Bacteria and the power of teamwork
Tess Shellard
The winners of the inaugural Wellcome Trust Science Writing Prize in association with the Guardian and the Observer were announced this week. We’ll be publishing each of the 30 shortlisted entries over the coming months, starting with Tess Shellard, winner of the Non-professional category for her essay on how bacteria communicate.
Imagine for a moment that we all have one firework and our sole purpose is simply to light it. With just one trick to last a lifetime it becomes a question of how best to use it, of timing. Setting it off randomly would achieve very little, few would even see it. But if you took a lesson from bacteria you would gather together to light them all at once, and illuminate the whole sky.
Bacteria play a crucial role in life on this planet. We are utterly reliant on them for our survival, covered in them inside and out, but nonetheless taught to only think of them as the enemy. They digest our food, synthesise our vitamins, help to make our wine and cheese – some of them even protect us from the worst of their family, the pathogens.
Previously the profound influence of bacteria was attributed to their sheer numbers, but there is a much greater sophistication to their success and it all stems from something we would never guess they could do. A single-celled dividing machine with very little genetic material, they have no ears to hear, no sense of touch, in fact none of our means of interpreting the outside world, and yet, a bacterium can tell if it is alone.
By secreting a chemical that can only be read by members of the same species, bacteria use the chemical’s concentration to tell how many siblings are nearby. This quorum sensing is then used for timing their gene expression. They don’t just act; they wait until they are enough of them for the action to be effective, they move as one team. It may not even be helpful to think of bacteria as unicellular anymore given this level of co-ordination.
Moreover, not only can a bacterium tell if kin are near, they can tell if they are among other types of bacteria. In addition to specific intra-species communication they use a chemical lingua franca shared among all bacteria. With this information, they can build alliances which help them all to thrive. This is nothing short of military strategy – albeit strategy without cognisance.
Professor Bonnie Bassler of Princeton’s Molecular Biology department led the research on quorum sensing. Her work on the exquisite symbiosis between Hawaiian bobtail squid and the bacteria Vibrio Fischeri showcases an expert use of quorum sensing in the squids’ mimicry of moonlight. By day the squid bury themselves in the sand, only coming out at night to hunt in the shallows, but they cast a shadow in the moonlit waters which leaves them vulnerable to predators.
The squid have sacs on their mantle in which the bacteria breed. When sufficient in number the bacteria collectively switch on their bioluminescence. This gently illuminates the seabed while the squid hunts, counteracting its moonlight shadow and silhouette. To get it just right, sensors on the squid’s back gauge the strength of moonlight, with filters adjusting the light emitted from the sacs accordingly.
In return for all this handy counter-illumination the bacteria are kept well fed, but the majority must be flushed out of the sacs in the morning. When their numbers suddenly drop below the quorum threshold, the bacteria simultaneously turn off their light. The remaining population do what they do best and multiply throughout the day, reaching sufficient numbers by nightfall to start glowing all over again. E voilà! All of the squid’s illumination-needs skilfully met for the bargain price of the odd sugar and amino acid supper.
Obviously not all bacteria are quite that endearing – chancing upon the wrong kind can definitely kill the mood, if not the entire host. Our response thus far has involved decimating the lethal ones with antibiotics but this has only served to rapidly select for resistance. Knowledge of quorum sensing, however, offers a fresh approach.
By interfering with the communication between deadly bacteria we can ensure they live out their days without ever fully expressing their pathogenicity, all the while wondering why no-one showed up to the party. As each species has its own language we can befuddle one species without disturbing the rest. Or if needed, use their lingua franca to befuddle the whole lot of them, in the way of broad-spectrum antibiotics. Conversely, for helpful bacteria we could artificially increase the volume of their conversation and so hasten gene expression. An entirely new frontier is beckoning.
We like to think the bigger the brain the better the story when it comes to life on earth but this is so often wrong. Bacteria are diminutive but they communicate in more than one language, they strategise, they co-ordinate their efforts, they have thrived in places you wouldn’t go for a dare. It seems clear the bacteria still have a lesson or two for us big-headed folk.
Tess Shellard
Find out more about the Wellcome Trust science writing prize and read our ‘How I write about science‘ series of tips for aspiring science writers.
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