What are Key Characteristics of Biofilms?

About This Section

In this section we introduce you to some of the key characteristics of biofilms. When we as scientists and engineers begin to learn about a new life system in order to exploit it for good or to destroy it if it is harmful, we need to understand as much as possible about it. What are its characteristics, and how will this knowledge help us accomplish what we need to do? The more we know about how a system functions, the more we know about how to deal with it. Quite a few things are now known about biofilms, but there is a lot left to uncover. We discuss a few of the things we have learned about biofilms here that help give us insight into why traditional forms of treatment do not seem to work well on biofilms and how we might develop more effective treatments. This overview will prepare you for later modules in which some of these things are explored in depth.

Biofilms are Complex, Dynamic Structures

Biofilms are remarkably heterogeneous. Many measurements and observations have been made of various biofilms; they all point to the diversity of individual biofilm colonies. As we have mentioned before, in typical, naturally occurring biofilms (as opposed to some that are grown in a laboratory for experimental reasons) there are nearly always a large number of different kinds of microorganisms living together. In addition, different biofilms seem to exhibit different internal structures, different chemical properties, different electrical properties, and, indeed, different properties of just about any other measurement or observation that can be made. Each of these properties seems to contribute to the characteristics of the biofilm as a whole that make it different (e.g., hard to kill) compared to dealing with each of the microorganisms in isolation (not in a biofilm, but in a planktonic environment).

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Permission pending, Z. Lewandowski and W. Dickinson, Center for Biofilm Engineering, Montana State University, Bozeman

Figure 1. Pitting corrosion on 316S stainless steel.

An example of microbially influenced corrosion. (Image, courtesy of Z. Lewandowski and W. Dickinson, MSU-CBE)

So here is a big question. If there is such a wide diversity of properties in different biofilms, how can we expect to find characteristics that apply to all biofilms? We are glad you ask. What has been discovered is that in spite of their wide diversity, biofilms do seem to have some common attributes, such as their ability to grow on virtually any surface, how they attach to a surface, their mode of growth, their ability to spread, how they are nourished, how they maintain themselves as a colony, and so forth.

For example, the image at the right shows pitting and corrosion of a stainless steel surface. This was caused by a biofilm, whose presence influenced how and how fast minerals were deposited on the surface. This, in turn, modified the electrochemical properties of the stainless steel, which caused the pitting corrosion of this seemingly impervious metal.

Can we extend what we learn about this kind of biofilm to other sorts of biofilms, such as plaque on teeth? Apparently so, as discussed in the rest of this section.

Here are some of the more evident characteristics common to all observed biofilms:

• biofilms are dynamic and responsive to their environment; that is, they can adapt to changes in their environment.
• a phenomenon known as detachment seems to be common among all biofilms. Bacterial cells can detach from their biofilm colony individually or in clumps.
• when individual microorganisms detach from a biofilm, these isolated microorganisms are relatively easy to kill with chemicals designed for this purpose.
• when microorganisms detach from their biofilm colony in clumps, the clumps are pieces of the biofilm that are at the moment not attached to a surface; in this case they maintain the protective properties of the original biofilm and are thus much more difficult to kill.
• in the right conditions, biofilms can migrate across surfaces over a period of time in a variety of ways, as illustrated below.

Biofilms appear to show aspects of both solids and liquids—much like slug slime—and fall into a category called "viscoelastic." However, as biofilms collect sediment, or become scaled with rust or calcium deposits, they become less fluid and more like a brittle solid.

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P. Dirckx, Center for Biofilm Engineering, Montana State University, Bozeman

Figure 2. Biofilm Migration.