CBE Interdisciplinary Glossary

Table of Contents

I just got back from a lab grown culture, and, boy, are they homogeneous...

Cartoon by J. Pennington

Biofilm growth on an impeller (rotation speed 500 r.p.m.). When you consider that the impeller in the photo above is actually about 10 feet high, you can start to appreciate how BIG a problem biofilm can be for industry.
(Photo Credit: Atkinson, B. and Fowler, H.W., in (Photo Credit: Atkinson, B. and Fowler, H.W., in Biochemical Engineering Vol. 3, T.K. Ghose, A. Fiechter, and N. Blakerough (Eds). Springer-Verlag, Berlin (1974); figure added for scale.)

Introduction

Let's start with biofilm. What is it, exactly, and why are we studying it?

Biofilm is composed of millions of microorganisms (bacteria, fungi, algae, and protozoa) that accumulate on surfaces in aqueous environments.

These film-forming microbes excrete a glue-like substance that anchors them to materials such as metals, plastics, tissue, and soil particles. Once anchored to a surface, biofilm microorganisms carry out a variety of detrimental or beneficial reactions, depending on the surrounding conditions.The Center for Biofilm Engineering concerns itself with problems and potentials of biofilm formation.

Some of the problems associated with biofilm formation include biofouling, fouling or contamination linked to microbial activity; microbially influenced corrosion (MIC), especially of industrial pipes; oil field souring, the reduction of sulfates by microbes in soil; and infections caused by biofilm growing on host tissues or medical implants. Conservative estimates of the costs incurred by biofilm-related problems reach into the billions of dollars annually.

Not all biofilm activity has negative results. Bacteria within biofilms can break down contaminants in soil and water. Scientists and engineers work together to optimize the bioremediation of soils and water contaminated with toxic substances.
 

Center research is geared toward scale-up from laboratory studies to in-the-field solutions.

At the microscale, biofilms are remarkably similar, regardless of where they are found. Information gathered at this level can be applied to a variety of biofilm problems. Mesoscale, as the term is used at the CBE, can refer either to issues concerning the local environment of the biofilm or to the development of intermediary (bench test) experiments. The term macroscale applies to the real-world problem site, regardless of its actual size. Sometimes the macroscale involves an oil field; sometimes it concerns a contaminated catheter.

Successful research depends on continuous communication between these scales of observation - from micro to macro and back. Feedback from the macroscale is provided by the CBE's Industrial Associates (sponsors).

Biofilm Structure - at the Microscale

Even a few years ago, our concept of biofilm was simply that it was a continuous layer of slime containing microorganisms and other embedded material (Fig. 1).

Figure 1.

Recent improvements in research techniques have permitted us to get a better idea of biofilm structure, and we have seen that it is not as uniform as we once thought (Fig. 2). Understanding the variations in biofilm structure will help us understand issues of transport and chemistry in the biofilm.

Figure 2.

All seriousness aside:

Cluster: Refers to a group of some things (e.g., peanuts).

Void: Refers to the "Great Nothingness", which can actually be reflected in the eyes of many homo sapiens.

Pore: This can be thought of as a "door" or "portal" leading somewhere ... usually into the Void!

Channel: This is a 4-dimensional (time travelers know this!) conduit through which images can pass and end up in 3 dimensions.

Basic Biofilm Terminology

Some of the terms used at the CBE to describe biofilm structure are:

CLUSTER  A discrete aggregate of bacterial cells in an exopolymeric matrix. We have calculated that there are about 10 thousand million cells in 1 ml of cluster material. The clusters we have seen so far tend to be between 20 and 300 mm across and 20 and 200 mm high.

VOID  Absence of clusters; i.e., the separating spaces between the clusters. The voids are open to the bulk fluid, which can flow through them. There are very few, if any, cells in the voids (apart from those attached to the substratum). There may be some low density exopolymeric strands within the voids. Essentially we see them as empty spaces filled with bulk fluid.

CHANNEL is another expression for void. It implies that the voids are forming conduits which allow liquid to flow through the biofilm; i.e., the voids are facilitating transport processes.

PORE  This is a void that goes from the bulk fluid to inside the biofilm in a more or less vertical orientation. This is a term that we used when first applying terminology to the biofilm structure, and has turned out not to be very useful. The term was coined to imply the notion that the voids were allowing liquid, chemical, etc. exchange between the biofilm and the bulk fluid.

MATRIX The network of polymeric material that anchors cells to a substratum. A matrix also extends between cells within a single microcolony and between cells in adjacent microcolonies.

HETEROGENEITY

The term heterogeneity refers to the non-uniformity of physical, chemical and biological characteristics of biofilms at surfaces.

For years, microbiologists have recognized biological heterogeneity on surfaces from microscopic detection of microcolonies of morphologically distinct microorganisms in biofilms. Surface scientists have also recognized the variations in the chemistry and topography of both natural and man-made substrata that microorganisms colonize. Now, with the development of microsensors and 3-D microscopic imaging, we are beginning to recognize the existence of chemical gradients established as a result of the patchiness of microbial cell distribution and the different metabolic activities of a physiologically diverse microbial population. The combined effects of substratum variations, cell distribution and diversity, and chemical gradients in a biofilm result in medical implant-related infections, altered biocide efficacy and material deterioration and corrosion.
 

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