing that researchers puzzle over is the problem of light harvesting and light processing. Frankly, little algae critters are light hogs — able to capture almost 100% of the light coming their way via these microscopic photon-capturing antennae they have. But they waste up to 75 percent of that light because, as it turns out, they don’t have the ability to process all that light into energy, and most of it is dissipated as heat or florescence.

Optimizing algae’s light distribution

Much of this is explored in the excellent “Optimization of photosynthetic light energy utilization by microalgae,” by Zoee Perrine, Sangeeta Negi and Dick Sayre — which you can access here.  They write:

“At saturating light intensities, the rate of photon capture substantially (> 100 ×) exceeds the rate of linear photosynthetic electron transfer resulting in a large fraction of the captured light energy being dissipated as heat or fluorescence by non-photochemical quenching (NPQ) processes.”



Think of the problem as one of Alga A and Alga B. Both would benefit by cooperating to harvest less light and process it more efficiently. But there is the betrayal option — harvest more light at the expense of the other. Algae generally have chosen the betrayal option over the years.

In their latest research, Perrine, Negi and Sayre are exploring the impact of reducing chlorophyll  levels in their model algae (Chlamydomonas reinhardtii) — sure enough, they found that by reducing light harvesting capabilities they found “a two-fold increase in photosynthetic rate at high light intensities and a 30% increase in growth rate at saturating light intensities.”

Why do algae misbehave?

So — why exactly are algae committed to a strategy that results in a lower growth rate? The researchers hypothesize that “the large antennae size of wild-type algae and land plants offers a competitive advantage in mixed cultures due to the ability of photosynthetic organisms with large light harvesting antennae to shade competing species and to harvest light at low flux densities.” They might also find in later studies that lower growth rates in algal communities conserve nutrient loads in the water. We’ll see.

A Nash Equilibrium

What they are describing is a version of what DVD owners of A Beautiful Mind might describe as a Nash equilibrium — a state in a game where all players have made an optimal choice for themselves, given what they can surmise about the choices that will be made by others.

(Have you ever noticed that no one likes to take the first slice of cake, or the last — but the middle pieces seem to go awfully quickly? There, you are looking at states in the “game of cake eating” that have a transitory equilibrium).

For algae biofuels, we have a solution that tests our thinking about the powers of evolution. Sometimes, we surmise, it is not appropriate to engineer a superior version of an organism because if Nature had, over 300 million years, not selected for such an option, “there must be a reason.”

Communities vs individuals

True, there is a reason. But the reasoning of Nature is clouded within the problem of the Prisoner’s Dilemma in  biology. Here’s the problem. Communities may derive benefits, but individuals make choices. Not every organism makes the co-operative choice that benefits the community.

Fixing the Problem

In biology, we have access to new strategies through transgenic research — which affords us the option to consider strategies that benefit the community, even when the individual organisms do not have perfect information about the actions that will be taken by the other “prisoners”.

As can be seen in the research by Perrine, Negi, and Sayre — a more optimal light distribution strategy is available to algae but they don’t take it, because they find themselves in the Prisoner’s Dilemma, unable to communicate with each other and co-operate for maximum mutual benefit.

With a shorter cross-section in the light-harvesting antennae, and when living in monocultures, the algae community simply grows faster, with improved photosynthetic efficiency and productivity.

More productivity, more algae, more biomass for harvest, more general benefits for the community. And not bad, either, for the individuals. It prompts us, as actors within the system, to take steps to care for and enhance algae — at the expense of their competitors in the water.

Print Friendly, PDF & Email

Tags: , , ,

Category: Top Stories

Thank you for visting the Digest.