The objectives of this section are to provide you with
an understanding of some of the key characteristics of biofilms;
a recognition of how microorganisms that are part of a biofilm are different from those same microorganisms in isolation.
Upon completion of this section, you will be able
to summarize some of the key characteristics of biofilms;
to discuss some of the ways in which microorganisms which are part of a biofilm differ from the same microorganisms that exist in isolation;
to describe why microorganisms that exist in a biofilm are harder to destroy than the same microorganisms in isolation;
to discuss how microorganisms in a biofilm can communicate with each other.
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 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).
Permission pending, Z. Lewandowski and W. Dickinson, Center for Biofilm Engineering, Montana State University, Bozeman
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 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.
P. Dirckx, Center for Biofilm Engineering, Montana State University, Bozeman