Quorum Sensing

Imagine yourself as a single-cell bacterium. You are happily living in your colony until one day, for reasons far beyond anyone’s control, your community’s reserve of nutrients is depleted. Your search for sustenance turns futile and now, it seems, the end is neigh.

Now, as a bacterium, you have two options for responding to this dire situation: sporulation or competence.

Sporulation essentially means choosing death. But before you perish you replicate your genome, wrap it in a membrane, and leave it behind as a genetic copy of yourself that can germinate again later when conditions are more favourable. By entering this dormant condition you embrace your demise, but your genetic code is left behind. As a spore, your DNA is almost indestructible: it is even able to withstand the solar electromagnetic radiation of outer space. (Horneck 1994)

Competence is your other option. All around you, millions of fellow bacteria are sporulating, and when they perish they leave behind their original genetic nucleotides, after encasing their new copied DNA in a spore. You are now surrounded by a supply of nutrients and bits of genetic code that could be very valuable to you. So maybe you should hold off on sporulating? But what if everyone else was to stop sporulating too? Then you would be in real trouble because it means you may have missed your opportunity to sporulate when you had the chance.

So how do you decide what to do? Well, in the absence of actually having a brain, you will not spend too much time fretting over the options. Rather, you are genetically wired to make this decision in concert with the rest of the colony. On a regular interval, you and every other bacterium emit a chemical signal expressing your current level of stress. Through this massive exchange of information, everyone knows the collective stress level of the community. This information is routinely processed by your genetic circuitry, as if by an interval timer. If stress levels are high enough, a random switch is thrown, determining whether or not you will sporulate. In other words, the signals you receive from your community set the threshold for your own ‘decision’. Your decision, in turn, affects the threshold for the decisions of other cells. In this way, you are part of a massive self-regulating process. You are part of assuring adequate sporulation for future colonization, as well as calculating precise resource requirements of the present. (Schultz, et al, 2013)

Bacteria are living proof that the most expansive, adaptive, resilient, and successful forms of life are those that make collective ‘decisions’ to determine the needs of the present in light of the future. As a rudimentary form of life, and the most abundant kind of life on Earth, bacteria represent something fundamental about the nature of life itself.

Bacteria do not even have a cellular nucleus, but they are extremely self-organized nonetheless. Their ‘decision-making process’ is a huge enterprise of quorum sensing. There is no such thing as an isolated choice when it comes to making decisions about the future of your colony. Every choice is influenced by every other choice — and every choice influences every other choice in turn.

There is little reason to think that the choices we make about our future, today, are any less consequential in the lives of those around us.

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