Not Home Alone: Bacterial biofilms
Imagine for a moment that you are alone. I mean, really alone. There is nobody around you within sight or earshot, and when you call out nobody answers.
You start to go about your day, and at first it seems pretty easy. There is nobody in your way as you skip unashamedly down the uncrowded street! All the cake in the fridge is yours, no need to share! It’s a one-woman, or one-man, show! Like Kevin in Home Alone, you are finally free of all social norms and expectations. You’ve found paradise!
But then some things get harder.
Your internet stops working, and there is nobody on the other end of the telephone help line to re-connect it. With everybody else having vanished off the face of the earth, there are no new Netflix shows or YouTube videos to watch. Eventually you’ve emptied all nearby supermarkets of food, and there is nobody else left to produce it. Your heart starts to ache, along with your belly. Like Kevin, after a day or two, you feel lonely.
In my opinion, one of the greatest powers that humanity has is our ability to work together. We organise into groups, building multifaceted towns or cities that make our individual lives easier and richer, and allow us to specialise. If not for the hard-working farmers and trash collectors and supermarket cashiers, there is no way that I’d have the time to work in a laboratory or to write this blog. If you aim to be entirely self-sufficient, it can come at a heavy cost: the cost of spending all of your time on purely supporting your own basic needs.
Humans aren’t the only ones who’ve collectively come to this conclusion. For many years, it was believed that bacteria, unlike animals, lived lonely, unicellular lives, in the last decades scientists have come to understand that bacteria work together, too. In fact, the majority of bacteria are city-dwellers.
The scientific term for a bacterial city is a “biofilm”. Just like our own modern cities, biofilms are complex, multicultural entities – many different types of bacteria will join together in a biofilm for their collective good.
In all likelihood, you’ve probably seen a biofilm before – the slimy layer on the inside of your water bottle that develops when you don’t wash it out regularly enough, or on the surface of exposed metal piping that directs ditch water, or the plaque on your teeth. But the slimy look of a biofilm viewed with the naked eye doesn’t do due justice to the beautiful, bustling environment which it truly is.
Biofilms start to form when a few bacteria first attach to a surface. Just as for us humans, bacteria can gain some benefits by staying in one place rather than swimming around endlessly. For instance, stability in location usually also means some stability in environmental conditions, like temperature and acidity, which in turn gives a bacterium an easier go at life. To take an analogous situation for humans, I think most would have to admit that the drastic, temperature-changing Chinook winds in Calgary are a challenge to live with. Some stability in temperature and other environmental factors makes life easier, for humans and bacteria alike.
Once you've found a nice spot to begin forming a settlement, you can imagine that some communication is needed to convince others to move there, too. As a human forming a new settlement, you’ll probably begin to tell other people about it, and communicate in some way about your dreams for how the nascent city will develop. The same is true for bacteria.
Like human cells, bacteria can send out different genetic material, proteins, and lipids that serve as molecular mail to communicate with other cells around them. These molecular messages help the bacteria in biofilms self-organise into productive neighbourhoods. Different species of bacteria will arrange themselves into so-called ‘microenviroments’ that are built to suit their specific needs. For instance, some bacteria will prefer a slightly higher oxygen level than others. Those bacteria will congregate together, near the exposed surface of the biofilm – and in doing so, they will create the perfect low-oxygen environment at the biofilm's base layer, where other bacteria who aren’t quite so keen on oxygen can thrive. This system of bacterial communication by sending out materials to the surroundings, which scientists call “quorum sensing”, allows different types of bacteria to live together in harmony, and in a way which benefits all – a wonderfully harmonious note to end this first Microbial Mondays of 2022 on.
Until next time,
Don’t forget the importance of communication!