AFM Studies of Bacterial Biofilms

Dr. I.B. Beech, Dr. J.R. Smith, School of Chemistry, Physics and Radiography, University of Portsmouth, White Swan Road, Portsmouth P01 2DT, U.K.

The formation of biofilms on stainless steel surfaces increases the rate of steel corrosion. The ability of AFM to image biofilms in an aqueous environment and to perform in situ real-time experiments makes it an invaluable tool for studying both biofilm growth and the subsequent steel corrosion. At the University of Portsmouth, AFM is being utilized to study naturally occurring biofilms on stainless steel surfaces (1).
[Biofilm] [Biofilm] Click image for a closer look, click ICON for a high resolution (JPG) file 138k.

Figure 1, Contact mode AFM image of a marine sulfate reducing bacteria biofilm on 316 stainless steel.

Figure 1 shows a biofilm formed by marine-sulfate reducing bacterium on the surface of 316 stainless steel. The image was aquired using contact mode AFM with a TopoMetrix Discoverer™. The bacterium was grown on 316 stainless steel surfaces which had been polished to a 1µm surface finish by exposure to acid steamers for 30 days. Bacterial cells are observed either fully or partially embedded in an extracellular polymer matrix in accordance with complementary environmental scanning electron microscope (ESEM) experiments. Following removal of the biofilms, quantitative AFM analysis revealed the presence of numerous micropits which had not been visible on the virgin steel surface. The deterioration of the steel beneath the biofilm was further evidenced by an increase in the average arithmetic area surface roughness (Ra) from 9.2nm to 16.7nm after removal of the biofilm.

[Biofilm] [Biofilm] Click image for a closer look, click ICON for a high resolution (JPG) file 116k.

Figure 2, Zoomed scan on a single sulfate reducing bacterium.

AFM analysis of an individual bacterium (Figure 2) highlights the presence of capsular extracellular polymeric substances with an average width of 0.27µm. The topography of this sessile sulfate reducing bacterium (SRB) cell reveals a mosaic-like structure composed of small units. An individual flagellum is observed protruding from the cell.

In addition to the high resolution imaging of these molecules, TopoMetrix Layered Imaging™ software can be used to acquire a matrix of images as a function of probe force, enabling compliance and adhesion data to be extracted from all points on the cell. The advantage of using AFM to characterize these systems lies in its ability to provide detailed structural information at nanometer resolution combined with the quantitative monitoring of in-situ corrosion reactions. This work forms part of a project aimed at using AFM to understand the mechanisms involved in steel corrosion in the presence of biofilms and to subsequently develop biocides to inhibit biofilm growth.

REFERENCES

(1) - I.B. Beech, J.R. Smith, B.B. Johnson, C.W.S. Cheung, Biofouling, in press

Re-printed from the Summer 1996 Applications Newsletter Volume 96-1 : For a hard copy, contact Support -
Jan McNerney janmc@topometrix.com

Other articles from the TopoMetrix Applications Newsletter - Summer 1996
[Geochem] (010) Barium Sulfate Growth "SPM Applications in Geochemistry and Minerals Technology"
[folant]FOLANT Method Offers Unique Capabilities "Nanostructuring Using Combined Laser / STM"
[Magneto-Optic NSOM] Magneto-Optic NSOM "Magneto-optic Investigations With Aurora™ NSOM"
[NSOM res]Near-field Optical Microscopy "A Breakthrough in Resolution"

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