Bio-electric slide

Microbial ecology meets electrochemistry: electricity-driven and driving communities.
http://www.ncbi.nlm.nih.gov/pubmed/18043609

I'm going to explore a different tactic for this week, which is provide a review of... a review! This field is fascinating but still nascent and therefore highly technical. Therefore I'll try to boil down an overview of this topic so something even shorter, simpler and, with luck, sweeter. You may ask about its relation to neuroscience but if you get to the end you'll see my plug for why neurons might be useful to consider.

The future of energy
As oil prices rise and supplies of fossil fuels dwindle, it has become clear the the future of energy lies in currently underutilized sources. In terms of generating electricity, probably the most important form of energy our world needs, we have heard a lot about solar and wind power lately. Hydro-electric power is seeing heavy use in developing countries such as China, but does have some significant ecological side-effects, especially if its implementation is not well thought-out. You may be aware of even newer and more unconventional technologies for energy generation, such as bio-diesel, ethanol, and methane extraction from farm waste (all of these methods rely on combustion).

The bottom line is, we are going to need to harness ALL available sources of energy that we can conceive of in order to meet our future energy needs, both static (the electric grid) and portable (vehicles). One rapidly developing area of research involves harnessing bacteria to generate power. Some early designs include the use of methane-producing bacteria to consume sewage or other waste water and release methane or other combustible gases.

Bio-electricity as an energy source
A newer direction for biological research in the field of energy generation is harnessing bio-electricity. All living cells are constantly generating a little bit of electricity in the form of a voltage across the membrane that separates the inside of the cell from the outside world. This lipid membrane forms what we call a 'capacitor'; that is, it separates charges and stores energy. The capacitor is charged by small currents that cross the cell's membrane, carried by ions (such as sodium and potassium) in water. This is as opposed to the system of electricity we typically think of, which involves (roughly) the flow of electrons through an organized metal lattice - a copper wire, for instance. It would be great if we could access that energy - however, this would require us to hook up wires outside the cell (not too much of a problem) and also inside the cell (well, that is a problem). How can you get access to the inside of a cell without killing it? The answer is, you can, but it's difficult and time-consuming. Some people are actually thinking about it, but we can come back to that later.

However, there are also bacteria, discovered in the early 20th century, that can actually generate electric currents outside of themselves, without any involvement (or at least minimal involvement) of the cell's interior. Now we're talking. How does this work? Interestingly, these bacteria facilitate the transfer of electrons from organic matter (ie. sewage or other organic waste) to metals like iron - or indeed, to an electrical anode. In a battery, the anode is the metal contact that receives electrons. Therefore, these bacteria, when mixed with organic matter, and grown on an anode (the bacteria tend to grow as a thin film, or biofilm) within a battery will actual power that battery. So far researchers have achieved near 1 Volt and several milliamps of power from a small bacteria-fueled battery. In larger installations, up to 1 kWh of electricity can be gleaned from 1 kg of waste (1 kWh, or kilowatt-hour, is the amount of power that ten 100-watt light bulbs use in an hour).

Although these amounts of power are small, and currently somewhat inefficient, this design is in its infancy. A further amazing feature of bio-electric batteries is that if the bacteria inside are grown over time (unclear from the article but I would guess days to weeks), the circuit becomes MORE efficient as the bacterial community develops and interacts. Perhaps the bacteria are trying to help us out with this energy problem?

Some researchers have, at a purely theoretical level, already begun to model the possibility of harnessing the type of electricity I mentioned beforehand. In other words, they are designing models that involve harnessing the voltage and currents that cells use across their membranes. Brain cells are some of the most electrically active, diverse, and efficient cells in the body. If we could find a way to harness the electrical energy of neurons or an artificial system based upon their physiology, we would have a real winner. Another cell type that merits study is the electric organ of the electric eel which can generate several hundred volts within close proximity to the snimal. I'm not suggesting that we have huge tanks full of eels to power our houses (although apparently they do in Japan) - but you certainly keep an eye out for these interesting ideas when it comes to the future of energy, and our world.