Bacteria As Fuel Cells?

KantIsDead writes "MIT's Tech Review is running an interview with Boston University Bioengineer Tim Gardner about the possibility of using bacteria to produce electricity. If fuel cells running off sugar are nearly here, alcohol-powered robots cannot be far." From the article: "While typical fuel cells use hydrogen as fuel, separating out electrons to create electricity, bacteria can use a wide variety of nutrients as fuel. Some species, such as Shewanella oneidensis and Rhodoferax ferrireducens, turn these nutrients directly into electrons. Indeed, scientists have already created experimental microbial fuel cells that can run off glucose and sewage. Although these microscopic organisms are remarkably efficient at producing energy, they don't make enough of it for practical applications."

Comments

Make bacteria dependent i.e lac operon, etc

[spineboy]

Make the bacteria dependent on an added compound that is associated with the genes you want to keep. Use the lac operon as an example - add lactate and the gene switches on, but in our bacteria, it turns on a gene cascade that produces the enzymes that give us EtOH/electricity as well as another product that the bacteria needs to survive. If the bacteria kicks out the desired gene that we want, it also kicks out the compound that regulates its cell cycle, and it dies.

It would be unlikely for the bacteria to spontaneously mutate out 2 genes at once, thereby subverting our design. Obviously bacteria, number in the billions, so it will be necessary to restock our fuel cell occasionally. Of course you could be clever and tie in a third gene that gives immunity to a toxic substance, so that non-desired mutated bacteria are killed off automatically.

Bacteria Can't Scale?

[Phat_Tony]

Although these microscopic organisms are remarkably efficient at producing energy, they don't make enough of it

There's something wrong with this sentence. It sounds like they're saying that the bacteria perform an efficient conversion of the sugar energy into electrical energy, but that the problem is that bacteria can't be scaled effectively to produce significant amounts of power.

There's a problem with the idea that bacteria don't scale. Bacteria are well known for their exponential growth curves. Give me a sufficently large petri dish with medium and a starter batch of bacteria, and I'll solve your scaling dilemma.

If they are truly efficient, then there's no problem with bacteria not making enough power, as making more bacteria is trivial. However, I don't think it's likely they really are efficient. It seems highly unlikely bacteria would waste much energy on producing unused electricity, one might expect them, like most living things, to use most of their available energy growing, respirating, reproducing, and anything else that generally falls under the category of "surviving." Sure enough, later in the article comes:

Gardner's team aims to harness the genetic control system to engineer bacteria that can produce energy more efficiently.

Which makes me think that the problem with the current bacteria is efficiency, not scalability, as the first sentence implies. Perhaps by "efficient" he means that they don't produce a lot of waste heat or something, but for generating electricity, the definition of efficiency should be what percent of the energy they take in they put back out as electricity.