As we walk through our daily environments, we’re surrounded by exotic creatures that are too small to see with the naked eye. We usually imagine these microscopic organisms, or microbes, as asocial cells that float around by themselves. But in reality, microbes gather by the millions to form vast communities known as biofilms. Natural biofilms are like miniature jungles filled with many kinds of microbes from across the web of life. Bacteria and archaea mingle with other microbes like algae, fungi, and protozoa, forming dense, organized structures that grow on almost any surface.
When you pad across a river bottom, touch the rind of an aged cheese, tend your garden soil, or brush your teeth, you’re coming into contact with these invisible ecosystems. To see how biofilms come about, let’s watch one as it develops on a submerged river rock. This type of biofilm might begin with a few bacteria swimming through their liquid environment. The cells use rotating flagella to propel towards the surface of the rock, which they attach to with the help of sticky appendages. Then, they start producing an extracellular matrix that holds them together as they divide and reproduce.
Before long, microcolonies arise, clusters of cells sheathed in this slimy, glue-like material. Microcolonies grow to become towers, while water channels flow around them, functioning like a basic circulatory system. But why do microbes build such complex communities when they could live alone? For one thing, microbes living in a biofilm are rooted in a relatively stable microenvironment where they may have access to a nutrient source. There’s also safety in numbers. Out in the deep, dark wilderness of the microbial world, isolated microbes face serious risks. Predators want to eat them, immune systems seek to destroy them, and there are physical dangers, too, like running out of water and drying up.
However, in a biofilm, the extracellular matrix shields microbes from external threats. Biofilms also enable interactions between individual cells. When microbes are packed against each other in close proximity, they can communicate, exchange genetic information, and engage in cooperative and competitive social behaviors. Take the soil in your garden, home to thousands of bacterial species. As one species colonizes a plant root, its individual cells might differentiate into various subpopulations, each carrying out a specific task. Matrix producers pump out the extracellular goo, swimmers assemble flagella and are free to move about or migrate, and spore-formers produce dormant, tough endospores that survive starvation, temperature extremes, and harmful radiation.
This phenomenon is called division of labor. Ultimately, it gives rise to a sophisticated system of cooperation that’s somewhat like a multicellular organism in itself. But because biofilms often contain many different microbes that aren’t closely related to each other, interactions can also be competitive. Bacteria launch vicious attacks on their competitors by secreting chemicals into the environment, or by deploying molecular spears to inject nearby cells with toxins that literally blow them up.
In the end, competition is all about resources. If one species eliminates another, it keeps more space and food for itself. Although this dramatic life cycle occurs beyond the limits of our vision, microbial communities provide humans and other species with tangible, and sometimes even delicious, benefits. Microbes make up a major fraction of the biomass on Earth and play a critical role within the global ecosystem that supports all larger organisms, including us.
They produce much of the oxygen we breath, and are recruited to clean up environmental pollution, like oil spills, or to treat our waste water. Not to mention, biofilms are normal and flavor enhancing parts of many of the foods we enjoy, including cheese, salami, and kombucha. So the next time you brush your teeth, bite into that cheese rind, sift through garden soil, or skip a river stone, look as close as you can. Imagine the microbial jungles all around you waiting to be discovered and explored.