In a sense, biofilms are like cities. Similar to city dwellers, microorganisms pass up solitary life to live communally [source: Watnick and Kolter]. We'll use Watnick and Kolter's analogy describing biofilms as "cities of microbes" to understand how cells in a biofilm interact.
As we discussed earlier, microbes colonize surfaces to build the foundation of a biofilm. Before settling down, some cells move around using flagella or other mobile structures until they find a suitable place to stay -- much like how new residents of a city visit different neighborhoods before choosing a home.
After moving in, new residents may add a room to their new home to create more space for people in a crowded house. In comparison, cells in a biofilm will produce those extracellular polysaccharide substances (EPSs) to include new cells from the outside and other cells created within the community. At a basic level, both cities and biofilms offer their residents protection from outside forces. For bacteria, these forces can be antibiotics or even the human immune system [source: Lemon et al.]. Scientists think a biofilm's overall thickness and density provide some protection [source: Montana State University CBE].
Also, communicating with your neighbors can be easier if you live closer to them. The same principle applies to cells in a biofilm during quorum sensing, when cells are near enough to signal effectively. Researchers hypothesize that this method may be used to establish boundaries between different biofilm colonies as well [source: Watnick and Kolter]. Living in biofilms makes it easier for cells to conjugate, or transfer genetic material, too.
Another important concept to remember is that biofilm structures are flexible. This is why they can be problematic. Most scientists use the term viscoelastic to describe biofilms, meaning they can be stretched like putty when the flow of a liquid pulls or pushes on the colony [source: Montana State University CBE]. These shear forces, or rates of liquid flow, can shape a biofilm colony and cause clumps to disconnect or tumble away.
What if our newcomers to the city grow tired of living in a crowded area? They may move somewhere else. Cells in a biofilm can do the same by detaching from the colony, regaining their mobility and continuing life as floating microorganisms. Detaching may be a harder task for cells embedded beneath other layers of cells and EPSs. After detaching, a microbe may even start its own biofilm or live in another established cell community. We don't know what causes detachment, but scientists say that species type, environmental pressures and competition within the biofilm all play strong roles. Like humans and other animals, microorganisms often move elsewhere to survive when the going gets tough.
Keep reading to learn how these microbe cities can be harmful to people.