Can Microbes Compute?


Researchers from the Unconventional Computing Center (I did not make that up) in the UK have figured out, at least theoretically, how to use microbes as computers. Mind you, there won’t be a biological computer sitting on your desk any time soon, but the prospect of finding new computational methods that don’t use the conventional silicon chips is exciting. In fact, in a configuration called a microbial fuel cell (MFC), microbes generate the electricity needed to run the computer that they are part of. A clever arrangement of these MFC cells can become something called a cellular automata, allowing the resulting network of cells to perform computations. Cellular automata is a concept we need to unpack a little bit for all this to make a bit more sense and understand why it’s important.

Imagine a black square, representing a cell. Around this square, you could fit eight other square neighbours, arranged like the face of a Rubik’s cube. Now visualise that black square on a grid, like a scrabble piece on a scrabble board. You can then imagine writing a set of rules that dictate whether that square is “black” or “white” (or, equivalently, “on” or “off”, “alive” or “dead”), and those rules depend on whether the neighbors are themselves black or white. If those rules are well chosen, all you’ll have to do is assign an initial state (whether cells are black or white at the initial start of the experiment), “press play”, and the system will evolve by turning either black or white. The patterns will almost look as if it has “behavior”. This is essentially what a cellular automata is: a set of cells on a (possibly multi-dimensional!) grid obeying fixed rules regarding how to behave depending on their neighbor’s state. The most famous cellular automata is called Conway’s Game of Life (GoL). The wikipedia article of Conway’s GoL shows an animated illustration of Conway’s rules on a 2D grid. In preparing this article, I also discovered an easter egg on Google Search (start typing: Conway’s game of life on Google and see what happens!)

Conway’s Game of Life

Computers operate by opening and closing small electronic components called transistors, which are thus either on or off, which is interpreted by software as either 1 and 0 – a change of “state”. A computation is essentially a fancy sequence of 1’s and 0’s, so you can likely broadly appreciate how a cellular automata can be linked to computation.

Now, what about microbial fuel cells (MFC)? They are pretty incredible. A “traditional” fuel cell is a device that can capture electrons (the currency of electricity) that travel between a positively charged surface (a cathode) to a negatively charged one (an anode). It is thus a device that controls a chemical reaction with the purpose of harnessing those electrons. Some microbes generate electrons as a byproduct of them processing their food (which can be waste water, or dirt), so a Microbial Fuel Cell is a bioelectrical device that smartly uses biology to generate the electrons. All you have to supply is the food.

So to put everything together, these researchers have theoretically been able to create an arrangement of MFC’s (two, to be precise – a “duet”) that can replicate the rules of one of Conway’s cells. By placing these blocks of two MFC’s together in a grid, they have shown that, in principle, Conway’s GoL could be created. And thus the allure of biological computation! Of course, there is a long way to go before this type of computation becomes “practical”, and it may never fully replace silicon based computers. After all, electronic transistors change states (go from on to off) in nanoseconds, while it takes a few minutes for the MFC “duet” to change state. A span of minutes may seem impractical, but remember –  they are also energy independent, unlike transistors. More research will likely speed things up, and the faster they get, the more applications will open up. Energy independent computing enabled by biology. Now that’s sciworthy.

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